...
Run Format

Source file src/fmt/print.go

Documentation: fmt

     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 fmt
     6  
     7  import (
     8  	"errors"
     9  	"internal/fmtsort"
    10  	"io"
    11  	"os"
    12  	"reflect"
    13  	"sync"
    14  	"unicode/utf8"
    15  )
    16  
    17  // Strings for use with buffer.WriteString.
    18  // This is less overhead than using buffer.Write with byte arrays.
    19  const (
    20  	commaSpaceString  = ", "
    21  	nilAngleString    = "<nil>"
    22  	nilParenString    = "(nil)"
    23  	nilString         = "nil"
    24  	mapString         = "map["
    25  	percentBangString = "%!"
    26  	missingString     = "(MISSING)"
    27  	badIndexString    = "(BADINDEX)"
    28  	panicString       = "(PANIC="
    29  	extraString       = "%!(EXTRA "
    30  	badWidthString    = "%!(BADWIDTH)"
    31  	badPrecString     = "%!(BADPREC)"
    32  	noVerbString      = "%!(NOVERB)"
    33  	invReflectString  = "<invalid reflect.Value>"
    34  )
    35  
    36  // State represents the printer state passed to custom formatters.
    37  // It provides access to the io.Writer interface plus information about
    38  // the flags and options for the operand's format specifier.
    39  type State interface {
    40  	// Write is the function to call to emit formatted output to be printed.
    41  	Write(b []byte) (n int, err error)
    42  	// Width returns the value of the width option and whether it has been set.
    43  	Width() (wid int, ok bool)
    44  	// Precision returns the value of the precision option and whether it has been set.
    45  	Precision() (prec int, ok bool)
    46  
    47  	// Flag reports whether the flag c, a character, has been set.
    48  	Flag(c int) bool
    49  }
    50  
    51  // Formatter is the interface implemented by values with a custom formatter.
    52  // The implementation of Format may call Sprint(f) or Fprint(f) etc.
    53  // to generate its output.
    54  type Formatter interface {
    55  	Format(f State, c rune)
    56  }
    57  
    58  // Stringer is implemented by any value that has a String method,
    59  // which defines the ``native'' format for that value.
    60  // The String method is used to print values passed as an operand
    61  // to any format that accepts a string or to an unformatted printer
    62  // such as Print.
    63  type Stringer interface {
    64  	String() string
    65  }
    66  
    67  // GoStringer is implemented by any value that has a GoString method,
    68  // which defines the Go syntax for that value.
    69  // The GoString method is used to print values passed as an operand
    70  // to a %#v format.
    71  type GoStringer interface {
    72  	GoString() string
    73  }
    74  
    75  // Use simple []byte instead of bytes.Buffer to avoid large dependency.
    76  type buffer []byte
    77  
    78  func (b *buffer) Write(p []byte) {
    79  	*b = append(*b, p...)
    80  }
    81  
    82  func (b *buffer) WriteString(s string) {
    83  	*b = append(*b, s...)
    84  }
    85  
    86  func (b *buffer) WriteByte(c byte) {
    87  	*b = append(*b, c)
    88  }
    89  
    90  func (bp *buffer) WriteRune(r rune) {
    91  	if r < utf8.RuneSelf {
    92  		*bp = append(*bp, byte(r))
    93  		return
    94  	}
    95  
    96  	b := *bp
    97  	n := len(b)
    98  	for n+utf8.UTFMax > cap(b) {
    99  		b = append(b, 0)
   100  	}
   101  	w := utf8.EncodeRune(b[n:n+utf8.UTFMax], r)
   102  	*bp = b[:n+w]
   103  }
   104  
   105  // pp is used to store a printer's state and is reused with sync.Pool to avoid allocations.
   106  type pp struct {
   107  	buf buffer
   108  
   109  	// arg holds the current item, as an interface{}.
   110  	arg interface{}
   111  
   112  	// value is used instead of arg for reflect values.
   113  	value reflect.Value
   114  
   115  	// fmt is used to format basic items such as integers or strings.
   116  	fmt fmt
   117  
   118  	// reordered records whether the format string used argument reordering.
   119  	reordered bool
   120  	// goodArgNum records whether the most recent reordering directive was valid.
   121  	goodArgNum bool
   122  	// panicking is set by catchPanic to avoid infinite panic, recover, panic, ... recursion.
   123  	panicking bool
   124  	// erroring is set when printing an error string to guard against calling handleMethods.
   125  	erroring bool
   126  }
   127  
   128  var ppFree = sync.Pool{
   129  	New: func() interface{} { return new(pp) },
   130  }
   131  
   132  // newPrinter allocates a new pp struct or grabs a cached one.
   133  func newPrinter() *pp {
   134  	p := ppFree.Get().(*pp)
   135  	p.panicking = false
   136  	p.erroring = false
   137  	p.fmt.init(&p.buf)
   138  	return p
   139  }
   140  
   141  // free saves used pp structs in ppFree; avoids an allocation per invocation.
   142  func (p *pp) free() {
   143  	// Proper usage of a sync.Pool requires each entry to have approximately
   144  	// the same memory cost. To obtain this property when the stored type
   145  	// contains a variably-sized buffer, we add a hard limit on the maximum buffer
   146  	// to place back in the pool.
