Source file src/reflect/value.go

Documentation: reflect

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package reflect
     6  
     7  import (
     8  	"math"
     9  	"runtime"
    10  	"unsafe"
    11  )
    12  
    13  const ptrSize = 4 << (^uintptr(0) >> 63) // unsafe.Sizeof(uintptr(0)) but an ideal const
    14  
    15  // Value is the reflection interface to a Go value.
    16  //
    17  // Not all methods apply to all kinds of values. Restrictions,
    18  // if any, are noted in the documentation for each method.
    19  // Use the Kind method to find out the kind of value before
    20  // calling kind-specific methods. Calling a method
    21  // inappropriate to the kind of type causes a run time panic.
    22  //
    23  // The zero Value represents no value.
    24  // Its IsValid method returns false, its Kind method returns Invalid,
    25  // its String method returns "<invalid Value>", and all other methods panic.
    26  // Most functions and methods never return an invalid value.
    27  // If one does, its documentation states the conditions explicitly.
    28  //
    29  // A Value can be used concurrently by multiple goroutines provided that
    30  // the underlying Go value can be used concurrently for the equivalent
    31  // direct operations.
    32  //
    33  // To compare two Values, compare the results of the Interface method.
    34  // Using == on two Values does not compare the underlying values
    35  // they represent.
    36  type Value struct {
    37  	// typ holds the type of the value represented by a Value.
    38  	typ *rtype
    39  
    40  	// Pointer-valued data or, if flagIndir is set, pointer to data.
    41  	// Valid when either flagIndir is set or typ.pointers() is true.
    42  	ptr unsafe.Pointer
    43  
    44  	// flag holds metadata about the value.
    45  	// The lowest bits are flag bits:
    46  	//	- flagStickyRO: obtained via unexported not embedded field, so read-only
    47  	//	- flagEmbedRO: obtained via unexported embedded field, so read-only
    48  	//	- flagIndir: val holds a pointer to the data
    49  	//	- flagAddr: v.CanAddr is true (implies flagIndir)
    50  	//	- flagMethod: v is a method value.
    51  	// The next five bits give the Kind of the value.
    52  	// This repeats typ.Kind() except for method values.
    53  	// The remaining 23+ bits give a method number for method values.
    54  	// If flag.kind() != Func, code can assume that flagMethod is unset.
    55  	// If ifaceIndir(typ), code can assume that flagIndir is set.
    56  	flag
    57  
    58  	// A method value represents a curried method invocation
    59  	// like r.Read for some receiver r. The typ+val+flag bits describe
    60  	// the receiver r, but the flag's Kind bits say Func (methods are
    61  	// functions), and the top bits of the flag give the method number
    62  	// in r's type's method table.
    63  }
    64  
    65  type flag uintptr
    66  
    67  const (
    68  	flagKindWidth        = 5 // there are 27 kinds
    69  	flagKindMask    flag = 1<<flagKindWidth - 1
    70  	flagStickyRO    flag = 1 << 5
    71  	flagEmbedRO     flag = 1 << 6
    72  	flagIndir       flag = 1 << 7
    73  	flagAddr        flag = 1 << 8
    74  	flagMethod      flag = 1 << 9
    75  	flagMethodShift      = 10
    76  	flagRO          flag = flagStickyRO | flagEmbedRO
    77  )
    78  
    79  func (f flag) kind() Kind {
    80  	return Kind(f & flagKindMask)
    81  }
    82  
    83  func (f flag) ro() flag {
    84  	if f&flagRO != 0 {
    85  		return flagStickyRO
    86  	}
    87  	return 0
    88  }
    89  
    90  // pointer returns the underlying pointer represented by v.
    91  // v.Kind() must be Ptr, Map, Chan, Func, or UnsafePointer
    92  func (v Value) pointer() unsafe.Pointer {
    93  	if v.typ.size != ptrSize || !v.typ.pointers() {
    94  		panic("can't call pointer on a non-pointer Value")
    95  	}
    96  	if v.flag&flagIndir != 0 {
    97  		return *(*unsafe.Pointer)(v.ptr)
    98  	}
    99  	return v.ptr
   100  }
   101  
   102  // packEface converts v to the empty interface.
   103  func packEface(v Value) interface{} {
   104  	t := v.typ
   105  	var i interface{}
   106  	e := (*emptyInterface)(unsafe.Pointer(&i))
   107  	// First, fill in the data portion of the interface.
   108  	switch {
   109  	case ifaceIndir(t):
   110  		if v.flag&flagIndir == 0 {
   111  			panic("bad indir")
   112  		}
   113  		// Value is indirect, and so is the interface we're making.
   114  		ptr := v.ptr
   115  		if v.flag&flagAddr != 0 {
   116  			// TODO: pass safe boolean from valueInterface so
   117  			// we don't need to copy if safe==true?
   118  			c := unsafe_New(t)
   119  			typedmemmove(t, c, ptr)
   120  			ptr = c
   121  		}
   122  		e.word = ptr
   123  	case v.flag&flagIndir != 0:
   124  		// Value is indirect, but interface is direct. We need
   125  		// to load the data at v.ptr into the interface data word.
   126  		e.word = *(*unsafe.Pointer)(v.ptr)
   127  	default:
   128  		// Value is direct, and so is the interface.
   129  		e.word = v.ptr
   130  	}
   131  	// Now, fill in the type portion. We're very careful here not
   132  	// to have any operation between the e.word and e.typ assignments
   133  	// that would let the garbage collector observe the partially-built
   134  	// interface value.
   135  	e.typ = t
   136  	return i
   137  }
   138  
   139  // unpackEface converts the empty interface i to a Value.
   140  func unpackEface(i interface{}) Value {
   141  	e := (*emptyInterface)(unsafe.Pointer(&i))
   142  	// NOTE: don't read e.word until we know whether it is really a pointer or not.
   143  	t := e.typ
   144  	if t == nil {
   145  		return Value{}
   146  	}
   147  	f := flag(t.Kind())
   148  	if ifaceIndir(t) {
   149  		f |= flagIndir
   150  	}
   151  	return Value{t, e.word, f}
   152  }
   153  
   154  // A ValueError occurs when a Value method is invoked on
   155  // a Value that does not support it. Such cases are documented
   156  // in the description of each method.
   157  type ValueError struct {
   158  	Method string
   159  	Kind   Kind
   160  }
   161  
   162  func (e *ValueError) Error() string {
   163  	if e.Kind == 0 {
   164  		return "reflect: call of " + e.Method + " on zero Value"
   165  	}
   166  	return "reflect: call of " + e.Method + " on " + e.Kind.String() + " Value"
   167  }
   168  
   169  // methodName returns the name of the calling method,
   170  // assumed to be two stack frames above.
   171  func methodName() string {
   172  	pc, _, _, _ := runtime.Caller(2)
   173  	f := runtime.FuncForPC(pc)
   174  	if f == nil {
   175  		return "unknown method"
   176  	}
   177  	return f.Name()
   178  }
   179  
   180  // emptyInterface is the header for an interface{} value.
   181  type emptyInterface struct {
   182  	typ  *rtype
   183  	word unsafe.Pointer
   184  }
   185  
   186  // nonEmptyInterface is the header for an interface value with methods.
   187  type nonEmptyInterface struct {
   188  	// see ../runtime/iface.go:/Itab
   189  	itab *struct {
   190  		ityp *rtype // static interface type
   191  		typ  *rtype // dynamic concrete type
   192  		hash uint32 // copy of typ.hash
   193  		_    [4]byte
   194  		fun  [100000]unsafe.Pointer // method table
   195  	}
   196  	word unsafe.Pointer
   197  }
   198  
   199  // mustBe panics if f's kind is not expected.
   200  // Making this a method on flag instead of on Value
   201  // (and embedding flag in Value) means that we can write
   202  // the very clear v.mustBe(Bool) and have it compile into
   203  // v.flag.mustBe(Bool), which will only bother to copy the
   204  // single important word for the receiver.
   205  func (f flag) mustBe(expected Kind) {
   206  	if f.kind() != expected {
   207  		panic(&ValueError{methodName(), f.kind()})
   208  	}
   209  }
   210  
   211  // mustBeExported panics if f records that the value was obtained using
   212  // an unexported field.
   213  func (f flag) mustBeExported() {
   214  	if f == 0 {
   215  		panic(&ValueError{methodName(), 0})
   216  	}
   217  	if f&flagRO != 0 {
   218  		panic("reflect: " + methodName() + " using value obtained using unexported field")
   219  	}
   220  }
   221  
   222  // mustBeAssignable panics if f records that the value is not assignable,
   223  // which is to say that either it was obtained using an unexported field
   224  // or it is not addressable.
   225  func (f flag) mustBeAssignable() {
   226  	if f == 0 {
   227  		panic(&ValueError{methodName(), Invalid})
   228  	}
   229  	// Assignable if addressable and not read-only.
   230  	if f&flagRO != 0 {
   231  		panic("reflect: " + methodName() + " using value obtained using unexported field")
   232  	}
   233  	if f&flagAddr == 0 {
   234  		panic("reflect: " + methodName() + " using unaddressable value")
   235  	}
   236  }
   237  
   238  // Addr returns a pointer value representing the address of v.
   239  // It panics if CanAddr() returns false.
   240  // Addr is typically used to obtain a pointer to a struct field
   241  // or slice element in order to call a method that requires a
   242  // pointer receiver.
   243  func (v Value) Addr() Value {
   244  	if v.flag&flagAddr == 0 {
   245  		panic("reflect.Value.Addr of unaddressable value")
   246  	}
   247  	return Value{v.typ.ptrTo(), v.ptr, v.flag.ro() | flag(Ptr)}
   248  }
   249  
   250  // Bool returns v's underlying value.
   251  // It panics if v's kind is not Bool.
   252  func (v Value) Bool() bool {
   253  	v.mustBe(Bool)
   254  	return *(*bool)(v.ptr)
   255  }
   256  
   257  // Bytes returns v's underlying value.
   258  // It panics if v's underlying value is not a slice of bytes.
   259  func (v Value) Bytes() []byte {
   260  	v.mustBe(Slice)
   261  	if v.typ.Elem().Kind() != Uint8 {
   262  		panic("reflect.Value.Bytes of non-byte slice")
   263  	}
   264  	// Slice is always bigger than a word; assume flagIndir.
   265  	return *(*[]byte)(v.ptr)
   266  }
   267  
   268  // runes returns v's underlying value.
   269  // It panics if v's underlying value is not a slice of runes (int32s).
   270  func (v Value) runes() []rune {
   271  	v.mustBe(Slice)
   272  	if v.typ.Elem().Kind() != Int32 {
   273  		panic("reflect.Value.Bytes of non-rune slice")
   274  	}
   275  	// Slice is always bigger than a word; assume flagIndir.
   276  	return *(*[]rune)(v.ptr)
   277  }
   278  
   279  // CanAddr reports whether the value's address can be obtained with Addr.
   280  // Such values are called addressable. A value is addressable if it is
   281  // an element of a slice, an element of an addressable array,
   282  // a field of an addressable struct, or the result of dereferencing a pointer.
   283  // If CanAddr returns false, calling Addr will panic.
   284  func (v Value) CanAddr() bool {
   285  	return v.flag&flagAddr != 0
   286  }
   287  
   288  // CanSet reports whether the value of v can be changed.
   289  // A Value can be changed only if it is addressable and was not
   290  // obtained by the use of unexported struct fields.
   291  // If CanSet returns false, calling Set or any type-specific
   292  // setter (e.g., SetBool, SetInt) will panic.
   293  func (v Value) CanSet() bool {
   294  	return v.flag&(flagAddr|flagRO) == flagAddr
   295  }
   296  
   297  // Call calls the function v with the input arguments in.
   298  // For example, if len(in) == 3, v.Call(in) represents the Go call v(in[0], in[1], in[2]).
   299  // Call panics if v's Kind is not Func.
   300  // It returns the output results as Values.
   301  // As in Go, each input argument must be assignable to the
   302  // type of the function's corresponding input parameter.
   303  // If v is a variadic function, Call creates the variadic slice parameter
   304  // itself, copying in the corresponding values.
   305  func (v Value) Call(in []Value) []Value {
   306  	v.mustBe(Func)
   307  	v.mustBeExported()
   308  	return v.call("Call", in)
   309  }
   310  
   311  // CallSlice calls the variadic function v with the input arguments in,
   312  // assigning the slice in[len(in)-1] to v's final variadic argument.
   313  // For example, if len(in) == 3, v.CallSlice(in) represents the Go call v(in[0], in[1], in[2]...).
   314  // CallSlice panics if v's Kind is not Func or if v is not variadic.
   315  // It returns the output results as Values.
   316  // As in Go, each input argument must be assignable to the
   317  // type of the function's corresponding input parameter.
   318  func (v Value) CallSlice(in []Value) []Value {
   319  	v.mustBe(Func)
   320  	v.mustBeExported()
   321  	return v.call("CallSlice", in)
   322  }
   323  
   324  var callGC bool // for testing; see TestCallMethodJump
   325  
   326  func (v Value) call(op string, in []Value) []Value {
   327  	// Get function pointer, type.
