1 // Copyright 2009 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
14 const ptrSize = unsafe.Sizeof((*byte)(nil))
15 const cannotSet = "cannot set value obtained from unexported struct field"
17 // TODO: This will have to go away when
18 // the new gc goes in.
19 func memmove(adst, asrc unsafe.Pointer, n uintptr) {
23 case src < dst && src+n > dst:
25 // careful: i is unsigned
28 *(*byte)(unsafe.Pointer(dst + i)) = *(*byte)(unsafe.Pointer(src + i))
30 case (n|src|dst)&(ptrSize-1) != 0:
32 for i := uintptr(0); i < n; i++ {
33 *(*byte)(unsafe.Pointer(dst + i)) = *(*byte)(unsafe.Pointer(src + i))
37 for i := uintptr(0); i < n; i += ptrSize {
38 *(*uintptr)(unsafe.Pointer(dst + i)) = *(*uintptr)(unsafe.Pointer(src + i))
43 // Value is the reflection interface to a Go value.
45 // Not all methods apply to all kinds of values. Restrictions,
46 // if any, are noted in the documentation for each method.
47 // Use the Kind method to find out the kind of value before
48 // calling kind-specific methods. Calling a method
49 // inappropriate to the kind of type causes a run time panic.
51 // The zero Value represents no value.
52 // Its IsValid method returns false, its Kind method returns Invalid,
53 // its String method returns "<invalid Value>", and all other methods panic.
54 // Most functions and methods never return an invalid value.
55 // If one does, its documentation states the conditions explicitly.
57 // The fields of Value are exported so that clients can copy and
58 // pass Values around, but they should not be edited or inspected
59 // directly. A future language change may make it possible not to
60 // export these fields while still keeping Values usable as values.
66 // A ValueError occurs when a Value method is invoked on
67 // a Value that does not support it. Such cases are documented
68 // in the description of each method.
69 type ValueError struct {
74 func (e *ValueError) String() string {
76 return "reflect: call of " + e.Method + " on zero Value"
78 return "reflect: call of " + e.Method + " on " + e.Kind.String() + " Value"
81 // methodName returns the name of the calling method,
82 // assumed to be two stack frames above.
83 func methodName() string {
84 pc, _, _, _ := runtime.Caller(2)
85 f := runtime.FuncForPC(pc)
87 return "unknown method"
92 // An iword is the word that would be stored in an
93 // interface to represent a given value v. Specifically, if v is
94 // bigger than a pointer, its word is a pointer to v's data.
95 // Otherwise, its word is a zero uintptr with the data stored
96 // in the leading bytes.
99 func loadIword(p unsafe.Pointer, size uintptr) iword {
100 // Run the copy ourselves instead of calling memmove
101 // to avoid moving v to the heap.
105 panic("reflect: internal error: loadIword of " + strconv.Itoa(int(size)) + "-byte value")
108 *(*uint8)(unsafe.Pointer(&w)) = *(*uint8)(p)
110 *(*uint16)(unsafe.Pointer(&w)) = *(*uint16)(p)
112 *(*[3]byte)(unsafe.Pointer(&w)) = *(*[3]byte)(p)
114 *(*uint32)(unsafe.Pointer(&w)) = *(*uint32)(p)
116 *(*[5]byte)(unsafe.Pointer(&w)) = *(*[5]byte)(p)
118 *(*[6]byte)(unsafe.Pointer(&w)) = *(*[6]byte)(p)
120 *(*[7]byte)(unsafe.Pointer(&w)) = *(*[7]byte)(p)
122 *(*uint64)(unsafe.Pointer(&w)) = *(*uint64)(p)
127 func storeIword(p unsafe.Pointer, w iword, size uintptr) {
128 // Run the copy ourselves instead of calling memmove
129 // to avoid moving v to the heap.
132 panic("reflect: internal error: storeIword of " + strconv.Itoa(int(size)) + "-byte value")
135 *(*uint8)(p) = *(*uint8)(unsafe.Pointer(&w))
137 *(*uint16)(p) = *(*uint16)(unsafe.Pointer(&w))
139 *(*[3]byte)(p) = *(*[3]byte)(unsafe.Pointer(&w))
141 *(*uint32)(p) = *(*uint32)(unsafe.Pointer(&w))
143 *(*[5]byte)(p) = *(*[5]byte)(unsafe.Pointer(&w))
145 *(*[6]byte)(p) = *(*[6]byte)(unsafe.Pointer(&w))
147 *(*[7]byte)(p) = *(*[7]byte)(unsafe.Pointer(&w))
149 *(*uint64)(p) = *(*uint64)(unsafe.Pointer(&w))
153 // emptyInterface is the header for an interface{} value.
154 type emptyInterface struct {
159 // nonEmptyInterface is the header for a interface value with methods.
160 type nonEmptyInterface struct {
161 // see ../runtime/iface.c:/Itab
163 typ *runtime.Type // dynamic concrete type
164 fun [100000]unsafe.Pointer // method table
169 // Regarding the implementation of Value:
171 // The Internal interface is a true interface value in the Go sense,
172 // but it also serves as a (type, address) pair in which one cannot
173 // be changed separately from the other. That is, it serves as a way
174 // to prevent unsafe mutations of the Internal state even though
175 // we cannot (yet?) hide the field while preserving the ability for
176 // clients to make copies of Values.
178 // The internal method converts a Value into the expanded internalValue struct.
179 // If we could avoid exporting fields we'd probably make internalValue the
180 // definition of Value.
182 // If a Value is addressable (CanAddr returns true), then the Internal
183 // interface value holds a pointer to the actual field data, and Set stores
184 // through that pointer. If a Value is not addressable (CanAddr returns false),
185 // then the Internal interface value holds the actual value.
187 // In addition to whether a value is addressable, we track whether it was
188 // obtained by using an unexported struct field. Such values are allowed
189 // to be read, mainly to make fmt.Print more useful, but they are not
190 // allowed to be written. We call such values read-only.
192 // A Value can be set (via the Set, SetUint, etc. methods) only if it is both
193 // addressable and not read-only.
195 // The two permission bits - addressable and read-only - are stored in
196 // the bottom two bits of the type pointer in the interface value.
