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. 4 5package reflect 6 7import ( 8 "math" 9 "runtime" 10 "unsafe" 11) 12 13const ptrSize = 4 << (^uintptr(0) >> 63) // unsafe.Sizeof(uintptr(0)) but an ideal const 14 15// Value is the reflection interface to a Go value. 16// 17// Not all methods apply to all kinds of values. Restrictions, 18// if any, are noted in the documentation for each method. 19// Use the Kind method to find out the kind of value before 20// calling kind-specific methods. Calling a method 21// inappropriate to the kind of type causes a run time panic. 22// 23// The zero Value represents no value. 24// Its IsValid method returns false, its Kind method returns Invalid, 25// its String method returns "<invalid Value>", and all other methods panic. 26// Most functions and methods never return an invalid value. 27// If one does, its documentation states the conditions explicitly. 28// 29// A Value can be used concurrently by multiple goroutines provided that 30// the underlying Go value can be used concurrently for the equivalent 31// direct operations. 32// 33// To compare two Values, compare the results of the Interface method. 34// Using == on two Values does not compare the underlying values 35// they represent. 36type Value struct { 37 // typ holds the type of the value represented by a Value. 38 typ *rtype 39 40 // Pointer-valued data or, if flagIndir is set, pointer to data. 41 // Valid when either flagIndir is set or typ.pointers() is true. 42 ptr unsafe.Pointer 43 44 // flag holds metadata about the value. 45 // The lowest bits are flag bits: 46 // - flagStickyRO: obtained via unexported not embedded field, so read-only 47 // - flagEmbedRO: obtained via unexported embedded field, so read-only 48 // - flagIndir: val holds a pointer to the data 49 // - flagAddr: v.CanAddr is true (implies flagIndir) 50 // - flagMethod: v is a method value. 51 // The next five bits give the Kind of the value. 52 // This repeats typ.Kind() except for method values. 53 // The remaining 23+ bits give a method number for method values. 54 // If flag.kind() != Func, code can assume that flagMethod is unset. 55 // If ifaceIndir(typ), code can assume that flagIndir is set. 56 flag 57 58 // A method value represents a curried method invocation 59 // like r.Read for some receiver r. The typ+val+flag bits describe 60 // the receiver r, but the flag's Kind bits say Func (methods are 61 // functions), and the top bits of the flag give the method number 62 // in r's type's method table. 63} 64 65type flag uintptr 66 67const ( 68 flagKindWidth = 5 // there are 27 kinds 69 flagKindMask flag = 1<<flagKindWidth - 1 70 flagStickyRO flag = 1 << 5 71 flagEmbedRO flag = 1 << 6 72 flagIndir flag = 1 << 7 73 flagAddr flag = 1 << 8 74 flagMethod flag = 1 << 9 75 flagMethodFn flag = 1 << 10 // gccgo: first fn parameter is always pointer 76 flagMethodShift = 11 77 flagRO flag = flagStickyRO | flagEmbedRO 78) 79 80func (f flag) kind() Kind { 81 return Kind(f & flagKindMask) 82} 83 84func (f flag) ro() flag { 85 if f&flagRO != 0 { 86 return flagStickyRO 87 } 88 return 0 89} 90 91// pointer returns the underlying pointer represented by v. 92// v.Kind() must be Ptr, Map, Chan, Func, or UnsafePointer 93func (v Value) pointer() unsafe.Pointer { 94 if v.typ.size != ptrSize || !v.typ.pointers() { 95 panic("can't call pointer on a non-pointer Value") 96 } 97 if v.flag&flagIndir != 0 { 98 return *(*unsafe.Pointer)(v.ptr) 99 } 100 return v.ptr 101} 102 103// packEface converts v to the empty interface. 