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Package reflect

import "reflect"
Overview
Index
Examples

Overview ▾

Package reflect implements run-time reflection, allowing a program to manipulate objects with arbitrary types. The typical use is to take a value with static type interface{} and extract its dynamic type information by calling TypeOf, which returns a Type.

A call to ValueOf returns a Value representing the run-time data. Zero takes a Type and returns a Value representing a zero value for that type.

See "The Laws of Reflection" for an introduction to reflection in Go: https://golang.org/doc/articles/laws_of_reflection.html

Index ▾

func Copy(dst, src Value) int
func DeepEqual(x, y interface{}) bool
func Select(cases []SelectCase) (chosen int, recv Value, recvOK bool)
type ChanDir
    func (d ChanDir) String() string
type Kind
    func (k Kind) String() string
type Method
type SelectCase
type SelectDir
type SliceHeader
type StringHeader
type StructField
type StructTag
    func (tag StructTag) Get(key string) string
    func (tag StructTag) Lookup(key string) (value string, ok bool)
type Type
    func ArrayOf(count int, elem Type) Type
    func ChanOf(dir ChanDir, t Type) Type
    func FuncOf(in, out []Type, variadic bool) Type
    func MapOf(key, elem Type) Type
    func PtrTo(t Type) Type
    func SliceOf(t Type) Type
    func StructOf(fields []StructField) Type
    func TypeOf(i interface{}) Type
type Value
    func Append(s Value, x ...Value) Value
    func AppendSlice(s, t Value) Value
    func Indirect(v Value) Value
    func MakeChan(typ Type, buffer int) Value
    func MakeFunc(typ Type, fn func(args []Value) (results []Value)) Value
    func MakeMap(typ Type) Value
    func MakeSlice(typ Type, len, cap int) Value
    func New(typ Type) Value
    func NewAt(typ Type, p unsafe.Pointer) Value
    func ValueOf(i interface{}) Value
    func Zero(typ Type) Value
    func (v Value) Addr() Value
    func (v Value) Bool() bool
    func (v Value) Bytes() []byte
    func (v Value) Call(in []Value) []Value
    func (v Value) CallSlice(in []Value) []Value
    func (v Value) CanAddr() bool
    func (v Value) CanInterface() bool
    func (v Value) CanSet() bool
    func (v Value) Cap() int
    func (v Value) Close()
    func (v Value) Complex() complex128
    func (v Value) Convert(t Type) Value
    func (v Value) Elem() Value
    func (v Value) Field(i int) Value
    func (v Value) FieldByIndex(index []int) Value
    func (v Value) FieldByName(name string) Value
    func (v Value) FieldByNameFunc(match func(string) bool) Value
    func (v Value) Float() float64
    func (v Value) Index(i int) Value
    func (v Value) Int() int64
    func (v Value) Interface() (i interface{})
    func (v Value) InterfaceData() [2]uintptr
    func (v Value) IsNil() bool
    func (v Value) IsValid() bool
    func (v Value) Kind() Kind
    func (v Value) Len() int
    func (v Value) MapIndex(key Value) Value
    func (v Value) MapKeys() []Value
    func (v Value) Method(i int) Value
    func (v Value) MethodByName(name string) Value
    func (v Value) NumField() int
    func (v Value) NumMethod() int
    func (v Value) OverflowComplex(x complex128) bool
    func (v Value) OverflowFloat(x float64) bool
    func (v Value) OverflowInt(x int64) bool
    func (v Value) OverflowUint(x uint64) bool
    func (v Value) Pointer() uintptr
    func (v Value) Recv() (x Value, ok bool)
    func (v Value) Send(x Value)
    func (v Value) Set(x Value)
    func (v Value) SetBool(x bool)
    func (v Value) SetBytes(x []byte)
    func (v Value) SetCap(n int)
    func (v Value) SetComplex(x complex128)
    func (v Value) SetFloat(x float64)
    func (v Value) SetInt(x int64)
    func (v Value) SetLen(n int)
    func (v Value) SetMapIndex(key, val Value)
    func (v Value) SetPointer(x unsafe.Pointer)
    func (v Value) SetString(x string)
    func (v Value) SetUint(x uint64)
    func (v Value) Slice(i, j int) Value
    func (v Value) Slice3(i, j, k int) Value
    func (v Value) String() string
    func (v Value) TryRecv() (x Value, ok bool)
    func (v Value) TrySend(x Value) bool
    func (v Value) Type() Type
    func (v Value) Uint() uint64
    func (v Value) UnsafeAddr() uintptr
type ValueError
    func (e *ValueError) Error() string
Bugs

Package files

deepequal.go makefunc.go type.go value.go

func Copy

Copy copies the contents of src into dst until either dst has been filled or src has been exhausted. It returns the number of elements copied. Dst and src each must have kind Slice or Array, and dst and src must have the same element type.

func Copy(dst, src Value) int

func DeepEqual

DeepEqual reports whether x and y are “deeply equal,” defined as follows. Two values of identical type are deeply equal if one of the following cases applies. Values of distinct types are never deeply equal.