198 // ordinary value: Internal = value
199 // addressable value: Internal = value, Internal.typ |= flagAddr
200 // read-only value: Internal = value, Internal.typ |= flagRO
201 // addressable, read-only value: Internal = value, Internal.typ |= flagAddr | flagRO
203 // It is important that the read-only values have the extra bit set
204 // (as opposed to using the bit to mean writable), because client code
205 // can grab the interface field and try to use it. Having the extra bit
206 // set makes the type pointer compare not equal to any real type,
207 // so that a client cannot, say, write through v.Internal.(*int).
208 // The runtime routines that access interface types reject types with
211 // If a Value fv = v.Method(i), then fv = v with the InternalMethod
212 // field set to i+1. Methods are never addressable.
214 // All in all, this is a lot of effort just to avoid making this new API
215 // depend on a language change we'll probably do anyway, but
216 // it's helpful to keep the two separate, and much of the logic is
217 // necessary to implement the Interface method anyway.
220 flagAddr uint32 = 1 << iota // holds address of value
226 // An internalValue is the unpacked form of a Value.
227 // The zero Value unpacks to a zero internalValue
228 type internalValue struct {
229 typ *commonType // type of value
230 kind Kind // kind of value
239 func (v Value) internal() internalValue {
241 eface := *(*emptyInterface)(unsafe.Pointer(&v.Internal))
242 p := uintptr(unsafe.Pointer(eface.typ))
243 iv.typ = toCommonType((*runtime.Type)(unsafe.Pointer(p &^ reflectFlags)))
247 iv.flag = uint32(p & reflectFlags)
249 if iv.flag&flagAddr != 0 {
250 iv.addr = unsafe.Pointer(uintptr(iv.word))
251 iv.typ = iv.typ.Elem().common()
252 if Kind(iv.typ.kind) == Ptr || Kind(iv.typ.kind) == UnsafePointer {
253 iv.word = loadIword(iv.addr, iv.typ.size)
256 if Kind(iv.typ.kind) != Ptr && Kind(iv.typ.kind) != UnsafePointer {
257 iv.addr = unsafe.Pointer(uintptr(iv.word))
260 iv.kind = iv.typ.Kind()
262 // Is this a method? If so, iv describes the receiver.
263 // Rewrite to describe the method function.
264 if v.InternalMethod != 0 {
265 // If this Value is a method value (x.Method(i) for some Value x)
266 // then we will invoke it using the interface form of the method,
267 // which always passes the receiver as a single word.
268 // Record that information.
269 i := v.InternalMethod - 1
270 if iv.kind == Interface {
271 it := (*interfaceType)(unsafe.Pointer(iv.typ))
272 if i < 0 || i >= len(it.methods) {
273 panic("reflect: broken Value")
276 if m.pkgPath != nil {
279 iv.typ = toCommonType(m.typ)
280 iface := (*nonEmptyInterface)(iv.addr)
281 if iface.itab == nil {
285 iv.word = iword(uintptr(iface.itab.fun[i]))
289 ut := iv.typ.uncommon()
290 if ut == nil || i < 0 || i >= len(ut.methods) {
291 panic("reflect: broken Value")
294 if m.pkgPath != nil {
297 iv.typ = toCommonType(m.mtyp)
299 iv.word = iword(uintptr(m.tfn))
304 iv.word = iword(uintptr(unsafe.Pointer(p)))
309 iv.addr = unsafe.Pointer(uintptr(iv.word))
315 // packValue returns a Value with the given flag bits, type, and interface word.
316 func packValue(flag uint32, typ *runtime.Type, word iword) Value {
320 t := uintptr(unsafe.Pointer(typ))
322 eface := emptyInterface{(*runtime.Type)(unsafe.Pointer(t)), word}
323 return Value{Internal: *(*interface{})(unsafe.Pointer(&eface))}
326 // valueFromAddr returns a Value using the given type and address.
327 func valueFromAddr(flag uint32, typ Type, addr unsafe.Pointer) Value {
328 if flag&flagAddr != 0 {
329 // Addressable, so the internal value is
330 // an interface containing a pointer to the real value.
331 return packValue(flag, PtrTo(typ).runtimeType(), iword(uintptr(addr)))
335 if k := typ.Kind(); k == Ptr || k == UnsafePointer {
336 // In line, so the interface word is the actual value.
337 w = loadIword(addr, typ.Size())
339 // Not in line: the interface word is the address.
340 w = iword(uintptr(addr))
342 return packValue(flag, typ.runtimeType(), w)
345 // valueFromIword returns a Value using the given type and interface word.
346 func valueFromIword(flag uint32, typ Type, w iword) Value {
347 if flag&flagAddr != 0 {
348 panic("reflect: internal error: valueFromIword addressable")
350 return packValue(flag, typ.runtimeType(), w)
353 func (iv internalValue) mustBe(want Kind) {
355 panic(&ValueError{methodName(), iv.kind})
359 func (iv internalValue) mustBeExported() {
361 panic(&ValueError{methodName(), iv.kind})
363 if iv.flag&flagRO != 0 {
364 panic(methodName() + " using value obtained using unexported field")
368 func (iv internalValue) mustBeAssignable() {
370 panic(&ValueError{methodName(), iv.kind})
372 // Assignable if addressable and not read-only.
373 if iv.flag&flagRO != 0 {
374 panic(methodName() + " using value obtained using unexported field")
376 if iv.flag&flagAddr == 0 {
377 panic(methodName() + " using unaddressable value")
381 // Addr returns a pointer value representing the address of v.
382 // It panics if CanAddr() returns false.
383 // Addr is typically used to obtain a pointer to a struct field
384 // or slice element in order to call a method that requires a
386 func (v Value) Addr() Value {
388 if iv.flag&flagAddr == 0 {
389 panic("reflect.Value.Addr of unaddressable value")
391 return valueFromIword(iv.flag&flagRO, PtrTo(iv.typ.toType()), iword(uintptr(iv.addr)))
394 // Bool returns v's underlying value.
395 // It panics if v's kind is not Bool.
396 func (v Value) Bool() bool {
399 return *(*bool)(unsafe.Pointer(iv.addr))
402 // CanAddr returns true if the value's address can be obtained with Addr.
403 // Such values are called addressable. A value is addressable if it is
404 // an element of a slice, an element of an addressable array,
405 // a field of an addressable struct, or the result of dereferencing a pointer.