   328  	t := (*funcType)(unsafe.Pointer(v.typ))
   329  	var (
   330  		fn       unsafe.Pointer
   331  		rcvr     Value
   332  		rcvrtype *rtype
   333  	)
   334  	if v.flag&flagMethod != 0 {
   335  		rcvr = v
   336  		rcvrtype, t, fn = methodReceiver(op, v, int(v.flag)>>flagMethodShift)
   337  	} else if v.flag&flagIndir != 0 {
   338  		fn = *(*unsafe.Pointer)(v.ptr)
   339  	} else {
   340  		fn = v.ptr
   341  	}
   342  
   343  	if fn == nil {
   344  		panic("reflect.Value.Call: call of nil function")
   345  	}
   346  
   347  	isSlice := op == "CallSlice"
   348  	n := t.NumIn()
   349  	if isSlice {
   350  		if !t.IsVariadic() {
   351  			panic("reflect: CallSlice of non-variadic function")
   352  		}
   353  		if len(in) < n {
   354  			panic("reflect: CallSlice with too few input arguments")
   355  		}
   356  		if len(in) > n {
   357  			panic("reflect: CallSlice with too many input arguments")
   358  		}
   359  	} else {
   360  		if t.IsVariadic() {
   361  			n--
   362  		}
   363  		if len(in) < n {
   364  			panic("reflect: Call with too few input arguments")
   365  		}
   366  		if !t.IsVariadic() && len(in) > n {
   367  			panic("reflect: Call with too many input arguments")
   368  		}
   369  	}
   370  	for _, x := range in {
   371  		if x.Kind() == Invalid {
   372  			panic("reflect: " + op + " using zero Value argument")
   373  		}
   374  	}
   375  	for i := 0; i < n; i++ {
   376  		if xt, targ := in[i].Type(), t.In(i); !xt.AssignableTo(targ) {
   377  			panic("reflect: " + op + " using " + xt.String() + " as type " + targ.String())
   378  		}
   379  	}
   380  	if !isSlice && t.IsVariadic() {
   381  		// prepare slice for remaining values
   382  		m := len(in) - n
   383  		slice := MakeSlice(t.In(n), m, m)
   384  		elem := t.In(n).Elem()
   385  		for i := 0; i < m; i++ {
   386  			x := in[n+i]
   387  			if xt := x.Type(); !xt.AssignableTo(elem) {
   388  				panic("reflect: cannot use " + xt.String() + " as type " + elem.String() + " in " + op)
   389  			}
   390  			slice.Index(i).Set(x)
   391  		}
   392  		origIn := in
   393  		in = make([]Value, n+1)
   394  		copy(in[:n], origIn)
   395  		in[n] = slice
   396  	}
   397  
   398  	nin := len(in)
   399  	if nin != t.NumIn() {
   400  		panic("reflect.Value.Call: wrong argument count")
   401  	}
   402  	nout := t.NumOut()
   403  
   404  	// Compute frame type.
   405  	frametype, _, retOffset, _, framePool := funcLayout(t, rcvrtype)
   406  
   407  	// Allocate a chunk of memory for frame.
   408  	var args unsafe.Pointer
   409  	if nout == 0 {
   410  		args = framePool.Get().(unsafe.Pointer)
   411  	} else {
   412  		// Can't use pool if the function has return values.
   413  		// We will leak pointer to args in ret, so its lifetime is not scoped.
   414  		args = unsafe_New(frametype)
   415  	}
   416  	off := uintptr(0)
   417  
   418  	// Copy inputs into args.
   419  	if rcvrtype != nil {
   420  		storeRcvr(rcvr, args)
   421  		off = ptrSize
   422  	}
   423  	for i, v := range in {
   424  		v.mustBeExported()
   425  		targ := t.In(i).(*rtype)
   426  		a := uintptr(targ.align)
   427  		off = (off + a - 1) &^ (a - 1)
   428  		n := targ.size
   429  		if n == 0 {
   430  			// Not safe to compute args+off pointing at 0 bytes,
   431  			// because that might point beyond the end of the frame,
   432  			// but we still need to call assignTo to check assignability.
   433  			v.assignTo("reflect.Value.Call", targ, nil)
   434  			continue
   435  		}
   436  		addr := add(args, off, "n > 0")
   437  		v = v.assignTo("reflect.Value.Call", targ, addr)
   438  		if v.flag&flagIndir != 0 {
   439  			typedmemmove(targ, addr, v.ptr)
   440  		} else {
   441  			*(*unsafe.Pointer)(addr) = v.ptr
   442  		}
   443  		off += n
   444  	}
   445  
   446  	// Call.
   447  	call(frametype, fn, args, uint32(frametype.size), uint32(retOffset))
   448  
   449  	// For testing; see TestCallMethodJump.
   450  	if callGC {
   451  		runtime.GC()
   452  	}
   453  
   454  	var ret []Value
   455  	if nout == 0 {
   456  		typedmemclr(frametype, args)
   457  		framePool.Put(args)
   458  	} else {
   459  		// Zero the now unused input area of args,
   460  		// because the Values returned by this function contain pointers to the args object,
   461  		// and will thus keep the args object alive indefinitely.
   462  		typedmemclrpartial(frametype, args, 0, retOffset)
   463  
   464  		// Wrap Values around return values in args.
   465  		ret = make([]Value, nout)
   466  		off = retOffset
   467  		for i := 0; i < nout; i++ {
   468  			tv := t.Out(i)
   469  			a := uintptr(tv.Align())
   470  			off = (off + a - 1) &^ (a - 1)
   471  			if tv.Size() != 0 {
   472  				fl := flagIndir | flag(tv.Kind())
   473  				ret[i] = Value{tv.common(), add(args, off, "tv.Size() != 0"), fl}
   474  				// Note: this does introduce false sharing between results -
   475  				// if any result is live, they are all live.
   476  				// (And the space for the args is live as well, but as we've
   477  				// cleared that space it isn't as big a deal.)
   478  			} else {
   479  				// For zero-sized return value, args+off may point to the next object.
   480  				// In this case, return the zero value instead.
   481  				ret[i] = Zero(tv)
   482  			}
   483  			off += tv.Size()
   484  		}
   485  	}
   486  
   487  	return ret
   488  }
   489  
   490  // callReflect is the call implementation used by a function
   491  // returned by MakeFunc. In many ways it is the opposite of the
   492  // method Value.call above. The method above converts a call using Values
   493  // into a call of a function with a concrete argument frame, while
   494  // callReflect converts a call of a function with a concrete argument
   495  // frame into a call using Values.
   496  // It is in this file so that it can be next to the call method above.
   497  // The remainder of the MakeFunc implementation is in makefunc.go.
   498  //
   499  // NOTE: This function must be marked as a "wrapper" in the generated code,
   500  // so that the linker can make it work correctly for panic and recover.
   501  // The gc compilers know to do that for the name "reflect.callReflect".
   502  //
   503  // ctxt is the "closure" generated by MakeFunc.
   504  // frame is a pointer to the arguments to that closure on the stack.
   505  // retValid points to a boolean which should be set when the results
   506  // section of frame is set.
   507  func callReflect(ctxt *makeFuncImpl, frame unsafe.Pointer, retValid *bool) {
   508  	ftyp := ctxt.ftyp
   509  	f := ctxt.fn
   510  
   511  	// Copy argument frame into Values.
   512  	ptr := frame
   513  	off := uintptr(0)
   514  	in := make([]Value, 0, int(ftyp.inCount))
   515  	for _, typ := range ftyp.in() {
   516  		off += -off & uintptr(typ.align-1)
   517  		v := Value{typ, nil, flag(typ.Kind())}
   518  		if ifaceIndir(typ) {
   519  			// value cannot be inlined in interface data.
   520  			// Must make a copy, because f might keep a reference to it,
   521  			// and we cannot let f keep a reference to the stack frame
   522  			// after this function returns, not even a read-only reference.
   523  			v.ptr = unsafe_New(typ)
   524  			if typ.size > 0 {
   525  				typedmemmove(typ, v.ptr, add(ptr, off, "typ.size > 0"))
   526  			}
   527  			v.flag |= flagIndir
   528  		} else {
   529  			v.ptr = *(*unsafe.Pointer)(add(ptr, off, "1-ptr"))
   530  		}
   531  		in = append(in, v)
   532  		off += typ.size
   533  	}
   534  
   535  	// Call underlying function.
   536  	out := f(in)
   537  	numOut := ftyp.NumOut()
   538  	if len(out) != numOut {
   539  		panic("reflect: wrong return count from function created by MakeFunc")
   540  	}
   541  
   542  	// Copy results back into argument frame.
   543  	if numOut > 0 {
   544  		off += -off & (ptrSize - 1)
   545  		if runtime.GOARCH == "amd64p32" {
   546  			off = align(off, 8)
   547  		}
   548  		for i, typ := range ftyp.out() {
   549  			v := out[i]
   550  			if v.typ != typ {
   551  				panic("reflect: function created by MakeFunc using " + funcName(f) +
   552  					" returned wrong type: have " +
   553  					out[i].typ.String() + " for " + typ.String())
   554  			}
   555  			if v.flag&flagRO != 0 {
   556  				panic("reflect: function created by MakeFunc using " + funcName(f) +
   557  					" returned value obtained from unexported field")
   558  			}
   559  			off += -off & uintptr(typ.align-1)
   560  			if typ.size == 0 {
   561  				continue
   562  			}
   563  			addr := add(ptr, off, "typ.size > 0")
   564  			if v.flag&flagIndir != 0 {
   565  				typedmemmove(typ, addr, v.ptr)
   566  			} else {
   567  				*(*unsafe.Pointer)(addr) = v.ptr
   568  			}
   569  			off += typ.size
   570  		}
   571  	}
   572  
   573  	// Announce that the return values are valid.
   574  	// After this point the runtime can depend on the return values being valid.
   575  	*retValid = true
   576  
   577  	// We have to make sure that the out slice lives at least until
   578  	// the runtime knows the return values are valid. Otherwise, the
   579  	// return values might not be scanned by anyone during a GC.
   580  	// (out would be dead, and the return slots not yet alive.)
   581  	runtime.KeepAlive(out)
   582  
   583  	// runtime.getArgInfo expects to be able to find ctxt on the
   584  	// stack when it finds our caller, makeFuncStub. Make sure it
   585  	// doesn't get garbage collected.
   586  	runtime.KeepAlive(ctxt)
   587  }
   588  
   589  // methodReceiver returns information about the receiver
   590  // described by v. The Value v may or may not have the
   591  // flagMethod bit set, so the kind cached in v.flag should
   592  // not be used.
   593  // The return value rcvrtype gives the method's actual receiver type.
   594  // The return value t gives the method type signature (without the receiver).
   595  // The return value fn is a pointer to the method code.
   596  func methodReceiver(op string, v Value, methodIndex int) (rcvrtype *rtype, t *funcType, fn unsafe.Pointer) {
   597  	i := methodIndex
   598  	if v.typ.Kind() == Interface {
   599  		tt := (*interfaceType)(unsafe.Pointer(v.typ))
   600  		if uint(i) >= uint(len(tt.methods)) {
   601  			panic("reflect: internal error: invalid method index")
   602  		}
   603  		m := &tt.methods[i]
   604  		if !tt.nameOff(m.name).isExported() {
   605  			panic("reflect: " + op + " of unexported method")
   606  		}
   607  		iface := (*nonEmptyInterface)(v.ptr)
   608  		if iface.itab == nil {
   609  			panic("reflect: " + op + " of method on nil interface value")
   610  		}
   611  		rcvrtype = iface.itab.typ
   612  		fn = unsafe.Pointer(&iface.itab.fun[i])
   613  		t = (*funcType)(unsafe.Pointer(tt.typeOff(m.typ)))
   614  	} else {
   615  		rcvrtype = v.typ
   616  		ms := v.typ.exportedMethods()
   617  		if uint(i) >= uint(len(ms)) {
   618  			panic("reflect: internal error: invalid method index")
   619  		}
   620  		m := ms[i]
   621  		if !v.typ.nameOff(m.name).isExported() {
   622  			panic("reflect: " + op + " of unexported method")
   623  		}
   624  		ifn := v.typ.textOff(m.ifn)
   625  		fn = unsafe.Pointer(&ifn)
   626  		t = (*funcType)(unsafe.Pointer(v.typ.typeOff(m.mtyp)))
   627  	}
   628  	return
   629  }
   630  
   631  // v is a method receiver. Store at p the word which is used to
   632  // encode that receiver at the start of the argument list.
   633  // Reflect uses the "interface" calling convention for
   634  // methods, which always uses one word to record the receiver.
   635  func storeRcvr(v Value, p unsafe.Pointer) {
   636  	t := v.typ
   637  	if t.Kind() == Interface {
   638  		// the interface data word becomes the receiver word
   639  		iface := (*nonEmptyInterface)(v.ptr)
   640  		*(*unsafe.Pointer)(p) = iface.word
   641  	} else if v.flag&flagIndir != 0 && !ifaceIndir(t) {
   642  		*(*unsafe.Pointer)(p) = *(*unsafe.Pointer)(v.ptr)
   643  	} else {
   644  		*(*unsafe.Pointer)(p) = v.ptr
   645  	}
   646  }
   647  
   648  // align returns the result of rounding x up to a multiple of n.
   649  // n must be a power of two.
   650  func align(x, n uintptr) uintptr {
   651  	return (x + n - 1) &^ (n - 1)
   652  }
   653  
   654  // callMethod is the call implementation used by a function returned
   655  // by makeMethodValue (used by v.Method(i).Interface()).
   656  // It is a streamlined version of the usual reflect call: the caller has
   657  // already laid out the argument frame for us, so we don't have
   658  // to deal with individual Values for each argument.
   659  // It is in this file so that it can be next to the two similar functions above.
   660  // The remainder of the makeMethodValue implementation is in makefunc.go.
   661  //
   662  // NOTE: This function must be marked as a "wrapper" in the generated code,
   663  // so that the linker can make it work correctly for panic and recover.
   664  // The gc compilers know to do that for the name "reflect.callMethod".
   665  //
   666  // ctxt is the "closure" generated by makeVethodValue.
   667  // frame is a pointer to the arguments to that closure on the stack.
   668  // retValid points to a boolean which should be set when the results
   669  // section of frame is set.
   670  func callMethod(ctxt *methodValue, frame unsafe.Pointer, retValid *bool) {
   671  	rcvr := ctxt.rcvr
   672  	rcvrtype, t, fn := methodReceiver("call", rcvr, ctxt.method)
   673  	frametype, argSize, retOffset, _, framePool := funcLayout(t, rcvrtype)
   674  
   675  	// Make a new frame that is one word bigger so we can store the receiver.