   147  	//
   148  	// See https://golang.org/issue/23199
   149  	if cap(p.buf) > 64<<10 {
   150  		return
   151  	}
   152  
   153  	p.buf = p.buf[:0]
   154  	p.arg = nil
   155  	p.value = reflect.Value{}
   156  	ppFree.Put(p)
   157  }
   158  
   159  func (p *pp) Width() (wid int, ok bool) { return p.fmt.wid, p.fmt.widPresent }
   160  
   161  func (p *pp) Precision() (prec int, ok bool) { return p.fmt.prec, p.fmt.precPresent }
   162  
   163  func (p *pp) Flag(b int) bool {
   164  	switch b {
   165  	case '-':
   166  		return p.fmt.minus
   167  	case '+':
   168  		return p.fmt.plus || p.fmt.plusV
   169  	case '#':
   170  		return p.fmt.sharp || p.fmt.sharpV
   171  	case ' ':
   172  		return p.fmt.space
   173  	case '0':
   174  		return p.fmt.zero
   175  	}
   176  	return false
   177  }
   178  
   179  // Implement Write so we can call Fprintf on a pp (through State), for
   180  // recursive use in custom verbs.
   181  func (p *pp) Write(b []byte) (ret int, err error) {
   182  	p.buf.Write(b)
   183  	return len(b), nil
   184  }
   185  
   186  // Implement WriteString so that we can call io.WriteString
   187  // on a pp (through state), for efficiency.
   188  func (p *pp) WriteString(s string) (ret int, err error) {
   189  	p.buf.WriteString(s)
   190  	return len(s), nil
   191  }
   192  
   193  // These routines end in 'f' and take a format string.
   194  
   195  // Fprintf formats according to a format specifier and writes to w.
   196  // It returns the number of bytes written and any write error encountered.
   197  func Fprintf(w io.Writer, format string, a ...interface{}) (n int, err error) {
   198  	p := newPrinter()
   199  	p.doPrintf(format, a)
   200  	n, err = w.Write(p.buf)
   201  	p.free()
   202  	return
   203  }
   204  
   205  // Printf formats according to a format specifier and writes to standard output.
   206  // It returns the number of bytes written and any write error encountered.
   207  func Printf(format string, a ...interface{}) (n int, err error) {
   208  	return Fprintf(os.Stdout, format, a...)
   209  }
   210  
   211  // Sprintf formats according to a format specifier and returns the resulting string.
   212  func Sprintf(format string, a ...interface{}) string {
   213  	p := newPrinter()
   214  	p.doPrintf(format, a)
   215  	s := string(p.buf)
   216  	p.free()
   217  	return s
   218  }
   219  
   220  // Errorf formats according to a format specifier and returns the string
   221  // as a value that satisfies error.
   222  func Errorf(format string, a ...interface{}) error {
   223  	return errors.New(Sprintf(format, a...))
   224  }
   225  
   226  // These routines do not take a format string
   227  
   228  // Fprint formats using the default formats for its operands and writes to w.
   229  // Spaces are added between operands when neither is a string.
   230  // It returns the number of bytes written and any write error encountered.
   231  func Fprint(w io.Writer, a ...interface{}) (n int, err error) {
   232  	p := newPrinter()
   233  	p.doPrint(a)
   234  	n, err = w.Write(p.buf)
   235  	p.free()
   236  	return
   237  }
   238  
   239  // Print formats using the default formats for its operands and writes to standard output.
   240  // Spaces are added between operands when neither is a string.
   241  // It returns the number of bytes written and any write error encountered.
   242  func Print(a ...interface{}) (n int, err error) {
   243  	return Fprint(os.Stdout, a...)
   244  }
   245  
   246  // Sprint formats using the default formats for its operands and returns the resulting string.
   247  // Spaces are added between operands when neither is a string.
   248  func Sprint(a ...interface{}) string {
   249  	p := newPrinter()
   250  	p.doPrint(a)
   251  	s := string(p.buf)
   252  	p.free()
   253  	return s
   254  }
   255  
   256  // These routines end in 'ln', do not take a format string,
   257  // always add spaces between operands, and add a newline
   258  // after the last operand.
   259  
   260  // Fprintln formats using the default formats for its operands and writes to w.
   261  // Spaces are always added between operands and a newline is appended.
   262  // It returns the number of bytes written and any write error encountered.
   263  func Fprintln(w io.Writer, a ...interface{}) (n int, err error) {
   264  	p := newPrinter()
   265  	p.doPrintln(a)
   266  	n, err = w.Write(p.buf)
   267  	p.free()
   268  	return
   269  }
   270  
   271  // Println formats using the default formats for its operands and writes to standard output.
   272  // Spaces are always added between operands and a newline is appended.
   273  // It returns the number of bytes written and any write error encountered.
   274  func Println(a ...interface{}) (n int, err error) {
   275  	return Fprintln(os.Stdout, a...)
   276  }
   277  
   278  // Sprintln formats using the default formats for its operands and returns the resulting string.
   279  // Spaces are always added between operands and a newline is appended.
   280  func Sprintln(a ...interface{}) string {
   281  	p := newPrinter()
   282  	p.doPrintln(a)
   283  	s := string(p.buf)
   284  	p.free()
   285  	return s
   286  }
   287  
   288  // getField gets the i'th field of the struct value.
   289  // If the field is itself is an interface, return a value for
   290  // the thing inside the interface, not the interface itself.
   291  func getField(v reflect.Value, i int) reflect.Value {
   292  	val := v.Field(i)
   293  	if val.Kind() == reflect.Interface && !val.IsNil() {
   294  		val = val.Elem()
   295  	}
   296  	return val
   297  }
   298  
   299  // tooLarge reports whether the magnitude of the integer is
   300  // too large to be used as a formatting width or precision.