406 // If CanAddr returns false, calling Addr will panic.
407 func (v Value) CanAddr() bool {
409 return iv.flag&flagAddr != 0
412 // CanSet returns true if the value of v can be changed.
413 // A Value can be changed only if it is addressable and was not
414 // obtained by the use of unexported struct fields.
415 // If CanSet returns false, calling Set or any type-specific
416 // setter (e.g., SetBool, SetInt64) will panic.
417 func (v Value) CanSet() bool {
419 return iv.flag&(flagAddr|flagRO) == flagAddr
422 // Call calls the function v with the input arguments in.
423 // For example, if len(in) == 3, v.Call(in) represents the Go call v(in[0], in[1], in[2]).
424 // Call panics if v's Kind is not Func.
425 // It returns the output results as Values.
426 // As in Go, each input argument must be assignable to the
427 // type of the function's corresponding input parameter.
428 // If v is a variadic function, Call creates the variadic slice parameter
429 // itself, copying in the corresponding values.
430 func (v Value) Call(in []Value) []Value {
434 return iv.call("Call", in)
437 // CallSlice calls the variadic function v with the input arguments in,
438 // assigning the slice in[len(in)-1] to v's final variadic argument.
439 // For example, if len(in) == 3, v.Call(in) represents the Go call v(in[0], in[1], in[2]...).
440 // Call panics if v's Kind is not Func or if v is not variadic.
441 // It returns the output results as Values.
442 // As in Go, each input argument must be assignable to the
443 // type of the function's corresponding input parameter.
444 func (v Value) CallSlice(in []Value) []Value {
448 return iv.call("CallSlice", in)
451 func (iv internalValue) call(method string, in []Value) []Value {
454 panic("reflect.Value.Call: call of method on nil interface value")
456 panic("reflect.Value.Call: call of nil function")
459 isSlice := method == "CallSlice"
464 panic("reflect: CallSlice of non-variadic function")
467 panic("reflect: CallSlice with too few input arguments")
470 panic("reflect: CallSlice with too many input arguments")
477 panic("reflect: Call with too few input arguments")
479 if !t.IsVariadic() && len(in) > n {
480 panic("reflect: Call with too many input arguments")
483 for _, x := range in {
484 if x.Kind() == Invalid {
485 panic("reflect: " + method + " using zero Value argument")
488 for i := 0; i < n; i++ {
489 if xt, targ := in[i].Type(), t.In(i); !xt.AssignableTo(targ) {
490 panic("reflect: " + method + " using " + xt.String() + " as type " + targ.String())
493 if !isSlice && t.IsVariadic() {
494 // prepare slice for remaining values
496 slice := MakeSlice(t.In(n), m, m)
497 elem := t.In(n).Elem()
498 for i := 0; i < m; i++ {
500 if xt := x.Type(); !xt.AssignableTo(elem) {
501 panic("reflect: cannot use " + xt.String() + " as type " + elem.String() + " in " + method)
503 slice.Index(i).Set(x)
506 in = make([]Value, n+1)
512 if nin != t.NumIn() {
513 panic("reflect.Value.Call: wrong argument count")
520 params := make([]unsafe.Pointer, nin)
524 // Hard-wired first argument.
527 params[0] = unsafe.Pointer(p)
531 first_pointer := false
532 for i, v := range in {
535 targ := t.In(i).(*commonType)
536 siv = convertForAssignment("reflect.Value.Call", nil, targ, siv)
538 p := new(unsafe.Pointer)
539 *p = unsafe.Pointer(uintptr(siv.word))
540 params[off] = unsafe.Pointer(p)
542 params[off] = siv.addr
544 if i == 0 && Kind(targ.kind) != Ptr && !iv.method && isMethod(iv.typ) {
545 p := new(unsafe.Pointer)
547 params[off] = unsafe.Pointer(p)
553 ret := make([]Value, nout)
554 results := make([]unsafe.Pointer, nout)
555 for i := 0; i < nout; i++ {
557 results[i] = unsafe.Pointer(v.Pointer())
561 var pp *unsafe.Pointer
565 var pr *unsafe.Pointer
566 if len(results) > 0 {
570 call(t, *(*unsafe.Pointer)(iv.addr), iv.method, first_pointer, pp, pr)
575 // gccgo specific test to see if typ is a method. We can tell by
576 // looking at the string to see if there is a receiver. We need this
577 // because for gccgo all methods take pointer receivers.
578 func isMethod(t *commonType) bool {
579 if Kind(t.kind) != Func {
586 for i, c := range s {
592 } else if parens == 0 && c == ' ' && s[i + 1] != '(' && !sawRet {
600 // Cap returns v's capacity.
601 // It panics if v's Kind is not Array, Chan, or Slice.
602 func (v Value) Cap() int {
608 return int(chancap(*(*iword)(iv.addr)))
610 return (*SliceHeader)(iv.addr).Cap
612 panic(&ValueError{"reflect.Value.Cap", iv.kind})
615 // Close closes the channel v.
616 // It panics if v's Kind is not Chan.
617 func (v Value) Close() {
621 ch := *(*iword)(iv.addr)
625 // Complex returns v's underlying value, as a complex128.
626 // It panics if v's Kind is not Complex64 or Complex128
627 func (v Value) Complex() complex128 {
631 return complex128(*(*complex64)(iv.addr))
633 return *(*complex128)(iv.addr)
635 panic(&ValueError{"reflect.Value.Complex", iv.kind})
638 // Elem returns the value that the interface v contains
639 // or that the pointer v points to.
640 // It panics if v's Kind is not Interface or Ptr.
641 // It returns the zero Value if v is nil.
642 func (v Value) Elem() Value {
647 func (iv internalValue) Elem() Value {
650 // Empty interface and non-empty interface have different layouts.
651 // Convert to empty interface.
652 var eface emptyInterface
653 if iv.typ.NumMethod() == 0 {
654 eface = *(*emptyInterface)(iv.addr)
656 iface := (*nonEmptyInterface)(iv.addr)
657 if iface.itab != nil {
658 eface.typ = iface.itab.typ
660 eface.word = iface.word
662 if eface.typ == nil {
665 return valueFromIword(iv.flag&flagRO, toType(eface.typ), eface.word)
668 // The returned value's address is v's value.