   676  	// This space is used for both arguments and return values.
   677  	scratch := framePool.Get().(unsafe.Pointer)
   678  
   679  	// Copy in receiver and rest of args.
   680  	// Avoid constructing out-of-bounds pointers if there are no args.
   681  	storeRcvr(rcvr, scratch)
   682  	if argSize-ptrSize > 0 {
   683  		typedmemmovepartial(frametype, add(scratch, ptrSize, "argSize > ptrSize"), frame, ptrSize, argSize-ptrSize)
   684  	}
   685  
   686  	// Call.
   687  	// Call copies the arguments from scratch to the stack, calls fn,
   688  	// and then copies the results back into scratch.
   689  	call(frametype, fn, scratch, uint32(frametype.size), uint32(retOffset))
   690  
   691  	// Copy return values. On amd64p32, the beginning of return values
   692  	// is 64-bit aligned, so the caller's frame layout (which doesn't have
   693  	// a receiver) is different from the layout of the fn call, which has
   694  	// a receiver.
   695  	// Ignore any changes to args and just copy return values.
   696  	// Avoid constructing out-of-bounds pointers if there are no return values.
   697  	if frametype.size-retOffset > 0 {
   698  		callerRetOffset := retOffset - ptrSize
   699  		if runtime.GOARCH == "amd64p32" {
   700  			callerRetOffset = align(argSize-ptrSize, 8)
   701  		}
   702  		// This copies to the stack. Write barriers are not needed.
   703  		memmove(add(frame, callerRetOffset, "frametype.size > retOffset"),
   704  			add(scratch, retOffset, "frametype.size > retOffset"),
   705  			frametype.size-retOffset)
   706  	}
   707  
   708  	// Tell the runtime it can now depend on the return values
   709  	// being properly initialized.
   710  	*retValid = true
   711  
   712  	// Clear the scratch space and put it back in the pool.
   713  	// This must happen after the statement above, so that the return
   714  	// values will always be scanned by someone.
   715  	typedmemclr(frametype, scratch)
   716  	framePool.Put(scratch)
   717  
   718  	// See the comment in callReflect.
   719  	runtime.KeepAlive(ctxt)
   720  }
   721  
   722  // funcName returns the name of f, for use in error messages.
   723  func funcName(f func([]Value) []Value) string {
   724  	pc := *(*uintptr)(unsafe.Pointer(&f))
   725  	rf := runtime.FuncForPC(pc)
   726  	if rf != nil {
   727  		return rf.Name()
   728  	}
   729  	return "closure"
   730  }
   731  
   732  // Cap returns v's capacity.
   733  // It panics if v's Kind is not Array, Chan, or Slice.
   734  func (v Value) Cap() int {
   735  	k := v.kind()
   736  	switch k {
   737  	case Array:
   738  		return v.typ.Len()
   739  	case Chan:
   740  		return chancap(v.pointer())
   741  	case Slice:
   742  		// Slice is always bigger than a word; assume flagIndir.
   743  		return (*sliceHeader)(v.ptr).Cap
   744  	}
   745  	panic(&ValueError{"reflect.Value.Cap", v.kind()})
   746  }
   747  
   748  // Close closes the channel v.
   749  // It panics if v's Kind is not Chan.
   750  func (v Value) Close() {
   751  	v.mustBe(Chan)
   752  	v.mustBeExported()
   753  	chanclose(v.pointer())
   754  }
   755  
   756  // Complex returns v's underlying value, as a complex128.
   757  // It panics if v's Kind is not Complex64 or Complex128
   758  func (v Value) Complex() complex128 {
   759  	k := v.kind()
   760  	switch k {
   761  	case Complex64:
   762  		return complex128(*(*complex64)(v.ptr))
   763  	case Complex128:
   764  		return *(*complex128)(v.ptr)
   765  	}
   766  	panic(&ValueError{"reflect.Value.Complex", v.kind()})
   767  }
   768  
   769  // Elem returns the value that the interface v contains
   770  // or that the pointer v points to.
   771  // It panics if v's Kind is not Interface or Ptr.
   772  // It returns the zero Value if v is nil.
   773  func (v Value) Elem() Value {
   774  	k := v.kind()
   775  	switch k {
   776  	case Interface:
   777  		var eface interface{}
   778  		if v.typ.NumMethod() == 0 {
   779  			eface = *(*interface{})(v.ptr)
   780  		} else {
   781  			eface = (interface{})(*(*interface {
   782  				M()
   783  			})(v.ptr))
   784  		}
   785  		x := unpackEface(eface)
   786  		if x.flag != 0 {
   787  			x.flag |= v.flag.ro()
   788  		}
   789  		return x
   790  	case Ptr:
   791  		ptr := v.ptr
   792  		if v.flag&flagIndir != 0 {
   793  			ptr = *(*unsafe.Pointer)(ptr)
   794  		}
   795  		// The returned value's address is v's value.
   796  		if ptr == nil {
   797  			return Value{}
   798  		}
   799  		tt := (*ptrType)(unsafe.Pointer(v.typ))
   800  		typ := tt.elem
   801  		fl := v.flag&flagRO | flagIndir | flagAddr
   802  		fl |= flag(typ.Kind())
   803  		return Value{typ, ptr, fl}
   804  	}
   805  	panic(&ValueError{"reflect.Value.Elem", v.kind()})
   806  }
   807  
   808  // Field returns the i'th field of the struct v.
   809  // It panics if v's Kind is not Struct or i is out of range.
   810  func (v Value) Field(i int) Value {
   811  	if v.kind() != Struct {
   812  		panic(&ValueError{"reflect.Value.Field", v.kind()})
   813  	}
   814  	tt := (*structType)(unsafe.Pointer(v.typ))
   815  	if uint(i) >= uint(len(tt.fields)) {
   816  		panic("reflect: Field index out of range")
   817  	}
   818  	field := &tt.fields[i]
   819  	typ := field.typ
   820  
   821  	// Inherit permission bits from v, but clear flagEmbedRO.
   822  	fl := v.flag&(flagStickyRO|flagIndir|flagAddr) | flag(typ.Kind())
   823  	// Using an unexported field forces flagRO.
   824  	if !field.name.isExported() {
   825  		if field.embedded() {
   826  			fl |= flagEmbedRO
   827  		} else {
   828  			fl |= flagStickyRO
   829  		}
   830  	}
   831  	// Either flagIndir is set and v.ptr points at struct,
   832  	// or flagIndir is not set and v.ptr is the actual struct data.
   833  	// In the former case, we want v.ptr + offset.
   834  	// In the latter case, we must have field.offset = 0,
   835  	// so v.ptr + field.offset is still the correct address.
   836  	ptr := add(v.ptr, field.offset(), "same as non-reflect &v.field")
   837  	return Value{typ, ptr, fl}
   838  }
   839  
   840  // FieldByIndex returns the nested field corresponding to index.
   841  // It panics if v's Kind is not struct.
   842  func (v Value) FieldByIndex(index []int) Value {
   843  	if len(index) == 1 {
   844  		return v.Field(index[0])
   845  	}
   846  	v.mustBe(Struct)
   847  	for i, x := range index {
   848  		if i > 0 {
   849  			if v.Kind() == Ptr && v.typ.Elem().Kind() == Struct {
   850  				if v.IsNil() {
   851  					panic("reflect: indirection through nil pointer to embedded struct")
   852  				}
   853  				v = v.Elem()
   854  			}
   855  		}
   856  		v = v.Field(x)
   857  	}
   858  	return v
   859  }
   860  
   861  // FieldByName returns the struct field with the given name.
   862  // It returns the zero Value if no field was found.
   863  // It panics if v's Kind is not struct.
   864  func (v Value) FieldByName(name string) Value {
   865  	v.mustBe(Struct)
   866  	if f, ok := v.typ.FieldByName(name); ok {
   867  		return v.FieldByIndex(f.Index)
   868  	}
   869  	return Value{}
   870  }
   871  
   872  // FieldByNameFunc returns the struct field with a name
   873  // that satisfies the match function.
   874  // It panics if v's Kind is not struct.
   875  // It returns the zero Value if no field was found.
   876  func (v Value) FieldByNameFunc(match func(string) bool) Value {
   877  	if f, ok := v.typ.FieldByNameFunc(match); ok {
   878  		return v.FieldByIndex(f.Index)
   879  	}
   880  	return Value{}
   881  }
   882  
   883  // Float returns v's underlying value, as a float64.
   884  // It panics if v's Kind is not Float32 or Float64
   885  func (v Value) Float() float64 {
   886  	k := v.kind()
   887  	switch k {
   888  	case Float32:
   889  		return float64(*(*float32)(v.ptr))
   890  	case Float64:
   891  		return *(*float64)(v.ptr)
   892  	}
   893  	panic(&ValueError{"reflect.Value.Float", v.kind()})
   894  }
   895  
   896  var uint8Type = TypeOf(uint8(0)).(*rtype)
   897  
   898  // Index returns v's i'th element.
   899  // It panics if v's Kind is not Array, Slice, or String or i is out of range.
   900  func (v Value) Index(i int) Value {
   901  	switch v.kind() {
   902  	case Array:
   903  		tt := (*arrayType)(unsafe.Pointer(v.typ))
   904  		if uint(i) >= uint(tt.len) {
   905  			panic("reflect: array index out of range")
   906  		}
   907  		typ := tt.elem
   908  		offset := uintptr(i) * typ.size
   909  
   910  		// Either flagIndir is set and v.ptr points at array,
   911  		// or flagIndir is not set and v.ptr is the actual array data.
   912  		// In the former case, we want v.ptr + offset.
   913  		// In the latter case, we must be doing Index(0), so offset = 0,
   914  		// so v.ptr + offset is still the correct address.
   915  		val := add(v.ptr, offset, "same as &v[i], i < tt.len")
   916  		fl := v.flag&(flagIndir|flagAddr) | v.flag.ro() | flag(typ.Kind()) // bits same as overall array
   917  		return Value{typ, val, fl}
   918  
   919  	case Slice:
   920  		// Element flag same as Elem of Ptr.
   921  		// Addressable, indirect, possibly read-only.
   922  		s := (*sliceHeader)(v.ptr)
   923  		if uint(i) >= uint(s.Len) {
   924  			panic("reflect: slice index out of range")
   925  		}
   926  		tt := (*sliceType)(unsafe.Pointer(v.typ))
   927  		typ := tt.elem
   928  		val := arrayAt(s.Data, i, typ.size, "i < s.Len")
   929  		fl := flagAddr | flagIndir | v.flag.ro() | flag(typ.Kind())
   930  		return Value{typ, val, fl}
   931  
   932  	case String:
   933  		s := (*stringHeader)(v.ptr)
   934  		if uint(i) >= uint(s.Len) {
   935  			panic("reflect: string index out of range")
   936  		}
   937  		p := arrayAt(s.Data, i, 1, "i < s.Len")
   938  		fl := v.flag.ro() | flag(Uint8) | flagIndir
   939  		return Value{uint8Type, p, fl}
   940  	}
   941  	panic(&ValueError{"reflect.Value.Index", v.kind()})
   942  }
   943  
   944  // Int returns v's underlying value, as an int64.
   945  // It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64.
   946  func (v Value) Int() int64 {
   947  	k := v.kind()
   948  	p := v.ptr
   949  	switch k {
   950  	case Int:
   951  		return int64(*(*int)(p))
   952  	case Int8:
   953  		return int64(*(*int8)(p))
   954  	case Int16:
   955  		return int64(*(*int16)(p))
   956  	case Int32:
   957  		return int64(*(*int32)(p))
   958  	case Int64:
   959  		return *(*int64)(p)
   960  	}
   961  	panic(&ValueError{"reflect.Value.Int", v.kind()})
   962  }
   963  
   964  // CanInterface reports whether Interface can be used without panicking.
   965  func (v Value) CanInterface() bool {
   966  	if v.flag == 0 {
   967  		panic(&ValueError{"reflect.Value.CanInterface", Invalid})
   968  	}
   969  	return v.flag&flagRO == 0
   970  }
   971  
   972  // Interface returns v's current value as an interface{}.
   973  // It is equivalent to:
   974  //	var i interface{} = (v's underlying value)
   975  // It panics if the Value was obtained by accessing
   976  // unexported struct fields.
   977  func (v Value) Interface() (i interface{}) {
   978  	return valueInterface(v, true)
   979  }
   980  
   981  func valueInterface(v Value, safe bool) interface{} {
   982  	if v.flag == 0 {
   983  		panic(&ValueError{"reflect.Value.Interface", 0})
   984  	}
   985  	if safe && v.flag&flagRO != 0 {
   986  		// Do not allow access to unexported values via Interface,
   987  		// because they might be pointers that should not be
   988  		// writable or methods or function that should not be callable.
   989  		panic("reflect.Value.Interface: cannot return value obtained from unexported field or method")
   990  	}
   991  	if v.flag&flagMethod != 0 {
   992  		v = makeMethodValue("Interface", v)
   993  	}
   994  
   995  	if v.kind() == Interface {
   996  		// Special case: return the element inside the interface.
   997  		// Empty interface has one layout, all interfaces with
   998  		// methods have a second layout.
   999  		if v.NumMethod() == 0 {
  1000  			return *(*interface{})(v.ptr)
  1001  		}
  1002  		return *(*interface {
  1003  			M()
  1004  		})(v.ptr)
  1005  	}
  1006  
  1007  	// TODO: pass safe to packEface so we don't need to copy if safe==true?
  1008  	return packEface(v)
  1009  }
  1010  
  1011  // InterfaceData returns the interface v's value as a uintptr pair.
  1012  // It panics if v's Kind is not Interface.