   301  func tooLarge(x int) bool {
   302  	const max int = 1e6
   303  	return x > max || x < -max
   304  }
   305  
   306  // parsenum converts ASCII to integer.  num is 0 (and isnum is false) if no number present.
   307  func parsenum(s string, start, end int) (num int, isnum bool, newi int) {
   308  	if start >= end {
   309  		return 0, false, end
   310  	}
   311  	for newi = start; newi < end && '0' <= s[newi] && s[newi] <= '9'; newi++ {
   312  		if tooLarge(num) {
   313  			return 0, false, end // Overflow; crazy long number most likely.
   314  		}
   315  		num = num*10 + int(s[newi]-'0')
   316  		isnum = true
   317  	}
   318  	return
   319  }
   320  
   321  func (p *pp) unknownType(v reflect.Value) {
   322  	if !v.IsValid() {
   323  		p.buf.WriteString(nilAngleString)
   324  		return
   325  	}
   326  	p.buf.WriteByte('?')
   327  	p.buf.WriteString(v.Type().String())
   328  	p.buf.WriteByte('?')
   329  }
   330  
   331  func (p *pp) badVerb(verb rune) {
   332  	p.erroring = true
   333  	p.buf.WriteString(percentBangString)
   334  	p.buf.WriteRune(verb)
   335  	p.buf.WriteByte('(')
   336  	switch {
   337  	case p.arg != nil:
   338  		p.buf.WriteString(reflect.TypeOf(p.arg).String())
   339  		p.buf.WriteByte('=')
   340  		p.printArg(p.arg, 'v')
   341  	case p.value.IsValid():
   342  		p.buf.WriteString(p.value.Type().String())
   343  		p.buf.WriteByte('=')
   344  		p.printValue(p.value, 'v', 0)
   345  	default:
   346  		p.buf.WriteString(nilAngleString)
   347  	}
   348  	p.buf.WriteByte(')')
   349  	p.erroring = false
   350  }
   351  
   352  func (p *pp) fmtBool(v bool, verb rune) {
   353  	switch verb {
   354  	case 't', 'v':
   355  		p.fmt.fmtBoolean(v)
   356  	default:
   357  		p.badVerb(verb)
   358  	}
   359  }
   360  
   361  // fmt0x64 formats a uint64 in hexadecimal and prefixes it with 0x or
   362  // not, as requested, by temporarily setting the sharp flag.
   363  func (p *pp) fmt0x64(v uint64, leading0x bool) {
   364  	sharp := p.fmt.sharp
   365  	p.fmt.sharp = leading0x
   366  	p.fmt.fmtInteger(v, 16, unsigned, ldigits)
   367  	p.fmt.sharp = sharp
   368  }
   369  
   370  // fmtInteger formats a signed or unsigned integer.
   371  func (p *pp) fmtInteger(v uint64, isSigned bool, verb rune) {
   372  	switch verb {
   373  	case 'v':
   374  		if p.fmt.sharpV && !isSigned {
   375  			p.fmt0x64(v, true)
   376  		} else {
   377  			p.fmt.fmtInteger(v, 10, isSigned, ldigits)
   378  		}
   379  	case 'd':
   380  		p.fmt.fmtInteger(v, 10, isSigned, ldigits)
   381  	case 'b':
   382  		p.fmt.fmtInteger(v, 2, isSigned, ldigits)
   383  	case 'o':
   384  		p.fmt.fmtInteger(v, 8, isSigned, ldigits)
   385  	case 'x':
   386  		p.fmt.fmtInteger(v, 16, isSigned, ldigits)
   387  	case 'X':
   388  		p.fmt.fmtInteger(v, 16, isSigned, udigits)
   389  	case 'c':
   390  		p.fmt.fmtC(v)
   391  	case 'q':
   392  		if v <= utf8.MaxRune {
   393  			p.fmt.fmtQc(v)
   394  		} else {
   395  			p.badVerb(verb)
   396  		}
   397  	case 'U':
   398  		p.fmt.fmtUnicode(v)
   399  	default:
   400  		p.badVerb(verb)
   401  	}
   402  }
   403  
   404  // fmtFloat formats a float. The default precision for each verb
   405  // is specified as last argument in the call to fmt_float.
   406  func (p *pp) fmtFloat(v float64, size int, verb rune) {
   407  	switch verb {
   408  	case 'v':
   409  		p.fmt.fmtFloat(v, size, 'g', -1)
   410  	case 'b', 'g', 'G':
   411  		p.fmt.fmtFloat(v, size, verb, -1)
   412  	case 'f', 'e', 'E':
   413  		p.fmt.fmtFloat(v, size, verb, 6)
   414  	case 'F':
   415  		p.fmt.fmtFloat(v, size, 'f', 6)
   416  	default:
   417  		p.badVerb(verb)
   418  	}
   419  }
   420  
   421  // fmtComplex formats a complex number v with
   422  // r = real(v) and j = imag(v) as (r+ji) using
   423  // fmtFloat for r and j formatting.
   424  func (p *pp) fmtComplex(v complex128, size int, verb rune) {
   425  	// Make sure any unsupported verbs are found before the
   426  	// calls to fmtFloat to not generate an incorrect error string.
   427  	switch verb {
   428  	case 'v', 'b', 'g', 'G', 'f', 'F', 'e', 'E':
   429  		oldPlus := p.fmt.plus
   430  		p.buf.WriteByte('(')
   431  		p.fmtFloat(real(v), size/2, verb)
   432  		// Imaginary part always has a sign.