672 return valueFromAddr(iv.flag&flagRO|flagAddr, iv.typ.Elem(), unsafe.Pointer(uintptr(iv.word)))
674 panic(&ValueError{"reflect.Value.Elem", iv.kind})
677 // Field returns the i'th field of the struct v.
678 // It panics if v's Kind is not Struct or i is out of range.
679 func (v Value) Field(i int) Value {
683 if i < 0 || i >= t.NumField() {
684 panic("reflect: Field index out of range")
688 // Inherit permission bits from v.
690 // Using an unexported field forces flagRO.
694 return valueFromValueOffset(flag, f.Type, iv, f.Offset)
697 // valueFromValueOffset returns a sub-value of outer
698 // (outer is an array or a struct) with the given flag and type
699 // starting at the given byte offset into outer.
700 func valueFromValueOffset(flag uint32, typ Type, outer internalValue, offset uintptr) Value {
701 if outer.addr != nil {
702 return valueFromAddr(flag, typ, unsafe.Pointer(uintptr(outer.addr)+offset))
705 // outer is so tiny it is in line.
706 // We have to use outer.word and derive
707 // the new word (it cannot possibly be bigger).
708 // In line, so not addressable.
709 if flag&flagAddr != 0 {
710 panic("reflect: internal error: misuse of valueFromValueOffset")
712 b := *(*[ptrSize]byte)(unsafe.Pointer(&outer.word))
713 for i := uintptr(0); i < typ.Size(); i++ {
716 for i := typ.Size(); i < ptrSize; i++ {
719 w := *(*iword)(unsafe.Pointer(&b))
720 return valueFromIword(flag, typ, w)
723 // FieldByIndex returns the nested field corresponding to index.
724 // It panics if v's Kind is not struct.
725 func (v Value) FieldByIndex(index []int) Value {
726 v.internal().mustBe(Struct)
727 for i, x := range index {
729 if v.Kind() == Ptr && v.Elem().Kind() == Struct {
738 // FieldByName returns the struct field with the given name.
739 // It returns the zero Value if no field was found.
740 // It panics if v's Kind is not struct.
741 func (v Value) FieldByName(name string) Value {
744 if f, ok := iv.typ.FieldByName(name); ok {
745 return v.FieldByIndex(f.Index)
750 // FieldByNameFunc returns the struct field with a name
751 // that satisfies the match function.
752 // It panics if v's Kind is not struct.
753 // It returns the zero Value if no field was found.
754 func (v Value) FieldByNameFunc(match func(string) bool) Value {
755 v.internal().mustBe(Struct)
756 if f, ok := v.Type().FieldByNameFunc(match); ok {
757 return v.FieldByIndex(f.Index)
762 // Float returns v's underlying value, as an float64.
763 // It panics if v's Kind is not Float32 or Float64
764 func (v Value) Float() float64 {
768 return float64(*(*float32)(iv.addr))
770 return *(*float64)(iv.addr)
772 panic(&ValueError{"reflect.Value.Float", iv.kind})
775 // Index returns v's i'th element.
776 // It panics if v's Kind is not Array or Slice or i is out of range.
777 func (v Value) Index(i int) Value {
781 panic(&ValueError{"reflect.Value.Index", iv.kind})
783 flag := iv.flag // element flag same as overall array
785 if i < 0 || i > t.Len() {
786 panic("reflect: array index out of range")
789 return valueFromValueOffset(flag, typ, iv, uintptr(i)*typ.Size())
792 // Element flag same as Elem of Ptr.
793 // Addressable, possibly read-only.
794 flag := iv.flag&flagRO | flagAddr
795 s := (*SliceHeader)(iv.addr)
796 if i < 0 || i >= s.Len {
797 panic("reflect: slice index out of range")
800 addr := unsafe.Pointer(s.Data + uintptr(i)*typ.Size())
801 return valueFromAddr(flag, typ, addr)
807 // Int returns v's underlying value, as an int64.
808 // It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64.
809 func (v Value) Int() int64 {
813 return int64(*(*int)(iv.addr))
815 return int64(*(*int8)(iv.addr))
817 return int64(*(*int16)(iv.addr))
819 return int64(*(*int32)(iv.addr))
821 return *(*int64)(iv.addr)
823 panic(&ValueError{"reflect.Value.Int", iv.kind})
826 // CanInterface returns true if Interface can be used without panicking.
827 func (v Value) CanInterface() bool {
829 if iv.kind == Invalid {
830 panic(&ValueError{"reflect.Value.CanInterface", iv.kind})
832 return v.InternalMethod == 0 && iv.flag&flagRO == 0
835 // Interface returns v's value as an interface{}.
836 // If v is a method obtained by invoking Value.Method
837 // (as opposed to Type.Method), Interface cannot return an
838 // interface value, so it panics.
839 func (v Value) Interface() interface{} {
840 return valueInterface(v, true)
843 func valueInterface(v Value, safe bool) interface{} {
845 return iv.valueInterface(safe)
848 func (iv internalValue) valueInterface(safe bool) interface{} {
850 panic(&ValueError{"reflect.Value.Interface", iv.kind})
853 panic("reflect.Value.Interface: cannot create interface value for method with bound receiver")
856 if safe && iv.flag&flagRO != 0 {
857 // Do not allow access to unexported values via Interface,
858 // because they might be pointers that should not be
859 // writable or methods or function that should not be callable.
860 panic("reflect.Value.Interface: cannot return value obtained from unexported field or method")
862 if iv.kind == Interface {
863 // Special case: return the element inside the interface.
864 // Won't recurse further because an interface cannot contain an interface.
868 return iv.Elem().Interface()
871 // Non-interface value.
872 var eface emptyInterface
873 eface.typ = iv.typ.runtimeType()
875 return *(*interface{})(unsafe.Pointer(&eface))
878 // InterfaceData returns the interface v's value as a uintptr pair.
879 // It panics if v's Kind is not Interface.
880 func (v Value) InterfaceData() [2]uintptr {
883 // We treat this as a read operation, so we allow
884 // it even for unexported data, because the caller
885 // has to import "unsafe" to turn it into something
886 // that can be abused.
887 return *(*[2]uintptr)(iv.addr)
890 // IsNil returns true if v is a nil value.
891 // It panics if v's Kind is not Chan, Func, Interface, Map, Ptr, or Slice.
