Run Format

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: http://golang.org/doc/articles/laws_of_reflection.html

Index ▾

Constants
func Copy(dst, src Value) int
func DeepEqual(a1, a2 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
type Type
    func ChanOf(dir ChanDir, t Type) Type
    func MapOf(key, elem Type) Type
    func PtrTo(t Type) Type
    func SliceOf(t Type) 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

Examples

MakeFunc
StructTag

Package files

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

Constants

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

func Copy

func Copy(dst, src Value) int

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 DeepEqual

func DeepEqual(a1, a2 interface{}) bool

DeepEqual tests for deep equality. It uses normal == equality where possible but will scan elements of arrays, slices, maps, and fields of structs. In maps, keys are compared with == but elements use deep equality. DeepEqual correctly handles recursive types. Functions are equal only if they are both nil. An empty slice is not equal to a nil slice.

func Select

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

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).

type ChanDir

type ChanDir int

ChanDir represents a channel type's direction.

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

func (ChanDir) String

func (d ChanDir) String() string

type Kind

type Kind uint

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

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

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 http://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
}

Method represents a single method.

type SelectCase

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

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 SelectDir

type SelectDir int

A SelectDir describes the communication direction of a select case.

type SliceHeader

type SliceHeader struct {
        Data uintptr
        Len  int
        Cap  int
}

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 StringHeader

type StringHeader struct {
        Data uintptr
        Len  int
}

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 StructField

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

A StructField describes a single field in a struct.

type StructTag

type StructTag string

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.

Example

blue gopher

func (StructTag) Get

func (tag StructTag) Get(key string) string

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.

type Type

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 returns true if the type implements the interface type u.
        Implements(u Type) bool

        // AssignableTo returns true if a value of the type is assignable to type u.
        AssignableTo(u Type) bool

        // ConvertibleTo returns true if a value of the type is convertible to type u.
        ConvertibleTo(u Type) 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 returns true if 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
}

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.

func ChanOf

func ChanOf(dir ChanDir, t Type) Type

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 MapOf

func MapOf(key, elem Type) Type

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 PtrTo

func PtrTo(t Type) Type

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

func SliceOf

func SliceOf(t Type) Type

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

func TypeOf

func TypeOf(i interface{}) Type

TypeOf returns the reflection Type of the value in the interface{}. TypeOf(nil) returns nil.

type Value

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

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.

func Append

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

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 AppendSlice

func AppendSlice(s, t Value) Value

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 Indirect

func Indirect(v Value) Value

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 MakeChan

func MakeChan(typ Type, buffer int) Value

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

func MakeFunc

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

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.

Example

1 0
3.14 2.72

func MakeMap

func MakeMap(typ Type) Value

MakeMap creates a new map of the specified type.

func MakeSlice

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

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

func New

func New(typ Type) Value

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(t).

func NewAt

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

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

func ValueOf

func ValueOf(i interface{}) Value

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

func Zero

func Zero(typ Type) Value

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 (Value) Addr

func (v Value) Addr() Value

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 (Value) Bool

func (v Value) Bool() bool

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

func (Value) Bytes

func (v Value) Bytes() []byte

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

func (Value) Call

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

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 (Value) CallSlice

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

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.Call(in) represents the Go call v(in[0], in[1], in[2]...). Call 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 (Value) CanAddr

func (v Value) CanAddr() bool

CanAddr returns true if 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 (Value) CanInterface

func (v Value) CanInterface() bool

CanInterface returns true if Interface can be used without panicking.

func (Value) CanSet

func (v Value) CanSet() bool

CanSet returns true if 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, SetInt64) will panic.

func (Value) Cap

func (v Value) Cap() int

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

func (Value) Close

func (v Value) Close()

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

func (Value) Complex

func (v Value) Complex() complex128

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

func (Value) Convert

func (v Value) Convert(t Type) Value

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 (Value) Elem

func (v Value) Elem() Value

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 (Value) Field

func (v Value) Field(i int) Value

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 (Value) FieldByIndex

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

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

func (Value) FieldByName

func (v Value) FieldByName(name string) Value

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 (Value) FieldByNameFunc

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

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 (Value) Float

func (v Value) Float() float64

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

func (Value) Index

func (v Value) Index(i int) Value

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 (Value) Int

func (v Value) Int() int64

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

func (Value) Interface

func (v Value) Interface() (i 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 (Value) InterfaceData

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

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

func (Value) IsNil

func (v Value) IsNil() bool

IsNil returns true if v is a nil value. It panics if v's Kind is not Chan, Func, Interface, Map, Ptr, or Slice.

func (Value) IsValid

func (v Value) IsValid() bool

IsValid returns true if 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 (Value) Kind

func (v Value) Kind() Kind

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

func (Value) Len

func (v Value) Len() int

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

func (Value) MapIndex

func (v Value) MapIndex(key Value) Value

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 (Value) MapKeys

func (v Value) MapKeys() []Value

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 (Value) Method

func (v Value) Method(i int) Value

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 (Value) MethodByName

func (v Value) MethodByName(name string) Value

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 (Value) NumField

func (v Value) NumField() int

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

func (Value) NumMethod

func (v Value) NumMethod() int

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

func (Value) OverflowComplex

func (v Value) OverflowComplex(x complex128) bool

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

func (Value) OverflowFloat

func (v Value) OverflowFloat(x float64) bool

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

func (Value) OverflowInt

func (v Value) OverflowInt(x int64) bool

OverflowInt returns true if 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 (Value) OverflowUint

func (v Value) OverflowUint(x uint64) bool

OverflowUint returns true if 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 (Value) Pointer

func (v Value) Pointer() uintptr

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.

func (Value) Recv

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

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 (Value) Send

func (v Value) Send(x Value)

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 (Value) Set

func (v Value) Set(x Value)

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 (Value) SetBool

func (v Value) SetBool(x bool)

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

func (Value) SetBytes

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

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

func (Value) SetCap

func (v Value) SetCap(n int)

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 (Value) SetComplex

func (v Value) SetComplex(x complex128)

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 (Value) SetFloat

func (v Value) SetFloat(x float64)

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 (Value) SetInt

func (v Value) SetInt(x int64)

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 (Value) SetLen

func (v Value) SetLen(n int)

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 (Value) SetMapIndex

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

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. 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 (Value) SetPointer

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

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

func (Value) SetString

func (v Value) SetString(x string)

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

func (Value) SetUint

func (v Value) SetUint(x uint64)

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 (Value) Slice

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

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 (Value) Slice3

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

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 (Value) String

func (v Value) String() 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.

func (Value) TryRecv

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

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 cannot finish without blocking, x is the zero Value. The boolean 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 (Value) TrySend

func (v Value) TrySend(x Value) bool

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

func (Value) Type

func (v Value) Type() Type

Type returns v's type.

func (Value) Uint

func (v Value) Uint() uint64

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 (Value) UnsafeAddr

func (v Value) UnsafeAddr() uintptr

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.

type ValueError

type ValueError struct {
        Method string
        Kind   Kind
}

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.

func (*ValueError) Error

func (e *ValueError) Error() string