104func packEface(v Value) interface{} { 105 t := v.typ 106 var i interface{} 107 e := (*emptyInterface)(unsafe.Pointer(&i)) 108 // First, fill in the data portion of the interface. 109 switch { 110 case ifaceIndir(t): 111 if v.flag&flagIndir == 0 { 112 panic("bad indir") 113 } 114 // Value is indirect, and so is the interface we're making. 115 ptr := v.ptr 116 if v.flag&flagAddr != 0 { 117 // TODO: pass safe boolean from valueInterface so 118 // we don't need to copy if safe==true? 119 c := unsafe_New(t) 120 typedmemmove(t, c, ptr) 121 ptr = c 122 } 123 e.word = ptr 124 case v.flag&flagIndir != 0: 125 // Value is indirect, but interface is direct. We need 126 // to load the data at v.ptr into the interface data word. 127 e.word = *(*unsafe.Pointer)(v.ptr) 128 default: 129 // Value is direct, and so is the interface. 130 e.word = v.ptr 131 } 132 // Now, fill in the type portion. We're very careful here not 133 // to have any operation between the e.word and e.typ assignments 134 // that would let the garbage collector observe the partially-built 135 // interface value. 136 e.typ = t 137 return i 138} 139 140// unpackEface converts the empty interface i to a Value. 141func unpackEface(i interface{}) Value { 142 e := (*emptyInterface)(unsafe.Pointer(&i)) 143 // NOTE: don't read e.word until we know whether it is really a pointer or not. 144 t := e.typ 145 if t == nil { 146 return Value{} 147 } 148 f := flag(t.Kind()) 149 if ifaceIndir(t) { 150 f |= flagIndir 151 } 152 return Value{t, e.word, f} 153} 154 155// A ValueError occurs when a Value method is invoked on 156// a Value that does not support it. Such cases are documented 157// in the description of each method. 158type ValueError struct { 159 Method string 160 Kind Kind 161} 162 163func (e *ValueError) Error() string { 164 if e.Kind == 0 { 165 return "reflect: call of " + e.Method + " on zero Value" 166 } 167 return "reflect: call of " + e.Method + " on " + e.Kind.String() + " Value" 168} 169 170// methodName returns the name of the calling method, 171// assumed to be two stack frames above. 172func methodName() string { 173 pc, _, _, _ := runtime.Caller(2) 174 f := runtime.FuncForPC(pc) 175 if f == nil { 176 return "unknown method" 177 } 178 return f.Name() 179} 180 181// emptyInterface is the header for an interface{} value. 182type emptyInterface struct { 183 typ *rtype 184 word unsafe.Pointer 185} 186 187// nonEmptyInterface is the header for an interface value with methods. 188type nonEmptyInterface struct { 189 // see ../runtime/iface.go:/Itab 190 itab *struct { 191 typ *rtype // dynamic concrete type 192 fun [100000]unsafe.Pointer // method table 193 } 194 word unsafe.Pointer 195} 196 197// mustBe panics if f's kind is not expected. 198// Making this a method on flag instead of on Value 199// (and embedding flag in Value) means that we can write 200// the very clear v.mustBe(Bool) and have it compile into 201// v.flag.mustBe(Bool), which will only bother to copy the 202// single important word for the receiver. 203func (f flag) mustBe(expected Kind) { 204 if f.kind() != expected { 205 panic(&ValueError{methodName(), f.kind()}) 206 } 207} 208 209// mustBeExported panics if f records that the value was obtained using 210// an unexported field. 