  1013  func (v Value) InterfaceData() [2]uintptr {
  1014  	// TODO: deprecate this
  1015  	v.mustBe(Interface)
  1016  	// We treat this as a read operation, so we allow
  1017  	// it even for unexported data, because the caller
  1018  	// has to import "unsafe" to turn it into something
  1019  	// that can be abused.
  1020  	// Interface value is always bigger than a word; assume flagIndir.
  1021  	return *(*[2]uintptr)(v.ptr)
  1022  }
  1023  
  1024  // IsNil reports whether its argument v is nil. The argument must be
  1025  // a chan, func, interface, map, pointer, or slice value; if it is
  1026  // not, IsNil panics. Note that IsNil is not always equivalent to a
  1027  // regular comparison with nil in Go. For example, if v was created
  1028  // by calling ValueOf with an uninitialized interface variable i,
  1029  // i==nil will be true but v.IsNil will panic as v will be the zero
  1030  // Value.
  1031  func (v Value) IsNil() bool {
  1032  	k := v.kind()
  1033  	switch k {
  1034  	case Chan, Func, Map, Ptr:
  1035  		if v.flag&flagMethod != 0 {
  1036  			return false
  1037  		}
  1038  		ptr := v.ptr
  1039  		if v.flag&flagIndir != 0 {
  1040  			ptr = *(*unsafe.Pointer)(ptr)
  1041  		}
  1042  		return ptr == nil
  1043  	case Interface, Slice:
  1044  		// Both interface and slice are nil if first word is 0.
  1045  		// Both are always bigger than a word; assume flagIndir.
  1046  		return *(*unsafe.Pointer)(v.ptr) == nil
  1047  	}
  1048  	panic(&ValueError{"reflect.Value.IsNil", v.kind()})
  1049  }
  1050  
  1051  // IsValid reports whether v represents a value.
  1052  // It returns false if v is the zero Value.
  1053  // If IsValid returns false, all other methods except String panic.
  1054  // Most functions and methods never return an invalid value.
  1055  // If one does, its documentation states the conditions explicitly.
  1056  func (v Value) IsValid() bool {
  1057  	return v.flag != 0
  1058  }
  1059  
  1060  // Kind returns v's Kind.
  1061  // If v is the zero Value (IsValid returns false), Kind returns Invalid.
  1062  func (v Value) Kind() Kind {
  1063  	return v.kind()
  1064  }
  1065  
  1066  // Len returns v's length.
  1067  // It panics if v's Kind is not Array, Chan, Map, Slice, or String.
  1068  func (v Value) Len() int {
  1069  	k := v.kind()
  1070  	switch k {
  1071  	case Array:
  1072  		tt := (*arrayType)(unsafe.Pointer(v.typ))
  1073  		return int(tt.len)
  1074  	case Chan:
  1075  		return chanlen(v.pointer())
  1076  	case Map:
  1077  		return maplen(v.pointer())
  1078  	case Slice:
  1079  		// Slice is bigger than a word; assume flagIndir.
  1080  		return (*sliceHeader)(v.ptr).Len
  1081  	case String:
  1082  		// String is bigger than a word; assume flagIndir.
  1083  		return (*stringHeader)(v.ptr).Len
  1084  	}
  1085  	panic(&ValueError{"reflect.Value.Len", v.kind()})
  1086  }
  1087  
  1088  // MapIndex returns the value associated with key in the map v.
  1089  // It panics if v's Kind is not Map.
  1090  // It returns the zero Value if key is not found in the map or if v represents a nil map.
  1091  // As in Go, the key's value must be assignable to the map's key type.
  1092  func (v Value) MapIndex(key Value) Value {
  1093  	v.mustBe(Map)
  1094  	tt := (*mapType)(unsafe.Pointer(v.typ))
  1095  
  1096  	// Do not require key to be exported, so that DeepEqual
  1097  	// and other programs can use all the keys returned by
  1098  	// MapKeys as arguments to MapIndex. If either the map
  1099  	// or the key is unexported, though, the result will be
  1100  	// considered unexported. This is consistent with the
  1101  	// behavior for structs, which allow read but not write
  1102  	// of unexported fields.
  1103  	key = key.assignTo("reflect.Value.MapIndex", tt.key, nil)
  1104  
  1105  	var k unsafe.Pointer
  1106  	if key.flag&flagIndir != 0 {
  1107  		k = key.ptr
  1108  	} else {
  1109  		k = unsafe.Pointer(&key.ptr)
  1110  	}
  1111  	e := mapaccess(v.typ, v.pointer(), k)
  1112  	if e == nil {
  1113  		return Value{}
  1114  	}
  1115  	typ := tt.elem
  1116  	fl := (v.flag | key.flag).ro()
  1117  	fl |= flag(typ.Kind())
  1118  	if !ifaceIndir(typ) {
  1119  		return Value{typ, *(*unsafe.Pointer)(e), fl}
  1120  	}
  1121  	// Copy result so future changes to the map
  1122  	// won't change the underlying value.
  1123  	c := unsafe_New(typ)
  1124  	typedmemmove(typ, c, e)
  1125  	return Value{typ, c, fl | flagIndir}
  1126  }
  1127  
  1128  // MapKeys returns a slice containing all the keys present in the map,
  1129  // in unspecified order.
  1130  // It panics if v's Kind is not Map.
  1131  // It returns an empty slice if v represents a nil map.
  1132  func (v Value) MapKeys() []Value {
  1133  	v.mustBe(Map)
  1134  	tt := (*mapType)(unsafe.Pointer(v.typ))
  1135  	keyType := tt.key
  1136  
  1137  	fl := v.flag.ro() | flag(keyType.Kind())
  1138  
  1139  	m := v.pointer()
  1140  	mlen := int(0)
  1141  	if m != nil {
  1142  		mlen = maplen(m)
  1143  	}
  1144  	it := mapiterinit(v.typ, m)
  1145  	a := make([]Value, mlen)
  1146  	var i int
  1147  	for i = 0; i < len(a); i++ {
  1148  		key := mapiterkey(it)
  1149  		if key == nil {
  1150  			// Someone deleted an entry from the map since we
  1151  			// called maplen above. It's a data race, but nothing
  1152  			// we can do about it.
  1153  			break
  1154  		}
  1155  		if ifaceIndir(keyType) {
  1156  			// Copy result so future changes to the map
  1157  			// won't change the underlying value.
  1158  			c := unsafe_New(keyType)
  1159  			typedmemmove(keyType, c, key)
  1160  			a[i] = Value{keyType, c, fl | flagIndir}
  1161  		} else {
  1162  			a[i] = Value{keyType, *(*unsafe.Pointer)(key), fl}
  1163  		}
  1164  		mapiternext(it)
  1165  	}
  1166  	return a[:i]
  1167  }
  1168  
  1169  // Method returns a function value corresponding to v's i'th method.
  1170  // The arguments to a Call on the returned function should not include
  1171  // a receiver; the returned function will always use v as the receiver.
  1172  // Method panics if i is out of range or if v is a nil interface value.
  1173  func (v Value) Method(i int) Value {
  1174  	if v.typ == nil {
  1175  		panic(&ValueError{"reflect.Value.Method", Invalid})
  1176  	}
  1177  	if v.flag&flagMethod != 0 || uint(i) >= uint(v.typ.NumMethod()) {
  1178  		panic("reflect: Method index out of range")
  1179  	}
  1180  	if v.typ.Kind() == Interface && v.IsNil() {
  1181  		panic("reflect: Method on nil interface value")
  1182  	}
  1183  	fl := v.flag & (flagStickyRO | flagIndir) // Clear flagEmbedRO
  1184  	fl |= flag(Func)
  1185  	fl |= flag(i)<<flagMethodShift | flagMethod
  1186  	return Value{v.typ, v.ptr, fl}
  1187  }
  1188  
  1189  // NumMethod returns the number of exported methods in the value's method set.
  1190  func (v Value) NumMethod() int {
  1191  	if v.typ == nil {
  1192  		panic(&ValueError{"reflect.Value.NumMethod", Invalid})
  1193  	}
  1194  	if v.flag&flagMethod != 0 {
  1195  		return 0
  1196  	}
  1197  	return v.typ.NumMethod()
  1198  }
  1199  
  1200  // MethodByName returns a function value corresponding to the method
  1201  // of v with the given name.
  1202  // The arguments to a Call on the returned function should not include
  1203  // a receiver; the returned function will always use v as the receiver.
  1204  // It returns the zero Value if no method was found.
  1205  func (v Value) MethodByName(name string) Value {
  1206  	if v.typ == nil {
  1207  		panic(&ValueError{"reflect.Value.MethodByName", Invalid})
  1208  	}
  1209  	if v.flag&flagMethod != 0 {
  1210  		return Value{}
  1211  	}
  1212  	m, ok := v.typ.MethodByName(name)
  1213  	if !ok {
  1214  		return Value{}
  1215  	}
  1216  	return v.Method(m.Index)
  1217  }
  1218  
  1219  // NumField returns the number of fields in the struct v.
  1220  // It panics if v's Kind is not Struct.
  1221  func (v Value) NumField() int {
  1222  	v.mustBe(Struct)
  1223  	tt := (*structType)(unsafe.Pointer(v.typ))
  1224  	return len(tt.fields)
  1225  }
  1226  
  1227  // OverflowComplex reports whether the complex128 x cannot be represented by v's type.
  1228  // It panics if v's Kind is not Complex64 or Complex128.
  1229  func (v Value) OverflowComplex(x complex128) bool {
  1230  	k := v.kind()
  1231  	switch k {
  1232  	case Complex64:
  1233  		return overflowFloat32(real(x)) || overflowFloat32(imag(x))
  1234  	case Complex128:
  1235  		return false
  1236  	}
  1237  	panic(&ValueError{"reflect.Value.OverflowComplex", v.kind()})
  1238  }
  1239  
  1240  // OverflowFloat reports whether the float64 x cannot be represented by v's type.
  1241  // It panics if v's Kind is not Float32 or Float64.
  1242  func (v Value) OverflowFloat(x float64) bool {
  1243  	k := v.kind()
  1244  	switch k {
  1245  	case Float32:
  1246  		return overflowFloat32(x)
  1247  	case Float64:
  1248  		return false
  1249  	}
  1250  	panic(&ValueError{"reflect.Value.OverflowFloat", v.kind()})
  1251  }
  1252  
  1253  func overflowFloat32(x float64) bool {
  1254  	if x < 0 {
  1255  		x = -x
  1256  	}
  1257  	return math.MaxFloat32 < x && x <= math.MaxFloat64
  1258  }
  1259  
  1260  // OverflowInt reports whether the int64 x cannot be represented by v's type.
  1261  // It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64.
  1262  func (v Value) OverflowInt(x int64) bool {
  1263  	k := v.kind()
  1264  	switch k {
  1265  	case Int, Int8, Int16, Int32, Int64:
  1266  		bitSize := v.typ.size * 8
  1267  		trunc := (x << (64 - bitSize)) >> (64 - bitSize)
  1268  		return x != trunc
  1269  	}
  1270  	panic(&ValueError{"reflect.Value.OverflowInt", v.kind()})
  1271  }
  1272  
  1273  // OverflowUint reports whether the uint64 x cannot be represented by v's type.
  1274  // It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.
  1275  func (v Value) OverflowUint(x uint64) bool {
  1276  	k := v.kind()
  1277  	switch k {
  1278  	case Uint, Uintptr, Uint8, Uint16, Uint32, Uint64:
  1279  		bitSize := v.typ.size * 8
  1280  		trunc := (x << (64 - bitSize)) >> (64 - bitSize)
  1281  		return x != trunc
  1282  	}
  1283  	panic(&ValueError{"reflect.Value.OverflowUint", v.kind()})
  1284  }
  1285  
  1286  // Pointer returns v's value as a uintptr.
  1287  // It returns uintptr instead of unsafe.Pointer so that
  1288  // code using reflect cannot obtain unsafe.Pointers
  1289  // without importing the unsafe package explicitly.
  1290  // It panics if v's Kind is not Chan, Func, Map, Ptr, Slice, or UnsafePointer.
  1291  //
  1292  // If v's Kind is Func, the returned pointer is an underlying
  1293  // code pointer, but not necessarily enough to identify a
  1294  // single function uniquely. The only guarantee is that the
  1295  // result is zero if and only if v is a nil func Value.
  1296  //
  1297  // If v's Kind is Slice, the returned pointer is to the first
  1298  // element of the slice. If the slice is nil the returned value
  1299  // is 0.  If the slice is empty but non-nil the return value is non-zero.
  1300  func (v Value) Pointer() uintptr {
  1301  	// TODO: deprecate
  1302  	k := v.kind()
  1303  	switch k {
  1304  	case Chan, Map, Ptr, UnsafePointer:
  1305  		return uintptr(v.pointer())
  1306  	case Func:
  1307  		if v.flag&flagMethod != 0 {
  1308  			// As the doc comment says, the returned pointer is an
  1309  			// underlying code pointer but not necessarily enough to
  1310  			// identify a single function uniquely. All method expressions
  1311  			// created via reflect have the same underlying code pointer,
  1312  			// so their Pointers are equal. The function used here must
  1313  			// match the one used in makeMethodValue.
  1314  			f := methodValueCall
  1315  			return **(**uintptr)(unsafe.Pointer(&f))
  1316  		}
  1317  		p := v.pointer()
  1318  		// Non-nil func value points at data block.
  1319  		// First word of data block is actual code.
  1320  		if p != nil {
  1321  			p = *(*unsafe.Pointer)(p)
  1322  		}
  1323  		return uintptr(p)
  1324  
  1325  	case Slice:
  1326  		return (*SliceHeader)(v.ptr).Data
  1327  	}
  1328  	panic(&ValueError{"reflect.Value.Pointer", v.kind()})
  1329  }
  1330  
  1331  // Recv receives and returns a value from the channel v.
  1332  // It panics if v's Kind is not Chan.