Array values are deeply equal when their corresponding elements are deeply equal.

Struct values are deeply equal if their corresponding fields, both exported and unexported, are deeply equal.

Func values are deeply equal if both are nil; otherwise they are not deeply equal.

Interface values are deeply equal if they hold deeply equal concrete values.

Map values are deeply equal if they are the same map object or if they have the same length and their corresponding keys (matched using Go equality) map to deeply equal values.

Pointer values are deeply equal if they are equal using Go's == operator or if they point to deeply equal values.

Slice values are deeply equal when all of the following are true: they are both nil or both non-nil, they have the same length, and either they point to the same initial entry of the same underlying array (that is, &x[0] == &y[0]) or their corresponding elements (up to length) are deeply equal. Note that a non-nil empty slice and a nil slice (for example, []byte{} and []byte(nil)) are not deeply equal.

Other values - numbers, bools, strings, and channels - are deeply equal if they are equal using Go's == operator.

In general DeepEqual is a recursive relaxation of Go's == operator. However, this idea is impossible to implement without some inconsistency. Specifically, it is possible for a value to be unequal to itself, either because it is of func type (uncomparable in general) or because it is a floating-point NaN value (not equal to itself in floating-point comparison), or because it is an array, struct, or interface containing such a value. On the other hand, pointer values are always equal to themselves, even if they point at or contain such problematic values, because they compare equal using Go's == operator, and that is a sufficient condition to be deeply equal, regardless of content. DeepEqual has been defined so that the same short-cut applies to slices and maps: if x and y are the same slice or the same map, they are deeply equal regardless of content.

func DeepEqual(x, y interface{}) bool

func Select

Select executes a select operation described by the list of cases. Like the Go select statement, it blocks until at least one of the cases can proceed, makes a uniform pseudo-random choice, and then executes that case. It returns the index of the chosen case and, if that case was a receive operation, the value received and a boolean indicating whether the value corresponds to a send on the channel (as opposed to a zero value received because the channel is closed).

func Select(cases []SelectCase) (chosen int, recv Value, recvOK bool)

type ChanDir

ChanDir represents a channel type's direction.

type ChanDir int
const (
        RecvDir ChanDir             = 1 << iota // <-chan
        SendDir                                 // chan<-
        BothDir = RecvDir | SendDir             // chan
)

func (ChanDir) String

func (d ChanDir) String() string

type Kind

A Kind represents the specific kind of type that a Type represents. The zero Kind is not a valid kind.

type Kind uint
const (
        Invalid Kind = iota
        Bool
        Int
        Int8
        Int16
        Int32
        Int64
        Uint
        Uint8
        Uint16
        Uint32
        Uint64
        Uintptr
        Float32
        Float64
        Complex64
        Complex128
        Array
        Chan
        Func
        Interface
        Map
        Ptr
        Slice
        String
        Struct
        UnsafePointer
)

func (Kind) String

func (k Kind) String() string

type Method

Method represents a single method.

type Method struct {
        // Name is the method name.
        // PkgPath is the package path that qualifies a lower case (unexported)
        // method name. It is empty for upper case (exported) method names.
        // The combination of PkgPath and Name uniquely identifies a method
        // in a method set.
        // See https://golang.org/ref/spec#Uniqueness_of_identifiers
        Name    string
        PkgPath string

        Type  Type  // method type
        Func  Value // func with receiver as first argument
        Index int   // index for Type.Method
}

type SelectCase

A SelectCase describes a single case in a select operation. The kind of case depends on Dir, the communication direction.

If Dir is SelectDefault, the case represents a default case. Chan and Send must be zero Values.

If Dir is SelectSend, the case represents a send operation. Normally Chan's underlying value must be a channel, and Send's underlying value must be assignable to the channel's element type. As a special case, if Chan is a zero Value, then the case is ignored, and the field Send will also be ignored and may be either zero or non-zero.