   433  		p.fmt.plus = true
   434  		p.fmtFloat(imag(v), size/2, verb)
   435  		p.buf.WriteString("i)")
   436  		p.fmt.plus = oldPlus
   437  	default:
   438  		p.badVerb(verb)
   439  	}
   440  }
   441  
   442  func (p *pp) fmtString(v string, verb rune) {
   443  	switch verb {
   444  	case 'v':
   445  		if p.fmt.sharpV {
   446  			p.fmt.fmtQ(v)
   447  		} else {
   448  			p.fmt.fmtS(v)
   449  		}
   450  	case 's':
   451  		p.fmt.fmtS(v)
   452  	case 'x':
   453  		p.fmt.fmtSx(v, ldigits)
   454  	case 'X':
   455  		p.fmt.fmtSx(v, udigits)
   456  	case 'q':
   457  		p.fmt.fmtQ(v)
   458  	default:
   459  		p.badVerb(verb)
   460  	}
   461  }
   462  
   463  func (p *pp) fmtBytes(v []byte, verb rune, typeString string) {
   464  	switch verb {
   465  	case 'v', 'd':
   466  		if p.fmt.sharpV {
   467  			p.buf.WriteString(typeString)
   468  			if v == nil {
   469  				p.buf.WriteString(nilParenString)
   470  				return
   471  			}
   472  			p.buf.WriteByte('{')
   473  			for i, c := range v {
   474  				if i > 0 {
   475  					p.buf.WriteString(commaSpaceString)
   476  				}
   477  				p.fmt0x64(uint64(c), true)
   478  			}
   479  			p.buf.WriteByte('}')
   480  		} else {
   481  			p.buf.WriteByte('[')
   482  			for i, c := range v {
   483  				if i > 0 {
   484  					p.buf.WriteByte(' ')
   485  				}
   486  				p.fmt.fmtInteger(uint64(c), 10, unsigned, ldigits)
   487  			}
   488  			p.buf.WriteByte(']')
   489  		}
   490  	case 's':
   491  		p.fmt.fmtBs(v)
   492  	case 'x':
   493  		p.fmt.fmtBx(v, ldigits)
   494  	case 'X':
   495  		p.fmt.fmtBx(v, udigits)
   496  	case 'q':
   497  		p.fmt.fmtQ(string(v))
   498  	default:
   499  		p.printValue(reflect.ValueOf(v), verb, 0)
   500  	}
   501  }
   502  
   503  func (p *pp) fmtPointer(value reflect.Value, verb rune) {
   504  	var u uintptr
   505  	switch value.Kind() {
   506  	case reflect.Chan, reflect.Func, reflect.Map, reflect.Ptr, reflect.Slice, reflect.UnsafePointer:
   507  		u = value.Pointer()
   508  	default:
   509  		p.badVerb(verb)
   510  		return
   511  	}
   512  
   513  	switch verb {
   514  	case 'v':
   515  		if p.fmt.sharpV {
   516  			p.buf.WriteByte('(')
   517  			p.buf.WriteString(value.Type().String())
   518  			p.buf.WriteString(")(")
   519  			if u == 0 {
   520  				p.buf.WriteString(nilString)
   521  			} else {
   522  				p.fmt0x64(uint64(u), true)
   523  			}
   524  			p.buf.WriteByte(')')
   525  		} else {
   526  			if u == 0 {
   527  				p.fmt.padString(nilAngleString)
   528  			} else {
   529  				p.fmt0x64(uint64(u), !p.fmt.sharp)
   530  			}
   531  		}
   532  	case 'p':
   533  		p.fmt0x64(uint64(u), !p.fmt.sharp)
   534  	case 'b', 'o', 'd', 'x', 'X':
   535  		p.fmtInteger(uint64(u), unsigned, verb)
   536  	default:
   537  		p.badVerb(verb)
   538  	}
   539  }
   540  
   541  func (p *pp) catchPanic(arg interface{}, verb rune, method string) {
   542  	if err := recover(); err != nil {
   543  		// If it's a nil pointer, just say "<nil>". The likeliest causes are a
   544  		// Stringer that fails to guard against nil or a nil pointer for a
   545  		// value receiver, and in either case, "<nil>" is a nice result.
   546  		if v := reflect.ValueOf(arg); v.Kind() == reflect.Ptr && v.IsNil() {
   547  			p.buf.WriteString(nilAngleString)
   548  			return
   549  		}
   550  		// Otherwise print a concise panic message. Most of the time the panic
   551  		// value will print itself nicely.
   552  		if p.panicking {
   553  			// Nested panics; the recursion in printArg cannot succeed.
   554  			panic(err)
   555  		}
   556  
   557  		oldFlags := p.fmt.fmtFlags
   558  		// For this output we want default behavior.
   559  		p.fmt.clearflags()
   560  
   561  		p.buf.WriteString(percentBangString)
   562  		p.buf.WriteRune(verb)
   563  		p.buf.WriteString(panicString)
   564  		p.buf.WriteString(method)
   565  		p.buf.WriteString(" method: ")
   566  		p.panicking = true
   567  		p.printArg(err, 'v')
   568  		p.panicking = false
   569  		p.buf.WriteByte(')')
   570  
   571  		p.fmt.fmtFlags = oldFlags
   572  	}
   573  }
   574  
   575  func (p *pp) handleMethods(verb rune) (handled bool) {
   576  	if p.erroring {
   577  		return
   578  	}
   579  	// Is it a Formatter?
   580  	if formatter, ok := p.arg.(Formatter); ok {
   581  		handled = true
   582  		defer p.catchPanic(p.arg, verb, "Format")
   583  		formatter.Format(p, verb)
   584  		return
   585  	}
   586  
   587  	// If we're doing Go syntax and the argument knows how to supply it, take care of it now.