  1333  // The receive blocks until a value is ready.
  1334  // The boolean value ok is true if the value x corresponds to a send
  1335  // on the channel, false if it is a zero value received because the channel is closed.
  1336  func (v Value) Recv() (x Value, ok bool) {
  1337  	v.mustBe(Chan)
  1338  	v.mustBeExported()
  1339  	return v.recv(false)
  1340  }
  1341  
  1342  // internal recv, possibly non-blocking (nb).
  1343  // v is known to be a channel.
  1344  func (v Value) recv(nb bool) (val Value, ok bool) {
  1345  	tt := (*chanType)(unsafe.Pointer(v.typ))
  1346  	if ChanDir(tt.dir)&RecvDir == 0 {
  1347  		panic("reflect: recv on send-only channel")
  1348  	}
  1349  	t := tt.elem
  1350  	val = Value{t, nil, flag(t.Kind())}
  1351  	var p unsafe.Pointer
  1352  	if ifaceIndir(t) {
  1353  		p = unsafe_New(t)
  1354  		val.ptr = p
  1355  		val.flag |= flagIndir
  1356  	} else {
  1357  		p = unsafe.Pointer(&val.ptr)
  1358  	}
  1359  	selected, ok := chanrecv(v.pointer(), nb, p)
  1360  	if !selected {
  1361  		val = Value{}
  1362  	}
  1363  	return
  1364  }
  1365  
  1366  // Send sends x on the channel v.
  1367  // It panics if v's kind is not Chan or if x's type is not the same type as v's element type.
  1368  // As in Go, x's value must be assignable to the channel's element type.
  1369  func (v Value) Send(x Value) {
  1370  	v.mustBe(Chan)
  1371  	v.mustBeExported()
  1372  	v.send(x, false)
  1373  }
  1374  
  1375  // internal send, possibly non-blocking.
  1376  // v is known to be a channel.
  1377  func (v Value) send(x Value, nb bool) (selected bool) {
  1378  	tt := (*chanType)(unsafe.Pointer(v.typ))
  1379  	if ChanDir(tt.dir)&SendDir == 0 {
  1380  		panic("reflect: send on recv-only channel")
  1381  	}
  1382  	x.mustBeExported()
  1383  	x = x.assignTo("reflect.Value.Send", tt.elem, nil)
  1384  	var p unsafe.Pointer
  1385  	if x.flag&flagIndir != 0 {
  1386  		p = x.ptr
  1387  	} else {
  1388  		p = unsafe.Pointer(&x.ptr)
  1389  	}
  1390  	return chansend(v.pointer(), p, nb)
  1391  }
  1392  
  1393  // Set assigns x to the value v.
  1394  // It panics if CanSet returns false.
  1395  // As in Go, x's value must be assignable to v's type.
  1396  func (v Value) Set(x Value) {
  1397  	v.mustBeAssignable()
  1398  	x.mustBeExported() // do not let unexported x leak
  1399  	var target unsafe.Pointer
  1400  	if v.kind() == Interface {
  1401  		target = v.ptr
  1402  	}
  1403  	x = x.assignTo("reflect.Set", v.typ, target)
  1404  	if x.flag&flagIndir != 0 {
  1405  		typedmemmove(v.typ, v.ptr, x.ptr)
  1406  	} else {
  1407  		*(*unsafe.Pointer)(v.ptr) = x.ptr
  1408  	}
  1409  }
  1410  
  1411  // SetBool sets v's underlying value.
  1412  // It panics if v's Kind is not Bool or if CanSet() is false.
  1413  func (v Value) SetBool(x bool) {
  1414  	v.mustBeAssignable()
  1415  	v.mustBe(Bool)
  1416  	*(*bool)(v.ptr) = x
  1417  }
  1418  
  1419  // SetBytes sets v's underlying value.
  1420  // It panics if v's underlying value is not a slice of bytes.
  1421  func (v Value) SetBytes(x []byte) {
  1422  	v.mustBeAssignable()
  1423  	v.mustBe(Slice)
  1424  	if v.typ.Elem().Kind() != Uint8 {
  1425  		panic("reflect.Value.SetBytes of non-byte slice")
  1426  	}
  1427  	*(*[]byte)(v.ptr) = x
  1428  }
  1429  
  1430  // setRunes sets v's underlying value.
  1431  // It panics if v's underlying value is not a slice of runes (int32s).
  1432  func (v Value) setRunes(x []rune) {
  1433  	v.mustBeAssignable()
  1434  	v.mustBe(Slice)
  1435  	if v.typ.Elem().Kind() != Int32 {
  1436  		panic("reflect.Value.setRunes of non-rune slice")
  1437  	}
  1438  	*(*[]rune)(v.ptr) = x
  1439  }
  1440  
  1441  // SetComplex sets v's underlying value to x.
  1442  // It panics if v's Kind is not Complex64 or Complex128, or if CanSet() is false.
  1443  func (v Value) SetComplex(x complex128) {
  1444  	v.mustBeAssignable()
  1445  	switch k := v.kind(); k {
  1446  	default:
  1447  		panic(&ValueError{"reflect.Value.SetComplex", v.kind()})
  1448  	case Complex64:
  1449  		*(*complex64)(v.ptr) = complex64(x)
  1450  	case Complex128:
  1451  		*(*complex128)(v.ptr) = x
  1452  	}
  1453  }
  1454  
  1455  // SetFloat sets v's underlying value to x.
  1456  // It panics if v's Kind is not Float32 or Float64, or if CanSet() is false.
  1457  func (v Value) SetFloat(x float64) {
  1458  	v.mustBeAssignable()
  1459  	switch k := v.kind(); k {
  1460  	default:
  1461  		panic(&ValueError{"reflect.Value.SetFloat", v.kind()})
  1462  	case Float32:
  1463  		*(*float32)(v.ptr) = float32(x)
  1464  	case Float64:
  1465  		*(*float64)(v.ptr) = x
  1466  	}
  1467  }
  1468  
  1469  // SetInt sets v's underlying value to x.
  1470  // It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64, or if CanSet() is false.
  1471  func (v Value) SetInt(x int64) {
  1472  	v.mustBeAssignable()
  1473  	switch k := v.kind(); k {
  1474  	default:
  1475  		panic(&ValueError{"reflect.Value.SetInt", v.kind()})
  1476  	case Int:
  1477  		*(*int)(v.ptr) = int(x)
  1478  	case Int8:
  1479  		*(*int8)(v.ptr) = int8(x)
  1480  	case Int16:
  1481  		*(*int16)(v.ptr) = int16(x)
  1482  	case Int32:
  1483  		*(*int32)(v.ptr) = int32(x)
  1484  	case Int64:
  1485  		*(*int64)(v.ptr) = x
  1486  	}
  1487  }
  1488  
  1489  // SetLen sets v's length to n.
  1490  // It panics if v's Kind is not Slice or if n is negative or
  1491  // greater than the capacity of the slice.
  1492  func (v Value) SetLen(n int) {
  1493  	v.mustBeAssignable()
  1494  	v.mustBe(Slice)
  1495  	s := (*sliceHeader)(v.ptr)
  1496  	if uint(n) > uint(s.Cap) {
  1497  		panic("reflect: slice length out of range in SetLen")
  1498  	}
  1499  	s.Len = n
  1500  }
  1501  
  1502  // SetCap sets v's capacity to n.
  1503  // It panics if v's Kind is not Slice or if n is smaller than the length or
  1504  // greater than the capacity of the slice.
  1505  func (v Value) SetCap(n int) {
  1506  	v.mustBeAssignable()
  1507  	v.mustBe(Slice)
  1508  	s := (*sliceHeader)(v.ptr)
  1509  	if n < s.Len || n > s.Cap {
  1510  		panic("reflect: slice capacity out of range in SetCap")
  1511  	}
  1512  	s.Cap = n
  1513  }
  1514  
  1515  // SetMapIndex sets the value associated with key in the map v to val.
  1516  // It panics if v's Kind is not Map.
  1517  // If val is the zero Value, SetMapIndex deletes the key from the map.
  1518  // Otherwise if v holds a nil map, SetMapIndex will panic.
  1519  // As in Go, key's value must be assignable to the map's key type,
  1520  // and val's value must be assignable to the map's value type.
  1521  func (v Value) SetMapIndex(key, val Value) {
  1522  	v.mustBe(Map)
  1523  	v.mustBeExported()
  1524  	key.mustBeExported()
  1525  	tt := (*mapType)(unsafe.Pointer(v.typ))
  1526  	key = key.assignTo("reflect.Value.SetMapIndex", tt.key, nil)
  1527  	var k unsafe.Pointer
  1528  	if key.flag&flagIndir != 0 {
  1529  		k = key.ptr
  1530  	} else {
  1531  		k = unsafe.Pointer(&key.ptr)
  1532  	}
  1533  	if val.typ == nil {
  1534  		mapdelete(v.typ, v.pointer(), k)
  1535  		return
  1536  	}
  1537  	val.mustBeExported()
  1538  	val = val.assignTo("reflect.Value.SetMapIndex", tt.elem, nil)
  1539  	var e unsafe.Pointer
  1540  	if val.flag&flagIndir != 0 {
  1541  		e = val.ptr
  1542  	} else {
  1543  		e = unsafe.Pointer(&val.ptr)
  1544  	}
  1545  	mapassign(v.typ, v.pointer(), k, e)
  1546  }
  1547  
  1548  // SetUint sets v's underlying value to x.
  1549  // It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64, or if CanSet() is false.
  1550  func (v Value) SetUint(x uint64) {
  1551  	v.mustBeAssignable()
  1552  	switch k := v.kind(); k {
  1553  	default:
  1554  		panic(&ValueError{"reflect.Value.SetUint", v.kind()})
  1555  	case Uint:
  1556  		*(*uint)(v.ptr) = uint(x)
  1557  	case Uint8:
  1558  		*(*uint8)(v.ptr) = uint8(x)
  1559  	case Uint16:
  1560  		*(*uint16)(v.ptr) = uint16(x)
  1561  	case Uint32:
  1562  		*(*uint32)(v.ptr) = uint32(x)
  1563  	case Uint64:
  1564  		*(*uint64)(v.ptr) = x
  1565  	case Uintptr:
  1566  		*(*uintptr)(v.ptr) = uintptr(x)
  1567  	}
  1568  }
  1569  
  1570  // SetPointer sets the unsafe.Pointer value v to x.
  1571  // It panics if v's Kind is not UnsafePointer.
  1572  func (v Value) SetPointer(x unsafe.Pointer) {
  1573  	v.mustBeAssignable()
  1574  	v.mustBe(UnsafePointer)
  1575  	*(*unsafe.Pointer)(v.ptr) = x
  1576  }
  1577  
  1578  // SetString sets v's underlying value to x.
  1579  // It panics if v's Kind is not String or if CanSet() is false.
  1580  func (v Value) SetString(x string) {
  1581  	v.mustBeAssignable()
  1582  	v.mustBe(String)
  1583  	*(*string)(v.ptr) = x
  1584  }
  1585  
  1586  // Slice returns v[i:j].
  1587  // It panics if v's Kind is not Array, Slice or String, or if v is an unaddressable array,
  1588  // or if the indexes are out of bounds.
  1589  func (v Value) Slice(i, j int) Value {
  1590  	var (
  1591  		cap  int
  1592  		typ  *sliceType
  1593  		base unsafe.Pointer
  1594  	)
  1595  	switch kind := v.kind(); kind {
  1596  	default:
  1597  		panic(&ValueError{"reflect.Value.Slice", v.kind()})
  1598  
  1599  	case Array:
  1600  		if v.flag&flagAddr == 0 {
  1601  			panic("reflect.Value.Slice: slice of unaddressable array")
  1602  		}
  1603  		tt := (*arrayType)(unsafe.Pointer(v.typ))
  1604  		cap = int(tt.len)
  1605  		typ = (*sliceType)(unsafe.Pointer(tt.slice))
  1606  		base = v.ptr
  1607  
  1608  	case Slice:
  1609  		typ = (*sliceType)(unsafe.Pointer(v.typ))
  1610  		s := (*sliceHeader)(v.ptr)
  1611  		base = s.Data
  1612  		cap = s.Cap
  1613  
  1614  	case String:
  1615  		s := (*stringHeader)(v.ptr)
  1616  		if i < 0 || j < i || j > s.Len {
  1617  			panic("reflect.Value.Slice: string slice index out of bounds")
  1618  		}
  1619  		var t stringHeader
  1620  		if i < s.Len {
  1621  			t = stringHeader{arrayAt(s.Data, i, 1, "i < s.Len"), j - i}
  1622  		}
  1623  		return Value{v.typ, unsafe.Pointer(&t), v.flag}
  1624  	}
  1625  
  1626  	if i < 0 || j < i || j > cap {
  1627  		panic("reflect.Value.Slice: slice index out of bounds")
  1628  	}
  1629  
  1630  	// Declare slice so that gc can see the base pointer in it.
  1631  	var x []unsafe.Pointer
  1632  
  1633  	// Reinterpret as *sliceHeader to edit.
  1634  	s := (*sliceHeader)(unsafe.Pointer(&x))
  1635  	s.Len = j - i
  1636  	s.Cap = cap - i
  1637  	if cap-i > 0 {
  1638  		s.Data = arrayAt(base, i, typ.elem.Size(), "i < cap")
  1639  	} else {
  1640  		// do not advance pointer, to avoid pointing beyond end of slice
  1641  		s.Data = base
  1642  	}
  1643  
  1644  	fl := v.flag.ro() | flagIndir | flag(Slice)
  1645  	return Value{typ.common(), unsafe.Pointer(&x), fl}
  1646  }
  1647  
  1648  // Slice3 is the 3-index form of the slice operation: it returns v[i:j:k].
  1649  // It panics if v's Kind is not Array or Slice, or if v is an unaddressable array,
  1650  // or if the indexes are out of bounds.