892 func (v Value) IsNil() bool {
893 return v.internal().IsNil()
896 func (iv internalValue) IsNil() bool {
900 panic("reflect: IsNil of method Value")
903 case Chan, Func, Map:
905 panic("reflect: IsNil of method Value")
907 return *(*uintptr)(iv.addr) == 0
908 case Interface, Slice:
909 // Both interface and slice are nil if first word is 0.
910 return *(*uintptr)(iv.addr) == 0
912 panic(&ValueError{"reflect.Value.IsNil", iv.kind})
915 // IsValid returns true if v represents a value.
916 // It returns false if v is the zero Value.
917 // If IsValid returns false, all other methods except String panic.
918 // Most functions and methods never return an invalid value.
919 // If one does, its documentation states the conditions explicitly.
920 func (v Value) IsValid() bool {
921 return v.Internal != nil
924 // Kind returns v's Kind.
925 // If v is the zero Value (IsValid returns false), Kind returns Invalid.
926 func (v Value) Kind() Kind {
927 return v.internal().kind
930 // Len returns v's length.
931 // It panics if v's Kind is not Array, Chan, Map, Slice, or String.
932 func (v Value) Len() int {
938 return int(chanlen(*(*iword)(iv.addr)))
940 return int(maplen(*(*iword)(iv.addr)))
942 return (*SliceHeader)(iv.addr).Len
944 return (*StringHeader)(iv.addr).Len
946 panic(&ValueError{"reflect.Value.Len", iv.kind})
949 // MapIndex returns the value associated with key in the map v.
950 // It panics if v's Kind is not Map.
951 // It returns the zero Value if key is not found in the map or if v represents a nil map.
952 // As in Go, the key's value must be assignable to the map's key type.
953 func (v Value) MapIndex(key Value) Value {
956 typ := iv.typ.toType()
958 // Do not require ikey to be exported, so that DeepEqual
959 // and other programs can use all the keys returned by
960 // MapKeys as arguments to MapIndex. If either the map
961 // or the key is unexported, though, the result will be
962 // considered unexported.
964 ikey := key.internal()
965 ikey = convertForAssignment("reflect.Value.MapIndex", nil, typ.Key(), ikey)
970 flag := (iv.flag | ikey.flag) & flagRO
971 elemType := typ.Elem()
972 elemWord, ok := mapaccess(typ.runtimeType(), *(*iword)(iv.addr), ikey.word)
976 return valueFromIword(flag, elemType, elemWord)
979 // MapKeys returns a slice containing all the keys present in the map,
980 // in unspecified order.
981 // It panics if v's Kind is not Map.
982 // It returns an empty slice if v represents a nil map.
983 func (v Value) MapKeys() []Value {
986 keyType := iv.typ.Key()
988 flag := iv.flag & flagRO
989 m := *(*iword)(iv.addr)
994 it := mapiterinit(iv.typ.runtimeType(), m)
995 a := make([]Value, mlen)
997 for i = 0; i < len(a); i++ {
998 keyWord, ok := mapiterkey(it)
1002 a[i] = valueFromIword(flag, keyType, keyWord)
1008 // Method returns a function value corresponding to v's i'th method.
1009 // The arguments to a Call on the returned function should not include
1010 // a receiver; the returned function will always use v as the receiver.
1011 // Method panics if i is out of range.
1012 func (v Value) Method(i int) Value {
1014 if iv.kind == Invalid {
1015 panic(&ValueError{"reflect.Value.Method", Invalid})
1017 if i < 0 || i >= iv.typ.NumMethod() {
1018 panic("reflect: Method index out of range")
1020 return Value{v.Internal, i + 1}
1023 // NumMethod returns the number of methods in the value's method set.
1024 func (v Value) NumMethod() int {
1026 if iv.kind == Invalid {
1027 panic(&ValueError{"reflect.Value.NumMethod", Invalid})
1029 return iv.typ.NumMethod()
1032 // MethodByName returns a function value corresponding to the method
1033 // of v with the given name.
1034 // The arguments to a Call on the returned function should not include
1035 // a receiver; the returned function will always use v as the receiver.
1036 // It returns the zero Value if no method was found.
1037 func (v Value) MethodByName(name string) Value {
1039 if iv.kind == Invalid {
1040 panic(&ValueError{"reflect.Value.MethodByName", Invalid})
1042 m, ok := iv.typ.MethodByName(name)
1044 return Value{v.Internal, m.Index + 1}
1049 // NumField returns the number of fields in the struct v.
1050 // It panics if v's Kind is not Struct.
1051 func (v Value) NumField() int {
1054 return iv.typ.NumField()
1057 // OverflowComplex returns true if the complex128 x cannot be represented by v's type.
1058 // It panics if v's Kind is not Complex64 or Complex128.
1059 func (v Value) OverflowComplex(x complex128) bool {
1063 return overflowFloat32(real(x)) || overflowFloat32(imag(x))
1067 panic(&ValueError{"reflect.Value.OverflowComplex", iv.kind})
1070 // OverflowFloat returns true if the float64 x cannot be represented by v's type.
1071 // It panics if v's Kind is not Float32 or Float64.
1072 func (v Value) OverflowFloat(x float64) bool {
1076 return overflowFloat32(x)
1080 panic(&ValueError{"reflect.Value.OverflowFloat", iv.kind})
1083 func overflowFloat32(x float64) bool {
1087 return math.MaxFloat32 <= x && x <= math.MaxFloat64
1090 // OverflowInt returns true if the int64 x cannot be represented by v's type.
1091 // It panics if v's Kind is not Int, Int8, int16, Int32, or Int64.
1092 func (v Value) OverflowInt(x int64) bool {
1095 case Int, Int8, Int16, Int32, Int64:
1096 bitSize := iv.typ.size * 8
1097 trunc := (x << (64 - bitSize)) >> (64 - bitSize)
1100 panic(&ValueError{"reflect.Value.OverflowInt", iv.kind})
1103 // OverflowUint returns true if the uint64 x cannot be represented by v's type.
1104 // It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.
1105 func (v Value) OverflowUint(x uint64) bool {
1108 case Uint, Uintptr, Uint8, Uint16, Uint32, Uint64:
1109 bitSize := iv.typ.size * 8
1110 trunc := (x << (64 - bitSize)) >> (64 - bitSize)
1113 panic(&ValueError{"reflect.Value.OverflowUint", iv.kind})
1116 // Pointer returns v's value as a uintptr.