   588  	if p.fmt.sharpV {
   589  		if stringer, ok := p.arg.(GoStringer); ok {
   590  			handled = true
   591  			defer p.catchPanic(p.arg, verb, "GoString")
   592  			// Print the result of GoString unadorned.
   593  			p.fmt.fmtS(stringer.GoString())
   594  			return
   595  		}
   596  	} else {
   597  		// If a string is acceptable according to the format, see if
   598  		// the value satisfies one of the string-valued interfaces.
   599  		// Println etc. set verb to %v, which is "stringable".
   600  		switch verb {
   601  		case 'v', 's', 'x', 'X', 'q':
   602  			// Is it an error or Stringer?
   603  			// The duplication in the bodies is necessary:
   604  			// setting handled and deferring catchPanic
   605  			// must happen before calling the method.
   606  			switch v := p.arg.(type) {
   607  			case error:
   608  				handled = true
   609  				defer p.catchPanic(p.arg, verb, "Error")
   610  				p.fmtString(v.Error(), verb)
   611  				return
   612  
   613  			case Stringer:
   614  				handled = true
   615  				defer p.catchPanic(p.arg, verb, "String")
   616  				p.fmtString(v.String(), verb)
   617  				return
   618  			}
   619  		}
   620  	}
   621  	return false
   622  }
   623  
   624  func (p *pp) printArg(arg interface{}, verb rune) {
   625  	p.arg = arg
   626  	p.value = reflect.Value{}
   627  
   628  	if arg == nil {
   629  		switch verb {
   630  		case 'T', 'v':
   631  			p.fmt.padString(nilAngleString)
   632  		default:
   633  			p.badVerb(verb)
   634  		}
   635  		return
   636  	}
   637  
   638  	// Special processing considerations.
   639  	// %T (the value's type) and %p (its address) are special; we always do them first.
   640  	switch verb {
   641  	case 'T':
   642  		p.fmt.fmtS(reflect.TypeOf(arg).String())
   643  		return
   644  	case 'p':
   645  		p.fmtPointer(reflect.ValueOf(arg), 'p')
   646  		return
   647  	}
   648  
   649  	// Some types can be done without reflection.
   650  	switch f := arg.(type) {
   651  	case bool:
   652  		p.fmtBool(f, verb)
   653  	case float32:
   654  		p.fmtFloat(float64(f), 32, verb)
   655  	case float64:
   656  		p.fmtFloat(f, 64, verb)
   657  	case complex64:
   658  		p.fmtComplex(complex128(f), 64, verb)
   659  	case complex128:
   660  		p.fmtComplex(f, 128, verb)
   661  	case int:
   662  		p.fmtInteger(uint64(f), signed, verb)
   663  	case int8:
   664  		p.fmtInteger(uint64(f), signed, verb)
   665  	case int16:
   666  		p.fmtInteger(uint64(f), signed, verb)
   667  	case int32:
   668  		p.fmtInteger(uint64(f), signed, verb)
   669  	case int64:
   670  		p.fmtInteger(uint64(f), signed, verb)
   671  	case uint:
   672  		p.fmtInteger(uint64(f), unsigned, verb)
   673  	case uint8:
   674  		p.fmtInteger(uint64(f), unsigned, verb)
   675  	case uint16:
   676  		p.fmtInteger(uint64(f), unsigned, verb)
   677  	case uint32:
   678  		p.fmtInteger(uint64(f), unsigned, verb)
   679  	case uint64:
   680  		p.fmtInteger(f, unsigned, verb)
   681  	case uintptr:
   682  		p.fmtInteger(uint64(f), unsigned, verb)
   683  	case string:
   684  		p.fmtString(f, verb)
   685  	case []byte:
   686  		p.fmtBytes(f, verb, "[]byte")
   687  	case reflect.Value:
   688  		// Handle extractable values with special methods
   689  		// since printValue does not handle them at depth 0.
   690  		if f.IsValid() && f.CanInterface() {
   691  			p.arg = f.Interface()
   692  			if p.handleMethods(verb) {
   693  				return
   694  			}
   695  		}
   696  		p.printValue(f, verb, 0)
   697  	default:
   698  		// If the type is not simple, it might have methods.
   699  		if !p.handleMethods(verb) {
   700  			// Need to use reflection, since the type had no
   701  			// interface methods that could be used for formatting.
   702  			p.printValue(reflect.ValueOf(f), verb, 0)
   703  		}
   704  	}
   705  }
   706  
   707  // printValue is similar to printArg but starts with a reflect value, not an interface{} value.
   708  // It does not handle 'p' and 'T' verbs because these should have been already handled by printArg.
   709  func (p *pp) printValue(value reflect.Value, verb rune, depth int) {
   710  	// Handle values with special methods if not already handled by printArg (depth == 0).