  1651  func (v Value) Slice3(i, j, k int) Value {
  1652  	var (
  1653  		cap  int
  1654  		typ  *sliceType
  1655  		base unsafe.Pointer
  1656  	)
  1657  	switch kind := v.kind(); kind {
  1658  	default:
  1659  		panic(&ValueError{"reflect.Value.Slice3", v.kind()})
  1660  
  1661  	case Array:
  1662  		if v.flag&flagAddr == 0 {
  1663  			panic("reflect.Value.Slice3: slice of unaddressable array")
  1664  		}
  1665  		tt := (*arrayType)(unsafe.Pointer(v.typ))
  1666  		cap = int(tt.len)
  1667  		typ = (*sliceType)(unsafe.Pointer(tt.slice))
  1668  		base = v.ptr
  1669  
  1670  	case Slice:
  1671  		typ = (*sliceType)(unsafe.Pointer(v.typ))
  1672  		s := (*sliceHeader)(v.ptr)
  1673  		base = s.Data
  1674  		cap = s.Cap
  1675  	}
  1676  
  1677  	if i < 0 || j < i || k < j || k > cap {
  1678  		panic("reflect.Value.Slice3: slice index out of bounds")
  1679  	}
  1680  
  1681  	// Declare slice so that the garbage collector
  1682  	// can see the base pointer in it.
  1683  	var x []unsafe.Pointer
  1684  
  1685  	// Reinterpret as *sliceHeader to edit.
  1686  	s := (*sliceHeader)(unsafe.Pointer(&x))
  1687  	s.Len = j - i
  1688  	s.Cap = k - i
  1689  	if k-i > 0 {
  1690  		s.Data = arrayAt(base, i, typ.elem.Size(), "i < k <= cap")
  1691  	} else {
  1692  		// do not advance pointer, to avoid pointing beyond end of slice
  1693  		s.Data = base
  1694  	}
  1695  
  1696  	fl := v.flag.ro() | flagIndir | flag(Slice)
  1697  	return Value{typ.common(), unsafe.Pointer(&x), fl}
  1698  }
  1699  
  1700  // String returns the string v's underlying value, as a string.
  1701  // String is a special case because of Go's String method convention.
  1702  // Unlike the other getters, it does not panic if v's Kind is not String.
  1703  // Instead, it returns a string of the form "<T value>" where T is v's type.
  1704  // The fmt package treats Values specially. It does not call their String
  1705  // method implicitly but instead prints the concrete values they hold.
  1706  func (v Value) String() string {
  1707  	switch k := v.kind(); k {
  1708  	case Invalid:
  1709  		return "<invalid Value>"
  1710  	case String:
  1711  		return *(*string)(v.ptr)
  1712  	}
  1713  	// If you call String on a reflect.Value of other type, it's better to
  1714  	// print something than to panic. Useful in debugging.
  1715  	return "<" + v.Type().String() + " Value>"
  1716  }
  1717  
  1718  // TryRecv attempts to receive a value from the channel v but will not block.
  1719  // It panics if v's Kind is not Chan.
  1720  // If the receive delivers a value, x is the transferred value and ok is true.
  1721  // If the receive cannot finish without blocking, x is the zero Value and ok is false.
  1722  // If the channel is closed, x is the zero value for the channel's element type and ok is false.
  1723  func (v Value) TryRecv() (x Value, ok bool) {
  1724  	v.mustBe(Chan)
  1725  	v.mustBeExported()
  1726  	return v.recv(true)
  1727  }
  1728  
  1729  // TrySend attempts to send x on the channel v but will not block.
  1730  // It panics if v's Kind is not Chan.
  1731  // It reports whether the value was sent.
  1732  // As in Go, x's value must be assignable to the channel's element type.
  1733  func (v Value) TrySend(x Value) bool {
  1734  	v.mustBe(Chan)
  1735  	v.mustBeExported()
  1736  	return v.send(x, true)
  1737  }
  1738  
  1739  // Type returns v's type.
  1740  func (v Value) Type() Type {
  1741  	f := v.flag
  1742  	if f == 0 {
  1743  		panic(&ValueError{"reflect.Value.Type", Invalid})
  1744  	}
  1745  	if f&flagMethod == 0 {
  1746  		// Easy case
  1747  		return v.typ
  1748  	}
  1749  
  1750  	// Method value.
  1751  	// v.typ describes the receiver, not the method type.
  1752  	i := int(v.flag) >> flagMethodShift
  1753  	if v.typ.Kind() == Interface {
  1754  		// Method on interface.
  1755  		tt := (*interfaceType)(unsafe.Pointer(v.typ))
  1756  		if uint(i) >= uint(len(tt.methods)) {
  1757  			panic("reflect: internal error: invalid method index")
  1758  		}
  1759  		m := &tt.methods[i]
  1760  		return v.typ.typeOff(m.typ)
  1761  	}
  1762  	// Method on concrete type.
  1763  	ms := v.typ.exportedMethods()
  1764  	if uint(i) >= uint(len(ms)) {
  1765  		panic("reflect: internal error: invalid method index")
  1766  	}
  1767  	m := ms[i]
  1768  	return v.typ.typeOff(m.mtyp)
  1769  }
  1770  
  1771  // Uint returns v's underlying value, as a uint64.
  1772  // It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.
  1773  func (v Value) Uint() uint64 {
  1774  	k := v.kind()
  1775  	p := v.ptr
  1776  	switch k {
  1777  	case Uint:
  1778  		return uint64(*(*uint)(p))
  1779  	case Uint8:
  1780  		return uint64(*(*uint8)(p))
  1781  	case Uint16:
  1782  		return uint64(*(*uint16)(p))
  1783  	case Uint32:
  1784  		return uint64(*(*uint32)(p))
  1785  	case Uint64:
  1786  		return *(*uint64)(p)
  1787  	case Uintptr:
  1788  		return uint64(*(*uintptr)(p))
  1789  	}
  1790  	panic(&ValueError{"reflect.Value.Uint", v.kind()})
  1791  }
  1792  
  1793  // UnsafeAddr returns a pointer to v's data.
  1794  // It is for advanced clients that also import the "unsafe" package.
  1795  // It panics if v is not addressable.
  1796  func (v Value) UnsafeAddr() uintptr {
  1797  	// TODO: deprecate
  1798  	if v.typ == nil {
  1799  		panic(&ValueError{"reflect.Value.UnsafeAddr", Invalid})
  1800  	}
  1801  	if v.flag&flagAddr == 0 {
  1802  		panic("reflect.Value.UnsafeAddr of unaddressable value")
  1803  	}
  1804  	return uintptr(v.ptr)
  1805  }
  1806  
  1807  // StringHeader is the runtime representation of a string.
  1808  // It cannot be used safely or portably and its representation may
  1809  // change in a later release.
  1810  // Moreover, the Data field is not sufficient to guarantee the data
  1811  // it references will not be garbage collected, so programs must keep
  1812  // a separate, correctly typed pointer to the underlying data.
  1813  type StringHeader struct {
  1814  	Data uintptr
  1815  	Len  int
  1816  }
  1817  
  1818  // stringHeader is a safe version of StringHeader used within this package.
  1819  type stringHeader struct {
  1820  	Data unsafe.Pointer
  1821  	Len  int
  1822  }
  1823  
  1824  // SliceHeader is the runtime representation of a slice.
  1825  // It cannot be used safely or portably and its representation may
  1826  // change in a later release.
  1827  // Moreover, the Data field is not sufficient to guarantee the data
  1828  // it references will not be garbage collected, so programs must keep
  1829  // a separate, correctly typed pointer to the underlying data.
  1830  type SliceHeader struct {
  1831  	Data uintptr
  1832  	Len  int
  1833  	Cap  int
  1834  }
  1835  
  1836  // sliceHeader is a safe version of SliceHeader used within this package.
  1837  type sliceHeader struct {
  1838  	Data unsafe.Pointer
  1839  	Len  int
  1840  	Cap  int
  1841  }
  1842  
  1843  func typesMustMatch(what string, t1, t2 Type) {
  1844  	if t1 != t2 {
  1845  		panic(what + ": " + t1.String() + " != " + t2.String())
  1846  	}
  1847  }
  1848  
  1849  // arrayAt returns the i-th element of p,
  1850  // an array whose elements are eltSize bytes wide.
  1851  // The array pointed at by p must have at least i+1 elements:
  1852  // it is invalid (but impossible to check here) to pass i >= len,
  1853  // because then the result will point outside the array.
  1854  // whySafe must explain why i < len. (Passing "i < len" is fine;
  1855  // the benefit is to surface this assumption at the call site.)
  1856  func arrayAt(p unsafe.Pointer, i int, eltSize uintptr, whySafe string) unsafe.Pointer {
  1857  	return add(p, uintptr(i)*eltSize, "i < len")
  1858  }
  1859  
  1860  // grow grows the slice s so that it can hold extra more values, allocating
  1861  // more capacity if needed. It also returns the old and new slice lengths.
  1862  func grow(s Value, extra int) (Value, int, int) {
  1863  	i0 := s.Len()
  1864  	i1 := i0 + extra
  1865  	if i1 < i0 {
  1866  		panic("reflect.Append: slice overflow")
  1867  	}
  1868  	m := s.Cap()
  1869  	if i1 <= m {
  1870  		return s.Slice(0, i1), i0, i1
  1871  	}
  1872  	if m == 0 {
  1873  		m = extra
  1874  	} else {
  1875  		for m < i1 {
  1876  			if i0 < 1024 {
  1877  				m += m
  1878  			} else {
  1879  				m += m / 4
  1880  			}
  1881  		}
  1882  	}
  1883  	t := MakeSlice(s.Type(), i1, m)
  1884  	Copy(t, s)
  1885  	return t, i0, i1
  1886  }
  1887  
  1888  // Append appends the values x to a slice s and returns the resulting slice.
  1889  // As in Go, each x's value must be assignable to the slice's element type.
  1890  func Append(s Value, x ...Value) Value {
  1891  	s.mustBe(Slice)
  1892  	s, i0, i1 := grow(s, len(x))
  1893  	for i, j := i0, 0; i < i1; i, j = i+1, j+1 {
  1894  		s.Index(i).Set(x[j])
  1895  	}
  1896  	return s
  1897  }
  1898  
  1899  // AppendSlice appends a slice t to a slice s and returns the resulting slice.
  1900  // The slices s and t must have the same element type.
  1901  func AppendSlice(s, t Value) Value {
  1902  	s.mustBe(Slice)
  1903  	t.mustBe(Slice)
  1904  	typesMustMatch("reflect.AppendSlice", s.Type().Elem(), t.Type().Elem())
  1905  	s, i0, i1 := grow(s, t.Len())
  1906  	Copy(s.Slice(i0, i1), t)
  1907  	return s
  1908  }
  1909  
  1910  // Copy copies the contents of src into dst until either
  1911  // dst has been filled or src has been exhausted.
  1912  // It returns the number of elements copied.
  1913  // Dst and src each must have kind Slice or Array, and
  1914  // dst and src must have the same element type.
  1915  //
  1916  // As a special case, src can have kind String if the element type of dst is kind Uint8.
  1917  func Copy(dst, src Value) int {
  1918  	dk := dst.kind()
  1919  	if dk != Array && dk != Slice {
  1920  		panic(&ValueError{"reflect.Copy", dk})
  1921  	}
  1922  	if dk == Array {
  1923  		dst.mustBeAssignable()
  1924  	}
  1925  	dst.mustBeExported()
  1926  
  1927  	sk := src.kind()
  1928  	var stringCopy bool
  1929  	if sk != Array && sk != Slice {
  1930  		stringCopy = sk == String && dst.typ.Elem().Kind() == Uint8
  1931  		if !stringCopy {
  1932  			panic(&ValueError{"reflect.Copy", sk})
  1933  		}
  1934  	}
  1935  	src.mustBeExported()
  1936  
  1937  	de := dst.typ.Elem()
  1938  	if !stringCopy {
  1939  		se := src.typ.Elem()
  1940  		typesMustMatch("reflect.Copy", de, se)
  1941  	}
  1942  
  1943  	var ds, ss sliceHeader
  1944  	if dk == Array {
  1945  		ds.Data = dst.ptr
  1946  		ds.Len = dst.Len()
  1947  		ds.Cap = ds.Len
  1948  	} else {
  1949  		ds = *(*sliceHeader)(dst.ptr)
  1950  	}
  1951  	if sk == Array {
  1952  		ss.Data = src.ptr
  1953  		ss.Len = src.Len()
  1954  		ss.Cap = ss.Len
  1955  	} else if sk == Slice {
  1956  		ss = *(*sliceHeader)(src.ptr)
  1957  	} else {
  1958  		sh := *(*stringHeader)(src.ptr)
  1959  		ss.Data = sh.Data
  1960  		ss.Len = sh.Len
  1961  		ss.Cap = sh.Len
  1962  	}
  1963  
  1964  	return typedslicecopy(de.common(), ds, ss)
  1965  }
  1966  
  1967  // A runtimeSelect is a single case passed to rselect.
  1968  // This must match ../runtime/select.go:/runtimeSelect
  1969  type runtimeSelect struct {
  1970  	dir SelectDir      // SelectSend, SelectRecv or SelectDefault
  1971  	typ *rtype         // channel type
  1972  	ch  unsafe.Pointer // channel
  1973  	val unsafe.Pointer // ptr to data (SendDir) or ptr to receive buffer (RecvDir)
  1974  }
  1975  
  1976  // rselect runs a select. It returns the index of the chosen case.
  1977  // If the case was a receive, val is filled in with the received value.
  1978  // The conventional OK bool indicates whether the receive corresponds
  1979  // to a sent value.
  1980  //go:noescape
  1981  func rselect([]runtimeSelect) (chosen int, recvOK bool)
  1982  
  1983  // A SelectDir describes the communication direction of a select case.