If Dir is SelectRecv, the case represents a receive operation. Normally Chan's underlying value must be a channel and Send must be a zero Value. If Chan is a zero Value, then the case is ignored, but Send must still be a zero Value. When a receive operation is selected, the received Value is returned by Select.

type SelectCase struct {
        Dir  SelectDir // direction of case
        Chan Value     // channel to use (for send or receive)
        Send Value     // value to send (for send)
}

type SelectDir

A SelectDir describes the communication direction of a select case.

type SelectDir int
const (
        SelectSend    SelectDir // case Chan <- Send
        SelectRecv              // case <-Chan:
        SelectDefault           // default
)

type SliceHeader

SliceHeader is the runtime representation of a slice. It cannot be used safely or portably and its representation may change in a later release. Moreover, the Data field is not sufficient to guarantee the data it references will not be garbage collected, so programs must keep a separate, correctly typed pointer to the underlying data.

type SliceHeader struct {
        Data uintptr
        Len  int
        Cap  int
}

type StringHeader

StringHeader is the runtime representation of a string. It cannot be used safely or portably and its representation may change in a later release. Moreover, the Data field is not sufficient to guarantee the data it references will not be garbage collected, so programs must keep a separate, correctly typed pointer to the underlying data.

type StringHeader struct {
        Data uintptr
        Len  int
}

type StructField

A StructField describes a single field in a struct.

type StructField struct {
        // Name is the field name.
        Name string
        // PkgPath is the package path that qualifies a lower case (unexported)
        // field name. It is empty for upper case (exported) field names.
        // See https://golang.org/ref/spec#Uniqueness_of_identifiers
        PkgPath string

        Type      Type      // field type
        Tag       StructTag // field tag string
        Offset    uintptr   // offset within struct, in bytes
        Index     []int     // index sequence for Type.FieldByIndex
        Anonymous bool      // is an embedded field
}

type StructTag

A StructTag is the tag string in a struct field.

By convention, tag strings are a concatenation of optionally space-separated key:"value" pairs. Each key is a non-empty string consisting of non-control characters other than space (U+0020 ' '), quote (U+0022 '"'), and colon (U+003A ':'). Each value is quoted using U+0022 '"' characters and Go string literal syntax.

type StructTag string

Example

blue gopher

func (StructTag) Get

Get returns the value associated with key in the tag string. If there is no such key in the tag, Get returns the empty string. If the tag does not have the conventional format, the value returned by Get is unspecified. To determine whether a tag is explicitly set to the empty string, use Lookup.

func (tag StructTag) Get(key string) string

func (StructTag) Lookup

Lookup returns the value associated with key in the tag string. If the key is present in the tag the value (which may be empty) is returned. Otherwise the returned value will be the empty string. The ok return value reports whether the value was explicitly set in the tag string. If the tag does not have the conventional format, the value returned by Lookup is unspecified.

func (tag StructTag) Lookup(key string) (value string, ok bool)

Example

field_0
(blank)
(not specified)

type Type

Type is the representation of a Go type.

Not all methods apply to all kinds of types. Restrictions, if any, are noted in the documentation for each method. Use the Kind method to find out the kind of type before calling kind-specific methods. Calling a method inappropriate to the kind of type causes a run-time panic.

type Type interface {

        // Align returns the alignment in bytes of a value of
        // this type when allocated in memory.
        Align() int

        // FieldAlign returns the alignment in bytes of a value of
        // this type when used as a field in a struct.
        FieldAlign() int

        // Method returns the i'th method in the type's method set.
        // It panics if i is not in the range [0, NumMethod()).
        //
        // For a non-interface type T or *T, the returned Method's Type and Func
        // fields describe a function whose first argument is the receiver.
        //
        // For an interface type, the returned Method's Type field gives the
        // method signature, without a receiver, and the Func field is nil.
        Method(int) Method

        // MethodByName returns the method with that name in the type's
        // method set and a boolean indicating if the method was found.
        //
        // For a non-interface type T or *T, the returned Method's Type and Func
        // fields describe a function whose first argument is the receiver.
        //
        // For an interface type, the returned Method's Type field gives the
        // method signature, without a receiver, and the Func field is nil.
        MethodByName(string) (Method, bool)

        // NumMethod returns the number of methods in the type's method set.
        NumMethod() int