1117 // It returns uintptr instead of unsafe.Pointer so that
1118 // code using reflect cannot obtain unsafe.Pointers
1119 // without importing the unsafe package explicitly.
1120 // It panics if v's Kind is not Chan, Func, Map, Ptr, Slice, or UnsafePointer.
1121 func (v Value) Pointer() uintptr {
1124 case Ptr, UnsafePointer:
1125 if iv.kind == Func && v.InternalMethod != 0 {
1126 panic("reflect.Value.Pointer of method Value")
1128 return uintptr(iv.word)
1129 case Chan, Func, Map:
1130 if iv.kind == Func && v.InternalMethod != 0 {
1131 panic("reflect.Value.Pointer of method Value")
1133 return *(*uintptr)(iv.addr)
1135 return (*SliceHeader)(iv.addr).Data
1137 panic(&ValueError{"reflect.Value.Pointer", iv.kind})
1140 // Recv receives and returns a value from the channel v.
1141 // It panics if v's Kind is not Chan.
1142 // The receive blocks until a value is ready.
1143 // The boolean value ok is true if the value x corresponds to a send
1144 // on the channel, false if it is a zero value received because the channel is closed.
1145 func (v Value) Recv() (x Value, ok bool) {
1149 return iv.recv(false)
1152 // internal recv, possibly non-blocking (nb)
1153 func (iv internalValue) recv(nb bool) (val Value, ok bool) {
1154 t := iv.typ.toType()
1155 if t.ChanDir()&RecvDir == 0 {
1156 panic("recv on send-only channel")
1158 ch := *(*iword)(iv.addr)
1160 panic("recv on nil channel")
1162 valWord, selected, ok := chanrecv(iv.typ.runtimeType(), ch, nb)
1164 val = valueFromIword(0, t.Elem(), valWord)
1169 // Send sends x on the channel v.
1170 // It panics if v's kind is not Chan or if x's type is not the same type as v's element type.
1171 // As in Go, x's value must be assignable to the channel's element type.
1172 func (v Value) Send(x Value) {
1179 // internal send, possibly non-blocking
1180 func (iv internalValue) send(x Value, nb bool) (selected bool) {
1181 t := iv.typ.toType()
1182 if t.ChanDir()&SendDir == 0 {
1183 panic("send on recv-only channel")
1186 ix.mustBeExported() // do not let unexported x leak
1187 ix = convertForAssignment("reflect.Value.Send", nil, t.Elem(), ix)
1188 ch := *(*iword)(iv.addr)
1190 panic("send on nil channel")
1192 return chansend(iv.typ.runtimeType(), ch, ix.word, nb)
1195 // Set assigns x to the value v.
1196 // It panics if CanSet returns false.
1197 // As in Go, x's value must be assignable to v's type.
1198 func (v Value) Set(x Value) {
1202 iv.mustBeAssignable()
1203 ix.mustBeExported() // do not let unexported x leak
1205 ix = convertForAssignment("reflect.Set", iv.addr, iv.typ, ix)
1208 if Kind(ix.typ.kind) == Ptr || Kind(ix.typ.kind) == UnsafePointer {
1209 storeIword(iv.addr, ix.word, n)
1211 memmove(iv.addr, ix.addr, n)
1215 // SetBool sets v's underlying value.
1216 // It panics if v's Kind is not Bool or if CanSet() is false.
1217 func (v Value) SetBool(x bool) {
1219 iv.mustBeAssignable()
1221 *(*bool)(iv.addr) = x
1224 // SetComplex sets v's underlying value to x.
1225 // It panics if v's Kind is not Complex64 or Complex128, or if CanSet() is false.
1226 func (v Value) SetComplex(x complex128) {
1228 iv.mustBeAssignable()
1231 panic(&ValueError{"reflect.Value.SetComplex", iv.kind})
1233 *(*complex64)(iv.addr) = complex64(x)
1235 *(*complex128)(iv.addr) = x
1239 // SetFloat sets v's underlying value to x.
1240 // It panics if v's Kind is not Float32 or Float64, or if CanSet() is false.
1241 func (v Value) SetFloat(x float64) {
1243 iv.mustBeAssignable()
1246 panic(&ValueError{"reflect.Value.SetFloat", iv.kind})
1248 *(*float32)(iv.addr) = float32(x)
1250 *(*float64)(iv.addr) = x
1254 // SetInt sets v's underlying value to x.
1255 // It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64, or if CanSet() is false.
1256 func (v Value) SetInt(x int64) {
1258 iv.mustBeAssignable()
1261 panic(&ValueError{"reflect.Value.SetInt", iv.kind})
1263 *(*int)(iv.addr) = int(x)
1265 *(*int8)(iv.addr) = int8(x)
1267 *(*int16)(iv.addr) = int16(x)
1269 *(*int32)(iv.addr) = int32(x)
1271 *(*int64)(iv.addr) = x
1275 // SetLen sets v's length to n.
1276 // It panics if v's Kind is not Slice.
1277 func (v Value) SetLen(n int) {
1279 iv.mustBeAssignable()
1281 s := (*SliceHeader)(iv.addr)
1282 if n < 0 || n > int(s.Cap) {
1283 panic("reflect: slice length out of range in SetLen")
1288 // SetMapIndex sets the value associated with key in the map v to val.
1289 // It panics if v's Kind is not Map.
1290 // If val is the zero Value, SetMapIndex deletes the key from the map.
1291 // As in Go, key's value must be assignable to the map's key type,
1292 // and val's value must be assignable to the map's value type.
1293 func (v Value) SetMapIndex(key, val Value) {
1295 ikey := key.internal()
1296 ival := val.internal()
1301 ikey.mustBeExported()
1302 ikey = convertForAssignment("reflect.Value.SetMapIndex", nil, iv.typ.Key(), ikey)
1304 if ival.kind != Invalid {
1305 ival.mustBeExported()
1306 ival = convertForAssignment("reflect.Value.SetMapIndex", nil, iv.typ.Elem(), ival)
1309 mapassign(iv.typ.runtimeType(), *(*iword)(iv.addr), ikey.word, ival.word, ival.kind != Invalid)
1312 // SetUint sets v's underlying value to x.