   711  	if depth > 0 && value.IsValid() && value.CanInterface() {
   712  		p.arg = value.Interface()
   713  		if p.handleMethods(verb) {
   714  			return
   715  		}
   716  	}
   717  	p.arg = nil
   718  	p.value = value
   719  
   720  	switch f := value; value.Kind() {
   721  	case reflect.Invalid:
   722  		if depth == 0 {
   723  			p.buf.WriteString(invReflectString)
   724  		} else {
   725  			switch verb {
   726  			case 'v':
   727  				p.buf.WriteString(nilAngleString)
   728  			default:
   729  				p.badVerb(verb)
   730  			}
   731  		}
   732  	case reflect.Bool:
   733  		p.fmtBool(f.Bool(), verb)
   734  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   735  		p.fmtInteger(uint64(f.Int()), signed, verb)
   736  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   737  		p.fmtInteger(f.Uint(), unsigned, verb)
   738  	case reflect.Float32:
   739  		p.fmtFloat(f.Float(), 32, verb)
   740  	case reflect.Float64:
   741  		p.fmtFloat(f.Float(), 64, verb)
   742  	case reflect.Complex64:
   743  		p.fmtComplex(f.Complex(), 64, verb)
   744  	case reflect.Complex128:
   745  		p.fmtComplex(f.Complex(), 128, verb)
   746  	case reflect.String:
   747  		p.fmtString(f.String(), verb)
   748  	case reflect.Map:
   749  		if p.fmt.sharpV {
   750  			p.buf.WriteString(f.Type().String())
   751  			if f.IsNil() {
   752  				p.buf.WriteString(nilParenString)
   753  				return
   754  			}
   755  			p.buf.WriteByte('{')
   756  		} else {
   757  			p.buf.WriteString(mapString)
   758  		}
   759  		sorted := fmtsort.Sort(f)
   760  		for i, key := range sorted.Key {
   761  			if i > 0 {
   762  				if p.fmt.sharpV {
   763  					p.buf.WriteString(commaSpaceString)
   764  				} else {
   765  					p.buf.WriteByte(' ')
   766  				}
   767  			}
   768  			p.printValue(key, verb, depth+1)
   769  			p.buf.WriteByte(':')
   770  			p.printValue(sorted.Value[i], verb, depth+1)
   771  		}
   772  		if p.fmt.sharpV {
   773  			p.buf.WriteByte('}')
   774  		} else {
   775  			p.buf.WriteByte(']')
   776  		}
   777  	case reflect.Struct:
   778  		if p.fmt.sharpV {
   779  			p.buf.WriteString(f.Type().String())
   780  		}
   781  		p.buf.WriteByte('{')
   782  		for i := 0; i < f.NumField(); i++ {
   783  			if i > 0 {
   784  				if p.fmt.sharpV {
   785  					p.buf.WriteString(commaSpaceString)
   786  				} else {
   787  					p.buf.WriteByte(' ')
   788  				}
   789  			}
   790  			if p.fmt.plusV || p.fmt.sharpV {
   791  				if name := f.Type().Field(i).Name; name != "" {
   792  					p.buf.WriteString(name)
   793  					p.buf.WriteByte(':')
   794  				}
   795  			}
   796  			p.printValue(getField(f, i), verb, depth+1)
   797  		}
   798  		p.buf.WriteByte('}')
   799  	case reflect.Interface:
   800  		value := f.Elem()
   801  		if !value.IsValid() {
   802  			if p.fmt.sharpV {
   803  				p.buf.WriteString(f.Type().String())
   804  				p.buf.WriteString(nilParenString)
   805  			} else {
   806  				p.buf.WriteString(nilAngleString)
   807  			}
   808  		} else {
   809  			p.printValue(value, verb, depth+1)
   810  		}
   811  	case reflect.Array, reflect.Slice:
   812  		switch verb {
   813  		case 's', 'q', 'x', 'X':
   814  			// Handle byte and uint8 slices and arrays special for the above verbs.
   815  			t := f.Type()
   816  			if t.Elem().Kind() == reflect.Uint8 {
   817  				var bytes []byte
   818  				if f.Kind() == reflect.Slice {
   819  					bytes = f.Bytes()
   820  				} else if f.CanAddr() {
   821  					bytes = f.Slice(0, f.Len()).Bytes()
   822  				} else {
   823  					// We have an array, but we cannot Slice() a non-addressable array,
   824  					// so we build a slice by hand. This is a rare case but it would be nice
   825  					// if reflection could help a little more.
   826  					bytes = make([]byte, f.Len())
   827  					for i := range bytes {
   828  						bytes[i] = byte(f.Index(i).Uint())
   829  					}
   830  				}
   831  				p.fmtBytes(bytes, verb, t.String())
   832  				return
   833  			}
   834  		}
   835  		if p.fmt.sharpV {
   836  			p.buf.WriteString(f.Type().String())
   837  			if f.Kind() == reflect.Slice && f.IsNil() {
   838  				p.buf.WriteString(nilParenString)
   839  				return
   840  			}
   841  			p.buf.WriteByte('{')
   842  			for i := 0; i < f.Len(); i++ {
   843  				if i > 0 {
   844  					p.buf.WriteString(commaSpaceString)
   845  				}
   846  				p.printValue(f.Index(i), verb, depth+1)
   847  			}
   848  			p.buf.WriteByte('}')
   849  		} else {
   850  			p.buf.WriteByte('[')
   851  			for i := 0; i < f.Len(); i++ {
   852  				if i > 0 {
   853  					p.buf.WriteByte(' ')
   854  				}
   855  				p.printValue(f.Index(i), verb, depth+1)
   856  			}
   857  			p.buf.WriteByte(']')
   858  		}
   859  	case reflect.Ptr:
   860  		// pointer to array or slice or struct? ok at top level
   861  		// but not embedded (avoid loops)
   862  		if depth == 0 && f.Pointer() != 0 {
   863  			switch a := f.Elem(); a.Kind() {
   864  			case reflect.Array, reflect.Slice, reflect.Struct, reflect.Map:
   865  				p.buf.WriteByte('&')
   866  				p.printValue(a, verb, depth+1)
   867  				return
   868  			}
   869  		}
   870  		fallthrough
   871  	case reflect.Chan, reflect.Func, reflect.UnsafePointer:
   872  		p.fmtPointer(f, verb)
   873  	default:
   874  		p.unknownType(f)
   875  	}
   876  }
   877  
   878  // intFromArg gets the argNumth element of a. On return, isInt reports whether the argument has integer type.