        // Name returns the type's name within its package.
        // It returns an empty string for unnamed types.
        Name() string

        // PkgPath returns a named type's package path, that is, the import path
        // that uniquely identifies the package, such as "encoding/base64".
        // If the type was predeclared (string, error) or unnamed (*T, struct{}, []int),
        // the package path will be the empty string.
        PkgPath() string

        // Size returns the number of bytes needed to store
        // a value of the given type; it is analogous to unsafe.Sizeof.
        Size() uintptr

        // String returns a string representation of the type.
        // The string representation may use shortened package names
        // (e.g., base64 instead of "encoding/base64") and is not
        // guaranteed to be unique among types. To test for equality,
        // compare the Types directly.
        String() string

        // Kind returns the specific kind of this type.
        Kind() Kind

        // Implements reports whether the type implements the interface type u.
        Implements(u Type) bool

        // AssignableTo reports whether a value of the type is assignable to type u.
        AssignableTo(u Type) bool

        // ConvertibleTo reports whether a value of the type is convertible to type u.
        ConvertibleTo(u Type) bool

        // Comparable reports whether values of this type are comparable.
        Comparable() bool

        // Bits returns the size of the type in bits.
        // It panics if the type's Kind is not one of the
        // sized or unsized Int, Uint, Float, or Complex kinds.
        Bits() int

        // ChanDir returns a channel type's direction.
        // It panics if the type's Kind is not Chan.
        ChanDir() ChanDir

        // IsVariadic reports whether a function type's final input parameter
        // is a "..." parameter. If so, t.In(t.NumIn() - 1) returns the parameter's
        // implicit actual type []T.
        //
        // For concreteness, if t represents func(x int, y ... float64), then
        //
        //	t.NumIn() == 2
        //	t.In(0) is the reflect.Type for "int"
        //	t.In(1) is the reflect.Type for "[]float64"
        //	t.IsVariadic() == true
        //
        // IsVariadic panics if the type's Kind is not Func.
        IsVariadic() bool

        // Elem returns a type's element type.
        // It panics if the type's Kind is not Array, Chan, Map, Ptr, or Slice.
        Elem() Type

        // Field returns a struct type's i'th field.
        // It panics if the type's Kind is not Struct.
        // It panics if i is not in the range [0, NumField()).
        Field(i int) StructField

        // FieldByIndex returns the nested field corresponding
        // to the index sequence. It is equivalent to calling Field
        // successively for each index i.
        // It panics if the type's Kind is not Struct.
        FieldByIndex(index []int) StructField

        // FieldByName returns the struct field with the given name
        // and a boolean indicating if the field was found.
        FieldByName(name string) (StructField, bool)

        // FieldByNameFunc returns the first struct field with a name
        // that satisfies the match function and a boolean indicating if
        // the field was found.
        FieldByNameFunc(match func(string) bool) (StructField, bool)

        // In returns the type of a function type's i'th input parameter.
        // It panics if the type's Kind is not Func.
        // It panics if i is not in the range [0, NumIn()).
        In(i int) Type

        // Key returns a map type's key type.
        // It panics if the type's Kind is not Map.
        Key() Type

        // Len returns an array type's length.
        // It panics if the type's Kind is not Array.
        Len() int

        // NumField returns a struct type's field count.
        // It panics if the type's Kind is not Struct.
        NumField() int

        // NumIn returns a function type's input parameter count.
        // It panics if the type's Kind is not Func.
        NumIn() int

        // NumOut returns a function type's output parameter count.
        // It panics if the type's Kind is not Func.
        NumOut() int

        // Out returns the type of a function type's i'th output parameter.
        // It panics if the type's Kind is not Func.
        // It panics if i is not in the range [0, NumOut()).
        Out(i int) Type
        // contains filtered or unexported methods
}

func ArrayOf

ArrayOf returns the array type with the given count and element type. For example, if t represents int, ArrayOf(5, t) represents [5]int.

If the resulting type would be larger than the available address space, ArrayOf panics.

func ArrayOf(count int, elem Type) Type

func ChanOf

ChanOf returns the channel type with the given direction and element type. For example, if t represents int, ChanOf(RecvDir, t) represents <-chan int.

The gc runtime imposes a limit of 64 kB on channel element types. If t's size is equal to or exceeds this limit, ChanOf panics.

func ChanOf(dir ChanDir, t Type) Type

func FuncOf

FuncOf returns the function type with the given argument and result types. For example if k represents int and e represents string, FuncOf([]Type{k}, []Type{e}, false) represents func(int) string.