  1984  type SelectDir int
  1985  
  1986  // NOTE: These values must match ../runtime/select.go:/selectDir.
  1987  
  1988  const (
  1989  	_             SelectDir = iota
  1990  	SelectSend              // case Chan <- Send
  1991  	SelectRecv              // case <-Chan:
  1992  	SelectDefault           // default
  1993  )
  1994  
  1995  // A SelectCase describes a single case in a select operation.
  1996  // The kind of case depends on Dir, the communication direction.
  1997  //
  1998  // If Dir is SelectDefault, the case represents a default case.
  1999  // Chan and Send must be zero Values.
  2000  //
  2001  // If Dir is SelectSend, the case represents a send operation.
  2002  // Normally Chan's underlying value must be a channel, and Send's underlying value must be
  2003  // assignable to the channel's element type. As a special case, if Chan is a zero Value,
  2004  // then the case is ignored, and the field Send will also be ignored and may be either zero
  2005  // or non-zero.
  2006  //
  2007  // If Dir is SelectRecv, the case represents a receive operation.
  2008  // Normally Chan's underlying value must be a channel and Send must be a zero Value.
  2009  // If Chan is a zero Value, then the case is ignored, but Send must still be a zero Value.
  2010  // When a receive operation is selected, the received Value is returned by Select.
  2011  //
  2012  type SelectCase struct {
  2013  	Dir  SelectDir // direction of case
  2014  	Chan Value     // channel to use (for send or receive)
  2015  	Send Value     // value to send (for send)
  2016  }
  2017  
  2018  // Select executes a select operation described by the list of cases.
  2019  // Like the Go select statement, it blocks until at least one of the cases
  2020  // can proceed, makes a uniform pseudo-random choice,
  2021  // and then executes that case. It returns the index of the chosen case
  2022  // and, if that case was a receive operation, the value received and a
  2023  // boolean indicating whether the value corresponds to a send on the channel
  2024  // (as opposed to a zero value received because the channel is closed).
  2025  func Select(cases []SelectCase) (chosen int, recv Value, recvOK bool) {
  2026  	// NOTE: Do not trust that caller is not modifying cases data underfoot.
  2027  	// The range is safe because the caller cannot modify our copy of the len
  2028  	// and each iteration makes its own copy of the value c.
  2029  	runcases := make([]runtimeSelect, len(cases))
  2030  	haveDefault := false
  2031  	for i, c := range cases {
  2032  		rc := &runcases[i]
  2033  		rc.dir = c.Dir
  2034  		switch c.Dir {
  2035  		default:
  2036  			panic("reflect.Select: invalid Dir")
  2037  
  2038  		case SelectDefault: // default
  2039  			if haveDefault {
  2040  				panic("reflect.Select: multiple default cases")
  2041  			}
  2042  			haveDefault = true
  2043  			if c.Chan.IsValid() {
  2044  				panic("reflect.Select: default case has Chan value")
  2045  			}
  2046  			if c.Send.IsValid() {
  2047  				panic("reflect.Select: default case has Send value")
  2048  			}
  2049  
  2050  		case SelectSend:
  2051  			ch := c.Chan
  2052  			if !ch.IsValid() {
  2053  				break
  2054  			}
  2055  			ch.mustBe(Chan)
  2056  			ch.mustBeExported()
  2057  			tt := (*chanType)(unsafe.Pointer(ch.typ))
  2058  			if ChanDir(tt.dir)&SendDir == 0 {
  2059  				panic("reflect.Select: SendDir case using recv-only channel")
  2060  			}
  2061  			rc.ch = ch.pointer()
  2062  			rc.typ = &tt.rtype
  2063  			v := c.Send
  2064  			if !v.IsValid() {
  2065  				panic("reflect.Select: SendDir case missing Send value")
  2066  			}
  2067  			v.mustBeExported()
  2068  			v = v.assignTo("reflect.Select", tt.elem, nil)
  2069  			if v.flag&flagIndir != 0 {
  2070  				rc.val = v.ptr
  2071  			} else {
  2072  				rc.val = unsafe.Pointer(&v.ptr)
  2073  			}
  2074  
  2075  		case SelectRecv:
  2076  			if c.Send.IsValid() {
  2077  				panic("reflect.Select: RecvDir case has Send value")
  2078  			}
  2079  			ch := c.Chan
  2080  			if !ch.IsValid() {
  2081  				break
  2082  			}
  2083  			ch.mustBe(Chan)
  2084  			ch.mustBeExported()
  2085  			tt := (*chanType)(unsafe.Pointer(ch.typ))
  2086  			if ChanDir(tt.dir)&RecvDir == 0 {
  2087  				panic("reflect.Select: RecvDir case using send-only channel")
  2088  			}
  2089  			rc.ch = ch.pointer()
  2090  			rc.typ = &tt.rtype
  2091  			rc.val = unsafe_New(tt.elem)
  2092  		}
  2093  	}
  2094  
  2095  	chosen, recvOK = rselect(runcases)
  2096  	if runcases[chosen].dir == SelectRecv {
  2097  		tt := (*chanType)(unsafe.Pointer(runcases[chosen].typ))
  2098  		t := tt.elem
  2099  		p := runcases[chosen].val
  2100  		fl := flag(t.Kind())
  2101  		if ifaceIndir(t) {
  2102  			recv = Value{t, p, fl | flagIndir}
  2103  		} else {
  2104  			recv = Value{t, *(*unsafe.Pointer)(p), fl}
  2105  		}
  2106  	}
  2107  	return chosen, recv, recvOK
  2108  }
  2109  
  2110  /*
  2111   * constructors
  2112   */
  2113  
  2114  // implemented in package runtime
  2115  func unsafe_New(*rtype) unsafe.Pointer
  2116  func unsafe_NewArray(*rtype, int) unsafe.Pointer
  2117  
  2118  // MakeSlice creates a new zero-initialized slice value
  2119  // for the specified slice type, length, and capacity.
  2120  func MakeSlice(typ Type, len, cap int) Value {
  2121  	if typ.Kind() != Slice {
  2122  		panic("reflect.MakeSlice of non-slice type")
  2123  	}
  2124  	if len < 0 {
  2125  		panic("reflect.MakeSlice: negative len")
  2126  	}
  2127  	if cap < 0 {
  2128  		panic("reflect.MakeSlice: negative cap")
  2129  	}
  2130  	if len > cap {
  2131  		panic("reflect.MakeSlice: len > cap")
  2132  	}
  2133  
  2134  	s := sliceHeader{unsafe_NewArray(typ.Elem().(*rtype), cap), len, cap}
  2135  	return Value{typ.(*rtype), unsafe.Pointer(&s), flagIndir | flag(Slice)}
  2136  }
  2137  
  2138  // MakeChan creates a new channel with the specified type and buffer size.
  2139  func MakeChan(typ Type, buffer int) Value {
  2140  	if typ.Kind() != Chan {
  2141  		panic("reflect.MakeChan of non-chan type")
  2142  	}
  2143  	if buffer < 0 {
  2144  		panic("reflect.MakeChan: negative buffer size")
  2145  	}
  2146  	if typ.ChanDir() != BothDir {
  2147  		panic("reflect.MakeChan: unidirectional channel type")
  2148  	}
  2149  	t := typ.(*rtype)
  2150  	ch := makechan(t, buffer)
  2151  	return Value{t, ch, flag(Chan)}
  2152  }
  2153  
  2154  // MakeMap creates a new map with the specified type.
  2155  func MakeMap(typ Type) Value {
  2156  	return MakeMapWithSize(typ, 0)
  2157  }
  2158  
  2159  // MakeMapWithSize creates a new map with the specified type
  2160  // and initial space for approximately n elements.
  2161  func MakeMapWithSize(typ Type, n int) Value {
  2162  	if typ.Kind() != Map {
  2163  		panic("reflect.MakeMapWithSize of non-map type")
  2164  	}
  2165  	t := typ.(*rtype)
  2166  	m := makemap(t, n)
  2167  	return Value{t, m, flag(Map)}
  2168  }
  2169  
  2170  // Indirect returns the value that v points to.
  2171  // If v is a nil pointer, Indirect returns a zero Value.
  2172  // If v is not a pointer, Indirect returns v.
  2173  func Indirect(v Value) Value {
  2174  	if v.Kind() != Ptr {
  2175  		return v
  2176  	}
  2177  	return v.Elem()
  2178  }
  2179  
  2180  // ValueOf returns a new Value initialized to the concrete value
  2181  // stored in the interface i. ValueOf(nil) returns the zero Value.
  2182  func ValueOf(i interface{}) Value {
  2183  	if i == nil {
  2184  		return Value{}
  2185  	}
  2186  
  2187  	// TODO: Maybe allow contents of a Value to live on the stack.
  2188  	// For now we make the contents always escape to the heap. It
  2189  	// makes life easier in a few places (see chanrecv/mapassign
  2190  	// comment below).
  2191  	escapes(i)
  2192  
  2193  	return unpackEface(i)
  2194  }
  2195  
  2196  // Zero returns a Value representing the zero value for the specified type.
  2197  // The result is different from the zero value of the Value struct,
  2198  // which represents no value at all.
  2199  // For example, Zero(TypeOf(42)) returns a Value with Kind Int and value 0.
  2200  // The returned value is neither addressable nor settable.
  2201  func Zero(typ Type) Value {
  2202  	if typ == nil {
  2203  		panic("reflect: Zero(nil)")
  2204  	}
  2205  	t := typ.(*rtype)
  2206  	fl := flag(t.Kind())
  2207  	if ifaceIndir(t) {
  2208  		return Value{t, unsafe_New(t), fl | flagIndir}
  2209  	}
  2210  	return Value{t, nil, fl}
  2211  }
  2212  
  2213  // New returns a Value representing a pointer to a new zero value
  2214  // for the specified type. That is, the returned Value's Type is PtrTo(typ).
  2215  func New(typ Type) Value {
  2216  	if typ == nil {
  2217  		panic("reflect: New(nil)")
  2218  	}
  2219  	t := typ.(*rtype)
  2220  	ptr := unsafe_New(t)
  2221  	fl := flag(Ptr)
  2222  	return Value{t.ptrTo(), ptr, fl}
  2223  }
  2224  
  2225  // NewAt returns a Value representing a pointer to a value of the
  2226  // specified type, using p as that pointer.
  2227  func NewAt(typ Type, p unsafe.Pointer) Value {
  2228  	fl := flag(Ptr)
  2229  	t := typ.(*rtype)
  2230  	return Value{t.ptrTo(), p, fl}
  2231  }
  2232  
  2233  // assignTo returns a value v that can be assigned directly to typ.
  2234  // It panics if v is not assignable to typ.
  2235  // For a conversion to an interface type, target is a suggested scratch space to use.
  2236  func (v Value) assignTo(context string, dst *rtype, target unsafe.Pointer) Value {
  2237  	if v.flag&flagMethod != 0 {
  2238  		v = makeMethodValue(context, v)
  2239  	}
  2240  
  2241  	switch {
  2242  	case directlyAssignable(dst, v.typ):
  2243  		// Overwrite type so that they match.
  2244  		// Same memory layout, so no harm done.
  2245  		fl := v.flag&(flagAddr|flagIndir) | v.flag.ro()
  2246  		fl |= flag(dst.Kind())
  2247  		return Value{dst, v.ptr, fl}
  2248  
  2249  	case implements(dst, v.typ):
  2250  		if target == nil {
  2251  			target = unsafe_New(dst)
  2252  		}
  2253  		if v.Kind() == Interface && v.IsNil() {
  2254  			// A nil ReadWriter passed to nil Reader is OK,
  2255  			// but using ifaceE2I below will panic.
  2256  			// Avoid the panic by returning a nil dst (e.g., Reader) explicitly.
  2257  			return Value{dst, nil, flag(Interface)}
  2258  		}
  2259  		x := valueInterface(v, false)
  2260  		if dst.NumMethod() == 0 {
  2261  			*(*interface{})(target) = x
  2262  		} else {
  2263  			ifaceE2I(dst, x, target)
  2264  		}
  2265  		return Value{dst, target, flagIndir | flag(Interface)}
  2266  	}
  2267  
  2268  	// Failed.
  2269  	panic(context + ": value of type " + v.typ.String() + " is not assignable to type " + dst.String())
  2270  }
  2271  
  2272  // Convert returns the value v converted to type t.
  2273  // If the usual Go conversion rules do not allow conversion
  2274  // of the value v to type t, Convert panics.
  2275  func (v Value) Convert(t Type) Value {
  2276  	if v.flag&flagMethod != 0 {
  2277  		v = makeMethodValue("Convert", v)
  2278  	}
  2279  	op := convertOp(t.common(), v.typ)
  2280  	if op == nil {
  2281  		panic("reflect.Value.Convert: value of type " + v.typ.String() + " cannot be converted to type " + t.String())
  2282  	}
  2283  	return op(v, t)
  2284  }
  2285  
  2286  // convertOp returns the function to convert a value of type src
  2287  // to a value of type dst. If the conversion is illegal, convertOp returns nil.
