reflect

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 Go to latest Published: Jan 3, 2023 License: MIT Imports: 4 Imported by: 0

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Constants

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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.

As a special case, src can have kind String if the element type of dst is kind Uint8.

Types

type MapIter 

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

A MapIter is an iterator for ranging over a map. See Value.MapRange.

func (*MapIter) Key 

func (it *MapIter) Key() Value

Key returns the key of the iterator's current map entry.

func (*MapIter) Next 

func (it *MapIter) Next() bool

Next advances the map iterator and reports whether there is another entry. It returns false when the iterator is exhausted; subsequent calls to Key, Value, or Next will panic.

func (*MapIter) Value 

func (it *MapIter) Value() Value

Value returns the value of the iterator's current map entry.

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. 

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

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 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.

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

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 MakeMap 

func MakeMap(typ Type) Value

MakeMap creates a new map with the specified type.

func MakeMapWithSize 

func MakeMapWithSize(typ Type, n int) Value

MakeMapWithSize creates a new map with the specified type and initial space for approximately n elements.

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(typ).

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 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). Select supports a maximum of 65536 cases.

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.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 (Value) CanAddr 

func (v Value) CanAddr() bool

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 (Value) CanInterface 

func (v Value) CanInterface() bool

CanInterface reports whether Interface can be used without panicking.

func (Value) CanSet 

func (v Value) CanSet() bool

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 (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 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 (Value) IsValid 

func (v Value) IsValid() bool

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 (Value) IsZero 

func (v Value) IsZero() bool

IsZero reports whether v is the zero value for its type. It panics if the argument is invalid.

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) MapRange 

func (v Value) MapRange() *MapIter

MapRange returns a range iterator for a map. It panics if v's Kind is not Map.

Call Next to advance the iterator, and Key/Value to access each entry. Next returns false when the iterator is exhausted. MapRange follows the same iteration semantics as a range statement.

Example: 

iter := reflect.ValueOf(m).MapRange()
for iter.Next() {
	k := iter.Key()
	v := iter.Value()
	...
}

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 exported methods in the value's method set.

func (Value) OverflowComplex 

func (v Value) OverflowComplex(x complex128) bool

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 (Value) OverflowFloat 

func (v Value) OverflowFloat(x float64) bool

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 (Value) OverflowInt 

func (v Value) OverflowInt(x int64) bool

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 (Value) OverflowUint 

func (v Value) OverflowUint(x uint64) bool

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 (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.

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 (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, elem Value)

SetMapIndex sets the element associated with key in the map v to elem. It panics if v's Kind is not Map. If elem 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 elem must be assignable to the map's key type, and elem's value must be assignable to the map's elem 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. The fmt package treats Values specially. It does not call their String method implicitly but instead prints the concrete values they hold.

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 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 (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 reports whether the value was sent. 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

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