The variadic argument controls whether the function is variadic. FuncOf panics if the in[len(in)-1] does not represent a slice and variadic is true.

func FuncOf(in, out []Type, variadic bool) Type

func MapOf

MapOf returns the map type with the given key and element types. For example, if k represents int and e represents string, MapOf(k, e) represents map[int]string.

If the key type is not a valid map key type (that is, if it does not implement Go's == operator), MapOf panics.

func MapOf(key, elem Type) Type

func PtrTo

PtrTo returns the pointer type with element t. For example, if t represents type Foo, PtrTo(t) represents *Foo.

func PtrTo(t Type) Type

func SliceOf

SliceOf returns the slice type with element type t. For example, if t represents int, SliceOf(t) represents []int.

func SliceOf(t Type) Type

func StructOf

StructOf returns the struct type containing fields. The Offset and Index fields are ignored and computed as they would be by the compiler.

StructOf currently does not generate wrapper methods for embedded fields. This limitation may be lifted in a future version.

func StructOf(fields []StructField) Type

func TypeOf

TypeOf returns the reflection Type that represents the dynamic type of i. If i is a nil interface value, TypeOf returns nil.

func TypeOf(i interface{}) Type

Example

true

type Value

Value is the reflection interface to a Go value.

Not all methods apply to all kinds of values. Restrictions, if any, are noted in the documentation for each method. Use the Kind method to find out the kind of value before calling kind-specific methods. Calling a method inappropriate to the kind of type causes a run time panic.

The zero Value represents no value. Its IsValid method returns false, its Kind method returns Invalid, its String method returns "<invalid Value>", and all other methods panic. Most functions and methods never return an invalid value. If one does, its documentation states the conditions explicitly.

A Value can be used concurrently by multiple goroutines provided that the underlying Go value can be used concurrently for the equivalent direct operations.

Using == on two Values does not compare the underlying values they represent, but rather the contents of the Value structs. To compare two Values, compare the results of the Interface method.

type Value struct {
        // contains filtered or unexported fields
}

func Append

Append appends the values x to a slice s and returns the resulting slice. As in Go, each x's value must be assignable to the slice's element type.

func Append(s Value, x ...Value) Value

func AppendSlice

AppendSlice appends a slice t to a slice s and returns the resulting slice. The slices s and t must have the same element type.

func AppendSlice(s, t Value) Value

func Indirect

Indirect returns the value that v points to. If v is a nil pointer, Indirect returns a zero Value. If v is not a pointer, Indirect returns v.

func Indirect(v Value) Value

func MakeChan

MakeChan creates a new channel with the specified type and buffer size.

func MakeChan(typ Type, buffer int) Value

func MakeFunc

MakeFunc returns a new function of the given Type that wraps the function fn. When called, that new function does the following:

- converts its arguments to a slice of Values.
- runs results := fn(args).
- returns the results as a slice of Values, one per formal result.

The implementation fn can assume that the argument Value slice has the number and type of arguments given by typ. If typ describes a variadic function, the final Value is itself a slice representing the variadic arguments, as in the body of a variadic function. The result Value slice returned by fn must have the number and type of results given by typ.

The Value.Call method allows the caller to invoke a typed function in terms of Values; in contrast, MakeFunc allows the caller to implement a typed function in terms of Values.

The Examples section of the documentation includes an illustration of how to use MakeFunc to build a swap function for different types.

func MakeFunc(typ Type, fn func(args []Value) (results []Value)) Value

Example

1 0
3.14 2.72

func MakeMap

MakeMap creates a new map of the specified type.

func MakeMap(typ Type) Value

func MakeSlice

MakeSlice creates a new zero-initialized slice value for the specified slice type, length, and capacity.

func MakeSlice(typ Type, len, cap int) Value

func New

New returns a Value representing a pointer to a new zero value for the specified type. That is, the returned Value's Type is PtrTo(typ).

func New(typ Type) Value

func NewAt

NewAt returns a Value representing a pointer to a value of the specified type, using p as that pointer.

func NewAt(typ Type, p unsafe.Pointer) Value

func ValueOf

ValueOf returns a new Value initialized to the concrete value stored in the interface i. ValueOf(nil) returns the zero Value.