  2288  func convertOp(dst, src *rtype) func(Value, Type) Value {
  2289  	switch src.Kind() {
  2290  	case Int, Int8, Int16, Int32, Int64:
  2291  		switch dst.Kind() {
  2292  		case Int, Int8, Int16, Int32, Int64, Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
  2293  			return cvtInt
  2294  		case Float32, Float64:
  2295  			return cvtIntFloat
  2296  		case String:
  2297  			return cvtIntString
  2298  		}
  2299  
  2300  	case Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
  2301  		switch dst.Kind() {
  2302  		case Int, Int8, Int16, Int32, Int64, Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
  2303  			return cvtUint
  2304  		case Float32, Float64:
  2305  			return cvtUintFloat
  2306  		case String:
  2307  			return cvtUintString
  2308  		}
  2309  
  2310  	case Float32, Float64:
  2311  		switch dst.Kind() {
  2312  		case Int, Int8, Int16, Int32, Int64:
  2313  			return cvtFloatInt
  2314  		case Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
  2315  			return cvtFloatUint
  2316  		case Float32, Float64:
  2317  			return cvtFloat
  2318  		}
  2319  
  2320  	case Complex64, Complex128:
  2321  		switch dst.Kind() {
  2322  		case Complex64, Complex128:
  2323  			return cvtComplex
  2324  		}
  2325  
  2326  	case String:
  2327  		if dst.Kind() == Slice && dst.Elem().PkgPath() == "" {
  2328  			switch dst.Elem().Kind() {
  2329  			case Uint8:
  2330  				return cvtStringBytes
  2331  			case Int32:
  2332  				return cvtStringRunes
  2333  			}
  2334  		}
  2335  
  2336  	case Slice:
  2337  		if dst.Kind() == String && src.Elem().PkgPath() == "" {
  2338  			switch src.Elem().Kind() {
  2339  			case Uint8:
  2340  				return cvtBytesString
  2341  			case Int32:
  2342  				return cvtRunesString
  2343  			}
  2344  		}
  2345  	}
  2346  
  2347  	// dst and src have same underlying type.
  2348  	if haveIdenticalUnderlyingType(dst, src, false) {
  2349  		return cvtDirect
  2350  	}
  2351  
  2352  	// dst and src are non-defined pointer types with same underlying base type.
  2353  	if dst.Kind() == Ptr && dst.Name() == "" &&
  2354  		src.Kind() == Ptr && src.Name() == "" &&
  2355  		haveIdenticalUnderlyingType(dst.Elem().common(), src.Elem().common(), false) {
  2356  		return cvtDirect
  2357  	}
  2358  
  2359  	if implements(dst, src) {
  2360  		if src.Kind() == Interface {
  2361  			return cvtI2I
  2362  		}
  2363  		return cvtT2I
  2364  	}
  2365  
  2366  	return nil
  2367  }
  2368  
  2369  // makeInt returns a Value of type t equal to bits (possibly truncated),
  2370  // where t is a signed or unsigned int type.
  2371  func makeInt(f flag, bits uint64, t Type) Value {
  2372  	typ := t.common()
  2373  	ptr := unsafe_New(typ)
  2374  	switch typ.size {
  2375  	case 1:
  2376  		*(*uint8)(ptr) = uint8(bits)
  2377  	case 2:
  2378  		*(*uint16)(ptr) = uint16(bits)
  2379  	case 4:
  2380  		*(*uint32)(ptr) = uint32(bits)
  2381  	case 8:
  2382  		*(*uint64)(ptr) = bits
  2383  	}
  2384  	return Value{typ, ptr, f | flagIndir | flag(typ.Kind())}
  2385  }
  2386  
  2387  // makeFloat returns a Value of type t equal to v (possibly truncated to float32),
  2388  // where t is a float32 or float64 type.
  2389  func makeFloat(f flag, v float64, t Type) Value {
  2390  	typ := t.common()
  2391  	ptr := unsafe_New(typ)
  2392  	switch typ.size {
  2393  	case 4:
  2394  		*(*float32)(ptr) = float32(v)
  2395  	case 8:
  2396  		*(*float64)(ptr) = v
  2397  	}
  2398  	return Value{typ, ptr, f | flagIndir | flag(typ.Kind())}
  2399  }
  2400  
  2401  // makeComplex returns a Value of type t equal to v (possibly truncated to complex64),
  2402  // where t is a complex64 or complex128 type.
  2403  func makeComplex(f flag, v complex128, t Type) Value {
  2404  	typ := t.common()
  2405  	ptr := unsafe_New(typ)
  2406  	switch typ.size {
  2407  	case 8:
  2408  		*(*complex64)(ptr) = complex64(v)
  2409  	case 16:
  2410  		*(*complex128)(ptr) = v
  2411  	}
  2412  	return Value{typ, ptr, f | flagIndir | flag(typ.Kind())}
  2413  }
  2414  
  2415  func makeString(f flag, v string, t Type) Value {
  2416  	ret := New(t).Elem()
  2417  	ret.SetString(v)
  2418  	ret.flag = ret.flag&^flagAddr | f
  2419  	return ret
  2420  }
  2421  
  2422  func makeBytes(f flag, v []byte, t Type) Value {
  2423  	ret := New(t).Elem()
  2424  	ret.SetBytes(v)
  2425  	ret.flag = ret.flag&^flagAddr | f
  2426  	return ret
  2427  }
  2428  
  2429  func makeRunes(f flag, v []rune, t Type) Value {
  2430  	ret := New(t).Elem()
  2431  	ret.setRunes(v)
  2432  	ret.flag = ret.flag&^flagAddr | f
  2433  	return ret
  2434  }
  2435  
  2436  // These conversion functions are returned by convertOp
  2437  // for classes of conversions. For example, the first function, cvtInt,
  2438  // takes any value v of signed int type and returns the value converted
  2439  // to type t, where t is any signed or unsigned int type.
  2440  
  2441  // convertOp: intXX -> [u]intXX
  2442  func cvtInt(v Value, t Type) Value {
  2443  	return makeInt(v.flag.ro(), uint64(v.Int()), t)
  2444  }
  2445  
  2446  // convertOp: uintXX -> [u]intXX
  2447  func cvtUint(v Value, t Type) Value {
  2448  	return makeInt(v.flag.ro(), v.Uint(), t)
  2449  }
  2450  
  2451  // convertOp: floatXX -> intXX
  2452  func cvtFloatInt(v Value, t Type) Value {
  2453  	return makeInt(v.flag.ro(), uint64(int64(v.Float())), t)
  2454  }
  2455  
  2456  // convertOp: floatXX -> uintXX
  2457  func cvtFloatUint(v Value, t Type) Value {
  2458  	return makeInt(v.flag.ro(), uint64(v.Float()), t)
  2459  }
  2460  
  2461  // convertOp: intXX -> floatXX
  2462  func cvtIntFloat(v Value, t Type) Value {
  2463  	return makeFloat(v.flag.ro(), float64(v.Int()), t)
  2464  }
  2465  
  2466  // convertOp: uintXX -> floatXX
  2467  func cvtUintFloat(v Value, t Type) Value {
  2468  	return makeFloat(v.flag.ro(), float64(v.Uint()), t)
  2469  }
  2470  
  2471  // convertOp: floatXX -> floatXX
  2472  func cvtFloat(v Value, t Type) Value {
  2473  	return makeFloat(v.flag.ro(), v.Float(), t)
  2474  }
  2475  
  2476  // convertOp: complexXX -> complexXX
  2477  func cvtComplex(v Value, t Type) Value {
  2478  	return makeComplex(v.flag.ro(), v.Complex(), t)
  2479  }
  2480  
  2481  // convertOp: intXX -> string
  2482  func cvtIntString(v Value, t Type) Value {
  2483  	return makeString(v.flag.ro(), string(v.Int()), t)
  2484  }
  2485  
  2486  // convertOp: uintXX -> string
  2487  func cvtUintString(v Value, t Type) Value {
  2488  	return makeString(v.flag.ro(), string(v.Uint()), t)
  2489  }
  2490  
  2491  // convertOp: []byte -> string
  2492  func cvtBytesString(v Value, t Type) Value {
  2493  	return makeString(v.flag.ro(), string(v.Bytes()), t)
  2494  }
  2495  
  2496  // convertOp: string -> []byte
  2497  func cvtStringBytes(v Value, t Type) Value {
  2498  	return makeBytes(v.flag.ro(), []byte(v.String()), t)
  2499  }
  2500  
  2501  // convertOp: []rune -> string
  2502  func cvtRunesString(v Value, t Type) Value {
  2503  	return makeString(v.flag.ro(), string(v.runes()), t)
  2504  }
  2505  
  2506  // convertOp: string -> []rune
  2507  func cvtStringRunes(v Value, t Type) Value {
  2508  	return makeRunes(v.flag.ro(), []rune(v.String()), t)
  2509  }
  2510  
  2511  // convertOp: direct copy
  2512  func cvtDirect(v Value, typ Type) Value {
  2513  	f := v.flag
  2514  	t := typ.common()
  2515  	ptr := v.ptr
  2516  	if f&flagAddr != 0 {
  2517  		// indirect, mutable word - make a copy
  2518  		c := unsafe_New(t)
  2519  		typedmemmove(t, c, ptr)
  2520  		ptr = c
  2521  		f &^= flagAddr
  2522  	}
  2523  	return Value{t, ptr, v.flag.ro() | f} // v.flag.ro()|f == f?
  2524  }
  2525  
  2526  // convertOp: concrete -> interface
  2527  func cvtT2I(v Value, typ Type) Value {
  2528  	target := unsafe_New(typ.common())
  2529  	x := valueInterface(v, false)
  2530  	if typ.NumMethod() == 0 {
  2531  		*(*interface{})(target) = x
  2532  	} else {
  2533  		ifaceE2I(typ.(*rtype), x, target)
  2534  	}
  2535  	return Value{typ.common(), target, v.flag.ro() | flagIndir | flag(Interface)}
  2536  }
  2537  
  2538  // convertOp: interface -> interface
  2539  func cvtI2I(v Value, typ Type) Value {
  2540  	if v.IsNil() {
  2541  		ret := Zero(typ)
  2542  		ret.flag |= v.flag.ro()
  2543  		return ret
  2544  	}
  2545  	return cvtT2I(v.Elem(), typ)
  2546  }
  2547  
  2548  // implemented in ../runtime
  2549  func chancap(ch unsafe.Pointer) int
  2550  func chanclose(ch unsafe.Pointer)
  2551  func chanlen(ch unsafe.Pointer) int
  2552  
  2553  // Note: some of the noescape annotations below are technically a lie,
  2554  // but safe in the context of this package. Functions like chansend
  2555  // and mapassign don't escape the referent, but may escape anything
  2556  // the referent points to (they do shallow copies of the referent).
  2557  // It is safe in this package because the referent may only point
  2558  // to something a Value may point to, and that is always in the heap
  2559  // (due to the escapes() call in ValueOf).
  2560  
  2561  //go:noescape
  2562  func chanrecv(ch unsafe.Pointer, nb bool, val unsafe.Pointer) (selected, received bool)
  2563  
  2564  //go:noescape
  2565  func chansend(ch unsafe.Pointer, val unsafe.Pointer, nb bool) bool
  2566  
  2567  func makechan(typ *rtype, size int) (ch unsafe.Pointer)
  2568  func makemap(t *rtype, cap int) (m unsafe.Pointer)
  2569  
  2570  //go:noescape
  2571  func mapaccess(t *rtype, m unsafe.Pointer, key unsafe.Pointer) (val unsafe.Pointer)
  2572  
  2573  //go:noescape
  2574  func mapassign(t *rtype, m unsafe.Pointer, key, val unsafe.Pointer)
  2575  
  2576  //go:noescape
  2577  func mapdelete(t *rtype, m unsafe.Pointer, key unsafe.Pointer)
  2578  
  2579  // m escapes into the return value, but the caller of mapiterinit
  2580  // doesn't let the return value escape.
  2581  //go:noescape
  2582  func mapiterinit(t *rtype, m unsafe.Pointer) unsafe.Pointer
  2583  
  2584  //go:noescape
  2585  func mapiterkey(it unsafe.Pointer) (key unsafe.Pointer)
  2586  
  2587  //go:noescape
  2588  func mapiternext(it unsafe.Pointer)
  2589  
  2590  //go:noescape
  2591  func maplen(m unsafe.Pointer) int
  2592  
  2593  // call calls fn with a copy of the n argument bytes pointed at by arg.
  2594  // After fn returns, reflectcall copies n-retoffset result bytes
  2595  // back into arg+retoffset before returning. If copying result bytes back,
  2596  // the caller must pass the argument frame type as argtype, so that
  2597  // call can execute appropriate write barriers during the copy.
  2598  func call(argtype *rtype, fn, arg unsafe.Pointer, n uint32, retoffset uint32)
  2599  
  2600  func ifaceE2I(t *rtype, src interface{}, dst unsafe.Pointer)
  2601  
  2602  // memmove copies size bytes to dst from src. No write barriers are used.
  2603  //go:noescape
  2604  func memmove(dst, src unsafe.Pointer, size uintptr)
  2605  
  2606  // typedmemmove copies a value of type t to dst from src.
  2607  //go:noescape
  2608  func typedmemmove(t *rtype, dst, src unsafe.Pointer)
  2609  
  2610  // typedmemmovepartial is like typedmemmove but assumes that
  2611  // dst and src point off bytes into the value and only copies size bytes.
  2612  //go:noescape
  2613  func typedmemmovepartial(t *rtype, dst, src unsafe.Pointer, off, size uintptr)
  2614  
  2615  // typedmemclr zeros the value at ptr of type t.
  2616  //go:noescape
  2617  func typedmemclr(t *rtype, ptr unsafe.Pointer)
  2618  
  2619  // typedmemclrpartial is like typedmemclr but assumes that
  2620  // dst points off bytes into the value and only clears size bytes.
  2621  //go:noescape
  2622  func typedmemclrpartial(t *rtype, ptr unsafe.Pointer, off, size uintptr)
  2623  
  2624  // typedslicecopy copies a slice of elemType values from src to dst,
  2625  // returning the number of elements copied.
  2626  //go:noescape
  2627  func typedslicecopy(elemType *rtype, dst, src sliceHeader) int
  2628  
  2629  // Dummy annotation marking that the value x escapes,
  2630  // for use in cases where the reflect code is so clever that
  2631  // the compiler cannot follow.
  2632  func escapes(x interface{}) {
  2633  	if dummy.b {
  2634  		dummy.x = x
  2635  	}
  2636  }
  2637  
  2638  var dummy struct {
  2639  	b bool
  2640  	x interface{}
  2641  }
  2642  

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