1313 // It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64, or if CanSet() is false.
1314 func (v Value) SetUint(x uint64) {
1316 iv.mustBeAssignable()
1319 panic(&ValueError{"reflect.Value.SetUint", iv.kind})
1321 *(*uint)(iv.addr) = uint(x)
1323 *(*uint8)(iv.addr) = uint8(x)
1325 *(*uint16)(iv.addr) = uint16(x)
1327 *(*uint32)(iv.addr) = uint32(x)
1329 *(*uint64)(iv.addr) = x
1331 *(*uintptr)(iv.addr) = uintptr(x)
1335 // SetPointer sets the unsafe.Pointer value v to x.
1336 // It panics if v's Kind is not UnsafePointer.
1337 func (v Value) SetPointer(x unsafe.Pointer) {
1339 iv.mustBeAssignable()
1340 iv.mustBe(UnsafePointer)
1341 *(*unsafe.Pointer)(iv.addr) = x
1344 // SetString sets v's underlying value to x.
1345 // It panics if v's Kind is not String or if CanSet() is false.
1346 func (v Value) SetString(x string) {
1348 iv.mustBeAssignable()
1350 *(*string)(iv.addr) = x
1353 // Slice returns a slice of v.
1354 // It panics if v's Kind is not Array or Slice.
1355 func (v Value) Slice(beg, end int) Value {
1357 if iv.kind != Array && iv.kind != Slice {
1358 panic(&ValueError{"reflect.Value.Slice", iv.kind})
1361 if beg < 0 || end < beg || end > cap {
1362 panic("reflect.Value.Slice: slice index out of bounds")
1368 if iv.flag&flagAddr == 0 {
1369 panic("reflect.Value.Slice: slice of unaddressable array")
1371 typ = toType((*arrayType)(unsafe.Pointer(iv.typ)).slice)
1372 base = uintptr(iv.addr)
1374 typ = iv.typ.toType()
1375 base = (*SliceHeader)(iv.addr).Data
1377 s := new(SliceHeader)
1378 s.Data = base + uintptr(beg)*typ.Elem().Size()
1381 return valueFromAddr(iv.flag&flagRO, typ, unsafe.Pointer(s))
1384 // String returns the string v's underlying value, as a string.
1385 // String is a special case because of Go's String method convention.
1386 // Unlike the other getters, it does not panic if v's Kind is not String.
1387 // Instead, it returns a string of the form "<T value>" where T is v's type.
1388 func (v Value) String() string {
1392 return "<invalid Value>"
1394 return *(*string)(iv.addr)
1396 return "<" + iv.typ.String() + " Value>"
1399 // TryRecv attempts to receive a value from the channel v but will not block.
1400 // It panics if v's Kind is not Chan.
1401 // If the receive cannot finish without blocking, x is the zero Value.
1402 // The boolean ok is true if the value x corresponds to a send
1403 // on the channel, false if it is a zero value received because the channel is closed.
1404 func (v Value) TryRecv() (x Value, ok bool) {
1408 return iv.recv(true)
1411 // TrySend attempts to send x on the channel v but will not block.
1412 // It panics if v's Kind is not Chan.
1413 // It returns true if the value was sent, false otherwise.
1414 // As in Go, x's value must be assignable to the channel's element type.
1415 func (v Value) TrySend(x Value) bool {
1419 return iv.send(x, true)
1422 // Type returns v's type.
1423 func (v Value) Type() Type {
1424 t := v.internal().typ
1426 panic(&ValueError{"reflect.Value.Type", Invalid})
1431 // Uint returns v's underlying value, as a uint64.
1432 // It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64.
1433 func (v Value) Uint() uint64 {
1437 return uint64(*(*uint)(iv.addr))
1439 return uint64(*(*uint8)(iv.addr))
1441 return uint64(*(*uint16)(iv.addr))
1443 return uint64(*(*uint32)(iv.addr))
1445 return uint64(*(*uintptr)(iv.addr))
1447 return *(*uint64)(iv.addr)
1449 panic(&ValueError{"reflect.Value.Uint", iv.kind})
1452 // UnsafeAddr returns a pointer to v's data.
1453 // It is for advanced clients that also import the "unsafe" package.
1454 // It panics if v is not addressable.
1455 func (v Value) UnsafeAddr() uintptr {
1457 if iv.kind == Invalid {
1458 panic(&ValueError{"reflect.Value.UnsafeAddr", iv.kind})
1460 if iv.flag&flagAddr == 0 {
1461 panic("reflect.Value.UnsafeAddr of unaddressable value")
1463 return uintptr(iv.addr)
1466 // StringHeader is the runtime representation of a string.
1467 // It cannot be used safely or portably.
1468 type StringHeader struct {
1473 // SliceHeader is the runtime representation of a slice.
1474 // It cannot be used safely or portably.
1475 type SliceHeader struct {
1481 func typesMustMatch(what string, t1, t2 Type) {
1483 panic("reflect: " + what + ": " + t1.String() + " != " + t2.String())
1487 // grow grows the slice s so that it can hold extra more values, allocating
1488 // more capacity if needed. It also returns the old and new slice lengths.
1489 func grow(s Value, extra int) (Value, int, int) {
1493 panic("reflect.Append: slice overflow")
1497 return s.Slice(0, i1), i0, i1
1510 t := MakeSlice(s.Type(), i1, m)
1515 // Append appends the values x to a slice s and returns the resulting slice.
1516 // As in Go, each x's value must be assignable to the slice's element type.
1517 func Append(s Value, x ...Value) Value {
1518 s.internal().mustBe(Slice)
1519 s, i0, i1 := grow(s, len(x))
1520 for i, j := i0, 0; i < i1; i, j = i+1, j+1 {
1521 s.Index(i).Set(x[j])
1526 // AppendSlice appends a slice t to a slice s and returns the resulting slice.
1527 // The slices s and t must have the same element type.
1528 func AppendSlice(s, t Value) Value {
1529 s.internal().mustBe(Slice)
1530 t.internal().mustBe(Slice)
1531 typesMustMatch("reflect.AppendSlice", s.Type().Elem(), t.Type().Elem())
1532 s, i0, i1 := grow(s, t.Len())
1533 Copy(s.Slice(i0, i1), t)
1537 // Copy copies the contents of src into dst until either
1538 // dst has been filled or src has been exhausted.