   879  func intFromArg(a []interface{}, argNum int) (num int, isInt bool, newArgNum int) {
   880  	newArgNum = argNum
   881  	if argNum < len(a) {
   882  		num, isInt = a[argNum].(int) // Almost always OK.
   883  		if !isInt {
   884  			// Work harder.
   885  			switch v := reflect.ValueOf(a[argNum]); v.Kind() {
   886  			case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   887  				n := v.Int()
   888  				if int64(int(n)) == n {
   889  					num = int(n)
   890  					isInt = true
   891  				}
   892  			case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   893  				n := v.Uint()
   894  				if int64(n) >= 0 && uint64(int(n)) == n {
   895  					num = int(n)
   896  					isInt = true
   897  				}
   898  			default:
   899  				// Already 0, false.
   900  			}
   901  		}
   902  		newArgNum = argNum + 1
   903  		if tooLarge(num) {
   904  			num = 0
   905  			isInt = false
   906  		}
   907  	}
   908  	return
   909  }
   910  
   911  // parseArgNumber returns the value of the bracketed number, minus 1
   912  // (explicit argument numbers are one-indexed but we want zero-indexed).
   913  // The opening bracket is known to be present at format[0].
   914  // The returned values are the index, the number of bytes to consume
   915  // up to the closing paren, if present, and whether the number parsed
   916  // ok. The bytes to consume will be 1 if no closing paren is present.
   917  func parseArgNumber(format string) (index int, wid int, ok bool) {
   918  	// There must be at least 3 bytes: [n].
   919  	if len(format) < 3 {
   920  		return 0, 1, false
   921  	}
   922  
   923  	// Find closing bracket.
   924  	for i := 1; i < len(format); i++ {
   925  		if format[i] == ']' {
   926  			width, ok, newi := parsenum(format, 1, i)
   927  			if !ok || newi != i {
   928  				return 0, i + 1, false
   929  			}
   930  			return width - 1, i + 1, true // arg numbers are one-indexed and skip paren.
   931  		}
   932  	}
   933  	return 0, 1, false
   934  }
   935  
   936  // argNumber returns the next argument to evaluate, which is either the value of the passed-in
   937  // argNum or the value of the bracketed integer that begins format[i:]. It also returns
   938  // the new value of i, that is, the index of the next byte of the format to process.
   939  func (p *pp) argNumber(argNum int, format string, i int, numArgs int) (newArgNum, newi int, found bool) {
   940  	if len(format) <= i || format[i] != '[' {
   941  		return argNum, i, false
   942  	}
   943  	p.reordered = true
   944  	index, wid, ok := parseArgNumber(format[i:])
   945  	if ok && 0 <= index && index < numArgs {
   946  		return index, i + wid, true
   947  	}
   948  	p.goodArgNum = false
   949  	return argNum, i + wid, ok
   950  }
   951  
   952  func (p *pp) badArgNum(verb rune) {
   953  	p.buf.WriteString(percentBangString)
   954  	p.buf.WriteRune(verb)
   955  	p.buf.WriteString(badIndexString)
   956  }
   957  
   958  func (p *pp) missingArg(verb rune) {
   959  	p.buf.WriteString(percentBangString)
   960  	p.buf.WriteRune(verb)
   961  	p.buf.WriteString(missingString)
   962  }
   963  
   964  func (p *pp) doPrintf(format string, a []interface{}) {
   965  	end := len(format)
   966  	argNum := 0         // we process one argument per non-trivial format
   967  	afterIndex := false // previous item in format was an index like [3].
   968  	p.reordered = false
   969  formatLoop:
   970  	for i := 0; i < end; {
   971  		p.goodArgNum = true
   972  		lasti := i
   973  		for i < end && format[i] != '%' {
   974  			i++
   975  		}
   976  		if i > lasti {
   977  			p.buf.WriteString(format[lasti:i])
   978  		}
   979  		if i >= end {
   980  			// done processing format string
   981  			break
   982  		}
   983  
   984  		// Process one verb
   985  		i++
   986  
   987  		// Do we have flags?
   988  		p.fmt.clearflags()
   989  	simpleFormat:
   990  		for ; i < end; i++ {
   991  			c := format[i]
   992  			switch c {
   993  			case '#':
   994  				p.fmt.sharp = true
   995  			case '0':
   996  				p.fmt.zero = !p.fmt.minus // Only allow zero padding to the left.
   997  			case '+':
   998  				p.fmt.plus = true
   999  			case '-':
  1000  				p.fmt.minus = true
  1001  				p.fmt.zero = false // Do not pad with zeros to the right.
  1002  			case ' ':
  1003  				p.fmt.space = true
  1004  			default:
  1005  				// Fast path for common case of ascii lower case simple verbs
  1006  				// without precision or width or argument indices.
  1007  				if 'a' <= c && c <= 'z' && argNum < len(a) {
  1008  					if c == 'v' {
  1009  						// Go syntax
  1010  						p.fmt.sharpV = p.fmt.sharp
  1011  						p.fmt.sharp = false
  1012  						// Struct-field syntax
  1013  						p.fmt.plusV = p.fmt.plus
  1014  						p.fmt.plus = false
  1015  					}
  1016  					p.printArg(a[argNum], rune(c))
  1017  					argNum++
  1018  					i++
  1019  					continue formatLoop
  1020  				}
  1021  				// Format is more complex than simple flags and a verb or is malformed.