func ValueOf(i interface{}) Value

func Zero

Zero returns a Value representing the zero value for the specified type. The result is different from the zero value of the Value struct, which represents no value at all. For example, Zero(TypeOf(42)) returns a Value with Kind Int and value 0. The returned value is neither addressable nor settable.

func Zero(typ Type) Value

func (Value) Addr

Addr returns a pointer value representing the address of v. It panics if CanAddr() returns false. Addr is typically used to obtain a pointer to a struct field or slice element in order to call a method that requires a pointer receiver.

func (v Value) Addr() Value

func (Value) Bool

Bool returns v's underlying value. It panics if v's kind is not Bool.

func (v Value) Bool() bool

func (Value) Bytes

Bytes returns v's underlying value. It panics if v's underlying value is not a slice of bytes.

func (v Value) Bytes() []byte

func (Value) Call

Call calls the function v with the input arguments in. For example, if len(in) == 3, v.Call(in) represents the Go call v(in[0], in[1], in[2]). Call panics if v's Kind is not Func. It returns the output results as Values. As in Go, each input argument must be assignable to the type of the function's corresponding input parameter. If v is a variadic function, Call creates the variadic slice parameter itself, copying in the corresponding values.

func (v Value) Call(in []Value) []Value

func (Value) CallSlice

CallSlice calls the variadic function v with the input arguments in, assigning the slice in[len(in)-1] to v's final variadic argument. For example, if len(in) == 3, v.CallSlice(in) represents the Go call v(in[0], in[1], in[2]...). CallSlice panics if v's Kind is not Func or if v is not variadic. It returns the output results as Values. As in Go, each input argument must be assignable to the type of the function's corresponding input parameter.

func (v Value) CallSlice(in []Value) []Value

func (Value) CanAddr

CanAddr reports whether the value's address can be obtained with Addr. Such values are called addressable. A value is addressable if it is an element of a slice, an element of an addressable array, a field of an addressable struct, or the result of dereferencing a pointer. If CanAddr returns false, calling Addr will panic.

func (v Value) CanAddr() bool

func (Value) CanInterface

CanInterface reports whether Interface can be used without panicking.

func (v Value) CanInterface() bool

func (Value) CanSet

CanSet reports whether the value of v can be changed. A Value can be changed only if it is addressable and was not obtained by the use of unexported struct fields. If CanSet returns false, calling Set or any type-specific setter (e.g., SetBool, SetInt) will panic.

func (v Value) CanSet() bool

func (Value) Cap

Cap returns v's capacity. It panics if v's Kind is not Array, Chan, or Slice.

func (v Value) Cap() int

func (Value) Close

Close closes the channel v. It panics if v's Kind is not Chan.

func (v Value) Close()

func (Value) Complex

Complex returns v's underlying value, as a complex128. It panics if v's Kind is not Complex64 or Complex128

func (v Value) Complex() complex128

func (Value) Convert

Convert returns the value v converted to type t. If the usual Go conversion rules do not allow conversion of the value v to type t, Convert panics.

func (v Value) Convert(t Type) Value

func (Value) Elem

Elem returns the value that the interface v contains or that the pointer v points to. It panics if v's Kind is not Interface or Ptr. It returns the zero Value if v is nil.

func (v Value) Elem() Value

func (Value) Field

Field returns the i'th field of the struct v. It panics if v's Kind is not Struct or i is out of range.

func (v Value) Field(i int) Value

func (Value) FieldByIndex

FieldByIndex returns the nested field corresponding to index. It panics if v's Kind is not struct.

func (v Value) FieldByIndex(index []int) Value

func (Value) FieldByName

FieldByName returns the struct field with the given name. It returns the zero Value if no field was found. It panics if v's Kind is not struct.

func (v Value) FieldByName(name string) Value

func (Value) FieldByNameFunc

FieldByNameFunc returns the struct field with a name that satisfies the match function. It panics if v's Kind is not struct. It returns the zero Value if no field was found.

func (v Value) FieldByNameFunc(match func(string) bool) Value

func (Value) Float

Float returns v's underlying value, as a float64. It panics if v's Kind is not Float32 or Float64

func (v Value) Float() float64

func (Value) Index

Index returns v's i'th element. It panics if v's Kind is not Array, Slice, or String or i is out of range.

func (v Value) Index(i int) Value

func (Value) Int

Int returns v's underlying value, as an int64. It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64.

func (v Value) Int() int64

func (Value) Interface

Interface returns v's current value as an interface{}. It is equivalent to:

var i interface{} = (v's underlying value)