211func (f flag) mustBeExported() { 212 if f == 0 { 213 panic(&ValueError{methodName(), 0}) 214 } 215 if f&flagRO != 0 { 216 panic("reflect: " + methodName() + " using value obtained using unexported field") 217 } 218} 219 220// mustBeAssignable panics if f records that the value is not assignable, 221// which is to say that either it was obtained using an unexported field 222// or it is not addressable. 223func (f flag) mustBeAssignable() { 224 if f == 0 { 225 panic(&ValueError{methodName(), Invalid}) 226 } 227 // Assignable if addressable and not read-only. 228 if f&flagRO != 0 { 229 panic("reflect: " + methodName() + " using value obtained using unexported field") 230 } 231 if f&flagAddr == 0 { 232 panic("reflect: " + methodName() + " using unaddressable value") 233 } 234} 235 236// Addr returns a pointer value representing the address of v. 237// It panics if CanAddr() returns false. 238// Addr is typically used to obtain a pointer to a struct field 239// or slice element in order to call a method that requires a 240// pointer receiver. 241func (v Value) Addr() Value { 242 if v.flag&flagAddr == 0 { 243 panic("reflect.Value.Addr of unaddressable value") 244 } 245 return Value{v.typ.ptrTo(), v.ptr, v.flag.ro() | flag(Ptr)} 246} 247 248// Bool returns v's underlying value. 249// It panics if v's kind is not Bool. 250func (v Value) Bool() bool { 251 v.mustBe(Bool) 252 return *(*bool)(v.ptr) 253} 254 255// Bytes returns v's underlying value. 256// It panics if v's underlying value is not a slice of bytes. 257func (v Value) Bytes() []byte { 258 v.mustBe(Slice) 259 if v.typ.Elem().Kind() != Uint8 { 260 panic("reflect.Value.Bytes of non-byte slice") 261 } 262 // Slice is always bigger than a word; assume flagIndir. 263 return *(*[]byte)(v.ptr) 264} 265 266// runes returns v's underlying value. 267// It panics if v's underlying value is not a slice of runes (int32s). 268func (v Value) runes() []rune { 269 v.mustBe(Slice) 270 if v.typ.Elem().Kind() != Int32 { 271 panic("reflect.Value.Bytes of non-rune slice") 272 } 273 // Slice is always bigger than a word; assume flagIndir. 274 return *(*[]rune)(v.ptr) 275} 276 277// CanAddr reports whether the value's address can be obtained with Addr. 278// Such values are called addressable. A value is addressable if it is 279// an element of a slice, an element of an addressable array, 280// a field of an addressable struct, or the result of dereferencing a pointer. 281// If CanAddr returns false, calling Addr will panic. 282func (v Value) CanAddr() bool { 283 return v.flag&flagAddr != 0 284} 285 286// CanSet reports whether the value of v can be changed. 287// A Value can be changed only if it is addressable and was not 288// obtained by the use of unexported struct fields. 289// If CanSet returns false, calling Set or any type-specific 290// setter (e.g., SetBool, SetInt) will panic. 291func (v Value) CanSet() bool { 292 return v.flag&(flagAddr|flagRO) == flagAddr 293} 294 295// Call calls the function v with the input arguments in. 296// For example, if len(in) == 3, v.Call(in) represents the Go call v(in[0], in[1], in[2]). 297// Call panics if v's Kind is not Func. 298// It returns the output results as Values. 299// As in Go, each input argument must be assignable to the 300// type of the function's corresponding input parameter. 301// If v is a variadic function, Call creates the variadic slice parameter 302// itself, copying in the corresponding values. 