  1022  				break simpleFormat
  1023  			}
  1024  		}
  1025  
  1026  		// Do we have an explicit argument index?
  1027  		argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
  1028  
  1029  		// Do we have width?
  1030  		if i < end && format[i] == '*' {
  1031  			i++
  1032  			p.fmt.wid, p.fmt.widPresent, argNum = intFromArg(a, argNum)
  1033  
  1034  			if !p.fmt.widPresent {
  1035  				p.buf.WriteString(badWidthString)
  1036  			}
  1037  
  1038  			// We have a negative width, so take its value and ensure
  1039  			// that the minus flag is set
  1040  			if p.fmt.wid < 0 {
  1041  				p.fmt.wid = -p.fmt.wid
  1042  				p.fmt.minus = true
  1043  				p.fmt.zero = false // Do not pad with zeros to the right.
  1044  			}
  1045  			afterIndex = false
  1046  		} else {
  1047  			p.fmt.wid, p.fmt.widPresent, i = parsenum(format, i, end)
  1048  			if afterIndex && p.fmt.widPresent { // "%[3]2d"
  1049  				p.goodArgNum = false
  1050  			}
  1051  		}
  1052  
  1053  		// Do we have precision?
  1054  		if i+1 < end && format[i] == '.' {
  1055  			i++
  1056  			if afterIndex { // "%[3].2d"
  1057  				p.goodArgNum = false
  1058  			}
  1059  			argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
  1060  			if i < end && format[i] == '*' {
  1061  				i++
  1062  				p.fmt.prec, p.fmt.precPresent, argNum = intFromArg(a, argNum)
  1063  				// Negative precision arguments don't make sense
  1064  				if p.fmt.prec < 0 {
  1065  					p.fmt.prec = 0
  1066  					p.fmt.precPresent = false
  1067  				}
  1068  				if !p.fmt.precPresent {
  1069  					p.buf.WriteString(badPrecString)
  1070  				}
  1071  				afterIndex = false
  1072  			} else {
  1073  				p.fmt.prec, p.fmt.precPresent, i = parsenum(format, i, end)
  1074  				if !p.fmt.precPresent {
  1075  					p.fmt.prec = 0
  1076  					p.fmt.precPresent = true
  1077  				}
  1078  			}
  1079  		}
  1080  
  1081  		if !afterIndex {
  1082  			argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
  1083  		}
  1084  
  1085  		if i >= end {
  1086  			p.buf.WriteString(noVerbString)
  1087  			break
  1088  		}
  1089  
  1090  		verb, size := rune(format[i]), 1
  1091  		if verb >= utf8.RuneSelf {
  1092  			verb, size = utf8.DecodeRuneInString(format[i:])
  1093  		}
  1094  		i += size
  1095  
  1096  		switch {
  1097  		case verb == '%': // Percent does not absorb operands and ignores f.wid and f.prec.
  1098  			p.buf.WriteByte('%')
  1099  		case !p.goodArgNum:
  1100  			p.badArgNum(verb)
  1101  		case argNum >= len(a): // No argument left over to print for the current verb.
  1102  			p.missingArg(verb)
  1103  		case verb == 'v':
  1104  			// Go syntax
  1105  			p.fmt.sharpV = p.fmt.sharp
  1106  			p.fmt.sharp = false
  1107  			// Struct-field syntax
  1108  			p.fmt.plusV = p.fmt.plus
  1109  			p.fmt.plus = false
  1110  			fallthrough
  1111  		default:
  1112  			p.printArg(a[argNum], verb)
  1113  			argNum++
  1114  		}
  1115  	}
  1116  
  1117  	// Check for extra arguments unless the call accessed the arguments
  1118  	// out of order, in which case it's too expensive to detect if they've all
  1119  	// been used and arguably OK if they're not.
  1120  	if !p.reordered && argNum < len(a) {
  1121  		p.fmt.clearflags()
  1122  		p.buf.WriteString(extraString)
  1123  		for i, arg := range a[argNum:] {
  1124  			if i > 0 {
  1125  				p.buf.WriteString(commaSpaceString)
  1126  			}
  1127  			if arg == nil {
  1128  				p.buf.WriteString(nilAngleString)
  1129  			} else {
  1130  				p.buf.WriteString(reflect.TypeOf(arg).String())
  1131  				p.buf.WriteByte('=')
  1132  				p.printArg(arg, 'v')
  1133  			}
  1134  		}
  1135  		p.buf.WriteByte(')')
  1136  	}
  1137  }
  1138  
  1139  func (p *pp) doPrint(a []interface{}) {
  1140  	prevString := false
  1141  	for argNum, arg := range a {
  1142  		isString := arg != nil && reflect.TypeOf(arg).Kind() == reflect.String
  1143  		// Add a space between two non-string arguments.
  1144  		if argNum > 0 && !isString && !prevString {
  1145  			p.buf.WriteByte(' ')
  1146  		}
  1147  		p.printArg(arg, 'v')
  1148  		prevString = isString
  1149  	}
  1150  }
  1151  
  1152  // doPrintln is like doPrint but always adds a space between arguments
  1153  // and a newline after the last argument.
  1154  func (p *pp) doPrintln(a []interface{}) {
  1155  	for argNum, arg := range a {
  1156  		if argNum > 0 {
  1157  			p.buf.WriteByte(' ')
  1158  		}
  1159  		p.printArg(arg, 'v')
  1160  	}
  1161  	p.buf.WriteByte('\n')
  1162  }
  1163  

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