1539 // It returns the number of elements copied.
1540 // Dst and src each must have kind Slice or Array, and
1541 // dst and src must have the same element type.
1542 func Copy(dst, src Value) int {
1543 idst := dst.internal()
1544 isrc := src.internal()
1546 if idst.kind != Array && idst.kind != Slice {
1547 panic(&ValueError{"reflect.Copy", idst.kind})
1549 if idst.kind == Array {
1550 idst.mustBeAssignable()
1552 idst.mustBeExported()
1553 if isrc.kind != Array && isrc.kind != Slice {
1554 panic(&ValueError{"reflect.Copy", isrc.kind})
1556 isrc.mustBeExported()
1558 de := idst.typ.Elem()
1559 se := isrc.typ.Elem()
1560 typesMustMatch("reflect.Copy", de, se)
1563 if sn := src.Len(); n > sn {
1567 // If sk is an in-line array, cannot take its address.
1568 // Instead, copy element by element.
1569 if isrc.addr == nil {
1570 for i := 0; i < n; i++ {
1571 dst.Index(i).Set(src.Index(i))
1576 // Copy via memmove.
1577 var da, sa unsafe.Pointer
1578 if idst.kind == Array {
1581 da = unsafe.Pointer((*SliceHeader)(idst.addr).Data)
1583 if isrc.kind == Array {
1586 sa = unsafe.Pointer((*SliceHeader)(isrc.addr).Data)
1588 memmove(da, sa, uintptr(n)*de.Size())
1596 // MakeSlice creates a new zero-initialized slice value
1597 // for the specified slice type, length, and capacity.
1598 func MakeSlice(typ Type, len, cap int) Value {
1599 if typ.Kind() != Slice {
1600 panic("reflect: MakeSlice of non-slice type")
1603 Data: uintptr(unsafe.NewArray(typ.Elem(), cap)),
1607 return valueFromAddr(0, typ, unsafe.Pointer(s))
1610 // MakeChan creates a new channel with the specified type and buffer size.
1611 func MakeChan(typ Type, buffer int) Value {
1612 if typ.Kind() != Chan {
1613 panic("reflect: MakeChan of non-chan type")
1616 panic("MakeChan: negative buffer size")
1618 if typ.ChanDir() != BothDir {
1619 panic("MakeChan: unidirectional channel type")
1621 ch := makechan(typ.runtimeType(), uint32(buffer))
1622 return valueFromIword(0, typ, ch)
1625 // MakeMap creates a new map of the specified type.
1626 func MakeMap(typ Type) Value {
1627 if typ.Kind() != Map {
1628 panic("reflect: MakeMap of non-map type")
1630 m := makemap(typ.runtimeType())
1631 return valueFromIword(0, typ, m)
1634 // Indirect returns the value that v points to.
1635 // If v is a nil pointer, Indirect returns a nil Value.
1636 // If v is not a pointer, Indirect returns v.
1637 func Indirect(v Value) Value {
1638 if v.Kind() != Ptr {
1644 // ValueOf returns a new Value initialized to the concrete value
1645 // stored in the interface i. ValueOf(nil) returns the zero Value.
1646 func ValueOf(i interface{}) Value {
1650 // For an interface value with the noAddr bit set,
1651 // the representation is identical to an empty interface.
1652 eface := *(*emptyInterface)(unsafe.Pointer(&i))
1653 return packValue(0, eface.typ, eface.word)
1656 // Zero returns a Value representing a zero value for the specified type.
1657 // The result is different from the zero value of the Value struct,
1658 // which represents no value at all.
1659 // For example, Zero(TypeOf(42)) returns a Value with Kind Int and value 0.
1660 func Zero(typ Type) Value {
1662 panic("reflect: Zero(nil)")
1664 if typ.Kind() == Ptr || typ.Kind() == UnsafePointer {
1665 return valueFromIword(0, typ, 0)
1667 return valueFromAddr(0, typ, unsafe.New(typ))
1670 // New returns a Value representing a pointer to a new zero value
1671 // for the specified type. That is, the returned Value's Type is PtrTo(t).
1672 func New(typ Type) Value {
1674 panic("reflect: New(nil)")
1676 ptr := unsafe.New(typ)
1677 return valueFromIword(0, PtrTo(typ), iword(uintptr(ptr)))
1680 // convertForAssignment
1681 func convertForAssignment(what string, addr unsafe.Pointer, dst Type, iv internalValue) internalValue {
1683 panic(what + ": cannot assign method value to type " + dst.String())
1686 dst1 := dst.(*commonType)
1687 if directlyAssignable(dst1, iv.typ) {
1688 // Overwrite type so that they match.
1689 // Same memory layout, so no harm done.
1693 if implements(dst1, iv.typ) {
1695 addr = unsafe.Pointer(new(interface{}))
1697 x := iv.valueInterface(false)
1698 if dst.NumMethod() == 0 {
1699 *(*interface{})(addr) = x
1701 ifaceE2I(dst1.runtimeType(), x, addr)
1704 iv.word = iword(uintptr(addr))
1710 panic(what + ": value of type " + iv.typ.String() + " is not assignable to type " + dst.String())
1713 // implemented in ../pkg/runtime
1714 func chancap(ch iword) int32
1715 func chanclose(ch iword)
1716 func chanlen(ch iword) int32
1717 func chanrecv(t *runtime.Type, ch iword, nb bool) (val iword, selected, received bool)
1718 func chansend(t *runtime.Type, ch iword, val iword, nb bool) bool
1720 func makechan(typ *runtime.Type, size uint32) (ch iword)
1721 func makemap(t *runtime.Type) iword
1722 func mapaccess(t *runtime.Type, m iword, key iword) (val iword, ok bool)
1723 func mapassign(t *runtime.Type, m iword, key, val iword, ok bool)
1724 func mapiterinit(t *runtime.Type, m iword) *byte
1725 func mapiterkey(it *byte) (key iword, ok bool)
1726 func mapiternext(it *byte)
1727 func maplen(m iword) int32
1729 func call(typ *commonType, fnaddr unsafe.Pointer, isInterface bool, isMethod bool, params *unsafe.Pointer, results *unsafe.Pointer)
1730 func ifaceE2I(t *runtime.Type, src interface{}, dst unsafe.Pointer)