It panics if the Value was obtained by accessing unexported struct fields.

func (v Value) Interface() (i interface{})

func (Value) InterfaceData

InterfaceData returns the interface v's value as a uintptr pair. It panics if v's Kind is not Interface.

func (v Value) InterfaceData() [2]uintptr

func (Value) IsNil

IsNil reports whether its argument v is nil. The argument must be a chan, func, interface, map, pointer, or slice value; if it is not, IsNil panics. Note that IsNil is not always equivalent to a regular comparison with nil in Go. For example, if v was created by calling ValueOf with an uninitialized interface variable i, i==nil will be true but v.IsNil will panic as v will be the zero Value.

func (v Value) IsNil() bool

func (Value) IsValid

IsValid reports whether v represents a value. It returns false if v is the zero Value. If IsValid returns false, all other methods except String panic. Most functions and methods never return an invalid value. If one does, its documentation states the conditions explicitly.

func (v Value) IsValid() bool

func (Value) Kind

Kind returns v's Kind. If v is the zero Value (IsValid returns false), Kind returns Invalid.

func (v Value) Kind() Kind

func (Value) Len

Len returns v's length. It panics if v's Kind is not Array, Chan, Map, Slice, or String.

func (v Value) Len() int

func (Value) MapIndex

MapIndex returns the value associated with key in the map v. It panics if v's Kind is not Map. It returns the zero Value if key is not found in the map or if v represents a nil map. As in Go, the key's value must be assignable to the map's key type.

func (v Value) MapIndex(key Value) Value

func (Value) MapKeys

MapKeys returns a slice containing all the keys present in the map, in unspecified order. It panics if v's Kind is not Map. It returns an empty slice if v represents a nil map.

func (v Value) MapKeys() []Value

func (Value) Method

Method returns a function value corresponding to v's i'th method. The arguments to a Call on the returned function should not include a receiver; the returned function will always use v as the receiver. Method panics if i is out of range or if v is a nil interface value.

func (v Value) Method(i int) Value

func (Value) MethodByName

MethodByName returns a function value corresponding to the method of v with the given name. The arguments to a Call on the returned function should not include a receiver; the returned function will always use v as the receiver. It returns the zero Value if no method was found.

func (v Value) MethodByName(name string) Value

func (Value) NumField

NumField returns the number of fields in the struct v. It panics if v's Kind is not Struct.

func (v Value) NumField() int

func (Value) NumMethod

NumMethod returns the number of methods in the value's method set.

func (v Value) NumMethod() int

func (Value) OverflowComplex

OverflowComplex reports whether the complex128 x cannot be represented by v's type. It panics if v's Kind is not Complex64 or Complex128.

func (v Value) OverflowComplex(x complex128) bool

func (Value) OverflowFloat

OverflowFloat reports whether the float64 x cannot be represented by v's type. It panics if v's Kind is not Float32 or Float64.

func (v Value) OverflowFloat(x float64) bool

func (Value) OverflowInt

OverflowInt reports whether the int64 x cannot be represented by v's type. It panics if v's Kind is not Int, Int8, int16, Int32, or Int64.

func (v Value) OverflowInt(x int64) bool

func (Value) OverflowUint

OverflowUint reports whether the uint64 x cannot be represented by v's type. It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.

func (v Value) OverflowUint(x uint64) bool

func (Value) Pointer

Pointer returns v's value as a uintptr. It returns uintptr instead of unsafe.Pointer so that code using reflect cannot obtain unsafe.Pointers without importing the unsafe package explicitly. It panics if v's Kind is not Chan, Func, Map, Ptr, Slice, or UnsafePointer.

If v's Kind is Func, the returned pointer is an underlying code pointer, but not necessarily enough to identify a single function uniquely. The only guarantee is that the result is zero if and only if v is a nil func Value.