303func (v Value) Call(in []Value) []Value { 304 v.mustBe(Func) 305 v.mustBeExported() 306 return v.call("Call", in) 307} 308 309// CallSlice calls the variadic function v with the input arguments in, 310// assigning the slice in[len(in)-1] to v's final variadic argument. 311// For example, if len(in) == 3, v.CallSlice(in) represents the Go call v(in[0], in[1], in[2]...). 312// CallSlice panics if v's Kind is not Func or if v is not variadic. 313// It returns the output results as Values. 314// As in Go, each input argument must be assignable to the 315// type of the function's corresponding input parameter. 316func (v Value) CallSlice(in []Value) []Value { 317 v.mustBe(Func) 318 v.mustBeExported() 319 return v.call("CallSlice", in) 320} 321 322var callGC bool // for testing; see TestCallMethodJump 323 324func (v Value) call(op string, in []Value) []Value { 325 // Get function pointer, type. 326 t := v.typ 327 var ( 328 fn unsafe.Pointer 329 rcvr Value 330 ) 331 if v.flag&flagMethod != 0 { 332 rcvr = v 333 _, t, fn = methodReceiver(op, v, int(v.flag)>>flagMethodShift) 334 } else if v.flag&flagIndir != 0 { 335 fn = *(*unsafe.Pointer)(v.ptr) 336 } else { 337 fn = v.ptr 338 } 339 340 if fn == nil { 341 panic("reflect.Value.Call: call of nil function") 342 } 343 344 isSlice := op == "CallSlice" 345 n := t.NumIn() 346 if isSlice { 347 if !t.IsVariadic() { 348 panic("reflect: CallSlice of non-variadic function") 349 } 350 if len(in) < n { 351 panic("reflect: CallSlice with too few input arguments") 352 } 353 if len(in) > n { 354 panic("reflect: CallSlice with too many input arguments") 355 } 356 } else { 357 if t.IsVariadic() { 358 n-- 359 } 360 if len(in) < n { 361 panic("reflect: Call with too few input arguments") 362 } 363 if !t.IsVariadic() && len(in) > n { 364 panic("reflect: Call with too many input arguments") 365 } 366 } 367 for _, x := range in { 368 if x.Kind() == Invalid { 369 panic("reflect: " + op + " using zero Value argument") 370 } 371 } 372 for i := 0; i < n; i++ { 373 if xt, targ := in[i].Type(), t.In(i); !xt.AssignableTo(targ) { 374 panic("reflect: " + op + " using " + xt.String() + " as type " + targ.String()) 375 } 376 } 377 if !isSlice && t.IsVariadic() { 378 // prepare slice for remaining values 379 m := len(in) - n 380 slice := MakeSlice(t.In(n), m, m) 381 elem := t.In(n).Elem() 382 for i := 0; i < m; i++ { 383 x := in[n+i] 384 if xt := x.Type(); !xt.AssignableTo(elem) { 385 panic("reflect: cannot use " + xt.String() + " as type " + elem.String() + " in " + op) 386 } 387 slice.Index(i).Set(x) 388 } 389 origIn := in 390 in = make([]Value, n+1) 391 copy(in[:n], origIn) 392 in[n] = slice 393 } 394 395 nin := len(in) 396 if nin != t.NumIn() { 397 panic("reflect.Value.Call: wrong argument count") 398 } 399 nout := t.NumOut() 400 401 if v.flag&flagMethod != 0 { 402 nin++ 403 } 404 firstPointer := len(in) > 0 && t.In(0).Kind() != Ptr && v.flag&flagMethodFn != 0 405 params := make([]unsafe.Pointer, nin) 406 off := 0 407 if v.flag&flagMethod != 0 { 408 // Hard-wired first argument. 409 p := new(unsafe.Pointer) 410 if rcvr.typ.Kind() == Interface { 411 *p = unsafe.Pointer((*nonEmptyInterface)(v.ptr).word) 412 } else if rcvr.typ.Kind() == Ptr || rcvr.typ.Kind() == UnsafePointer { 413 *p = rcvr.pointer() 414 } else { 415 *p = rcvr.ptr 416 } 417 params[0] = unsafe.Pointer(p) 418 off = 1 419 } 420 for i, pv := range in { 421 pv.mustBeExported() 422 targ := t.In(i).