reflect

package
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 Go to latest Published: Jun 9, 2011 License: BSD-3-Clause Imports: 5 Imported by: 0

Documentation

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.

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

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 members of arrays, slices, and fields of structs. It correctly handles recursive types.

Types

type ChanDir 

type ChanDir int

ChanDir represents a channel type's direction. 

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

func (ChanDir) String 

func (d ChanDir) String() string

type Kind 

type Kind uint8

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 {
	PkgPath string // empty for uppercase Name
	Name    string
	Type    Type
	Func    Value
}

Method represents a single method.

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.

type StringHeader 

type StringHeader struct {
	Data uintptr
	Len  int
}

StringHeader is the runtime representation of a string. It cannot be used safely or portably.

type StructField 

type StructField struct {
	PkgPath   string // empty for uppercase Name
	Name      string
	Type      Type
	Tag       string
	Offset    uintptr
	Index     []int
	Anonymous bool
}

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

	// 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 the type's package path.
	// The package path is a full package import path like "container/vector".
	// PkgPath returns an empty string for unnamed types.
	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., vector instead of "container/vector") 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

	// 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 ... float), then
	//
	//	t.NumIn() == 2
	//	t.In(0) is the reflect.Type for "int"
	//	t.In(1) is the reflect.Type for "[]float"
	//	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 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 TypeOf 

func TypeOf(i interface{}) Type

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

type Value 

type Value struct {
	Internal       interface{}
	InternalMethod int
}

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.

The fields of Value are exported so that clients can copy and pass Values around, but they should not be edited or inspected directly. A future language change may make it possible not to export these fields while still keeping Values usable as values.

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 nil 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 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 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 a 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.

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) 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) 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 an 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 or Slice 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() interface{}

Interface returns v's value as an interface{}. If v is a method obtained by invoking Value.Method (as opposed to Type.Method), Interface cannot return an interface value, so it panics.

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, or Slice.

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.

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) 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.

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) 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.

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(beg, end int) Value

Slice returns a slice of v. It panics if v's Kind is not Array or Slice.

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) String 

func (e *ValueError) String() string

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