If v's Kind is Slice, the returned pointer is to the first element of the slice. If the slice is nil the returned value is 0. If the slice is empty but non-nil the return value is non-zero.

func (v Value) Pointer() uintptr

func (Value) Recv

Recv receives and returns a value from the channel v. It panics if v's Kind is not Chan. The receive blocks until a value is ready. The boolean value ok is true if the value x corresponds to a send on the channel, false if it is a zero value received because the channel is closed.

func (v Value) Recv() (x Value, ok bool)

func (Value) Send

Send sends x on the channel v. It panics if v's kind is not Chan or if x's type is not the same type as v's element type. As in Go, x's value must be assignable to the channel's element type.

func (v Value) Send(x Value)

func (Value) Set

Set assigns x to the value v. It panics if CanSet returns false. As in Go, x's value must be assignable to v's type.

func (v Value) Set(x Value)

func (Value) SetBool

SetBool sets v's underlying value. It panics if v's Kind is not Bool or if CanSet() is false.

func (v Value) SetBool(x bool)

func (Value) SetBytes

SetBytes sets v's underlying value. It panics if v's underlying value is not a slice of bytes.

func (v Value) SetBytes(x []byte)

func (Value) SetCap

SetCap sets v's capacity to n. It panics if v's Kind is not Slice or if n is smaller than the length or greater than the capacity of the slice.

func (v Value) SetCap(n int)

func (Value) SetComplex

SetComplex sets v's underlying value to x. It panics if v's Kind is not Complex64 or Complex128, or if CanSet() is false.

func (v Value) SetComplex(x complex128)

func (Value) SetFloat

SetFloat sets v's underlying value to x. It panics if v's Kind is not Float32 or Float64, or if CanSet() is false.

func (v Value) SetFloat(x float64)

func (Value) SetInt

SetInt sets v's underlying value to x. It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64, or if CanSet() is false.

func (v Value) SetInt(x int64)

func (Value) SetLen

SetLen sets v's length to n. It panics if v's Kind is not Slice or if n is negative or greater than the capacity of the slice.

func (v Value) SetLen(n int)

func (Value) SetMapIndex

SetMapIndex sets the value associated with key in the map v to val. It panics if v's Kind is not Map. If val is the zero Value, SetMapIndex deletes the key from the map. Otherwise if v holds a nil map, SetMapIndex will panic. As in Go, key's value must be assignable to the map's key type, and val's value must be assignable to the map's value type.

func (v Value) SetMapIndex(key, val Value)

func (Value) SetPointer

SetPointer sets the unsafe.Pointer value v to x. It panics if v's Kind is not UnsafePointer.

func (v Value) SetPointer(x unsafe.Pointer)

func (Value) SetString

SetString sets v's underlying value to x. It panics if v's Kind is not String or if CanSet() is false.

func (v Value) SetString(x string)

func (Value) SetUint

SetUint sets v's underlying value to x. It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64, or if CanSet() is false.

func (v Value) SetUint(x uint64)

func (Value) Slice

Slice returns v[i:j]. It panics if v's Kind is not Array, Slice or String, or if v is an unaddressable array, or if the indexes are out of bounds.

func (v Value) Slice(i, j int) Value

func (Value) Slice3

Slice3 is the 3-index form of the slice operation: it returns v[i:j:k]. It panics if v's Kind is not Array or Slice, or if v is an unaddressable array, or if the indexes are out of bounds.

func (v Value) Slice3(i, j, k int) Value

func (Value) String

String returns the string v's underlying value, as a string. String is a special case because of Go's String method convention. Unlike the other getters, it does not panic if v's Kind is not String. Instead, it returns a string of the form "<T value>" where T is v's type. The fmt package treats Values specially. It does not call their String method implicitly but instead prints the concrete values they hold.

func (v Value) String() string

func (Value) TryRecv

TryRecv attempts to receive a value from the channel v but will not block. It panics if v's Kind is not Chan. If the receive delivers a value, x is the transferred value and ok is true. If the receive cannot finish without blocking, x is the zero Value and ok is false. If the channel is closed, x is the zero value for the channel's element type and ok is false.

func (v Value) TryRecv() (x Value, ok bool)

func (Value) TrySend

TrySend attempts to send x on the channel v but will not block. It panics if v's Kind is not Chan. It reports whether the value was sent. As in Go, x's value must be assignable to the channel's element type.

func (v Value) TrySend(x Value) bool

func (Value) Type

Type returns v's type.

func (v Value) Type() Type

func (Value) Uint

Uint returns v's underlying value, as a uint64. It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.

func (v Value) Uint() uint64

func (Value) UnsafeAddr

UnsafeAddr returns a pointer to v's data. It is for advanced clients that also import the "unsafe" package. It panics if v is not addressable.

func (v Value) UnsafeAddr() uintptr

type ValueError

A ValueError occurs when a Value method is invoked on a Value that does not support it. Such cases are documented in the description of each method.

type ValueError struct {
        Method string
        Kind   Kind
}

func (*ValueError) Error

func (e *ValueError) Error() string

Bugs