(*rtype) 423 pv = pv.assignTo("reflect.Value.Call", targ, nil) 424 if pv.flag&flagIndir == 0 { 425 p := new(unsafe.Pointer) 426 *p = pv.ptr 427 params[off] = unsafe.Pointer(p) 428 } else { 429 params[off] = pv.ptr 430 } 431 if i == 0 && firstPointer { 432 p := new(unsafe.Pointer) 433 *p = params[off] 434 params[off] = unsafe.Pointer(p) 435 } 436 off++ 437 } 438 439 ret := make([]Value, nout) 440 results := make([]unsafe.Pointer, nout) 441 for i := 0; i < nout; i++ { 442 tv := t.Out(i) 443 v := New(tv) 444 results[i] = v.pointer() 445 fl := flagIndir | flag(tv.Kind()) 446 ret[i] = Value{tv.common(), v.pointer(), fl} 447 } 448 449 var pp *unsafe.Pointer 450 if len(params) > 0 { 451 pp = ¶ms[0] 452 } 453 var pr *unsafe.Pointer 454 if len(results) > 0 { 455 pr = &results[0] 456 } 457 458 call(t, fn, v.flag&flagMethod != 0, firstPointer, pp, pr) 459 460 // For testing; see TestCallMethodJump. 461 if callGC { 462 runtime.GC() 463 } 464 465 return ret 466} 467 468// methodReceiver returns information about the receiver 469// described by v. The Value v may or may not have the 470// flagMethod bit set, so the kind cached in v.flag should 471// not be used. 472// The return value rcvrtype gives the method's actual receiver type. 473// The return value t gives the method type signature (without the receiver). 474// The return value fn is a pointer to the method code. 475func methodReceiver(op string, v Value, methodIndex int) (rcvrtype, t *rtype, fn unsafe.Pointer) { 476 i := methodIndex 477 if v.typ.Kind() == Interface { 478 tt := (*interfaceType)(unsafe.Pointer(v.typ)) 479 if uint(i) >= uint(len(tt.methods)) { 480 panic("reflect: internal error: invalid method index") 481 } 482 m := &tt.methods[i] 483 if m.pkgPath != nil { 484 panic("reflect: " + op + " of unexported method") 485 } 486 iface := (*nonEmptyInterface)(v.ptr) 487 if iface.itab == nil { 488 panic("reflect: " + op + " of method on nil interface value") 489 } 490 rcvrtype = iface.itab.typ 491 fn = unsafe.Pointer(&iface.itab.fun[i]) 492 t = m.typ 493 } else { 494 rcvrtype = v.typ 495 ms := v.typ.exportedMethods() 496 if uint(i) >= uint(len(ms)) { 497 panic("reflect: internal error: invalid method index") 498 } 499 m := ms[i] 500 if m.pkgPath != nil { 501 panic("reflect: " + op + " of unexported method") 502 } 503 fn = unsafe.Pointer(&m.tfn) 504 t = m.mtyp 505 } 506 return 507} 508 509// v is a method receiver. Store at p the word which is used to 510// encode that receiver at the start of the argument list. 511// Reflect uses the "interface" calling convention for 512// methods, which always uses one word to record the receiver. 513func storeRcvr(v Value, p unsafe.Pointer) { 514 t := v.typ 515 if t.Kind() == Interface { 516 // the interface data word becomes the receiver word 517 iface := (*nonEmptyInterface)(v.ptr) 518 *(*unsafe.Pointer)(p) = iface.word 519 } else if v.flag&flagIndir != 0 && !ifaceIndir(t) { 520 *(*unsafe.Pointer)(p) = *(*unsafe.Pointer)(v.ptr) 521 } else { 522 *(*unsafe.Pointer)(p) = v.ptr 523 } 524} 525 526// align returns the result of rounding x up to a multiple of n. 527// n must be a power of two. 528func align(x, n uintptr) uintptr { 529 return (x + n - 1) &^ (n - 1) 530} 531 532// funcName returns the name of f, for use in error messages. 533func funcName(f func([]Value) []Value) string { 534 pc := *(*uintptr)(unsafe.Pointer(&f)) 535 rf := runtime.FuncForPC(pc) 536 if rf != nil { 537 return rf.Name() 538 } 539 return "closure" 540} 541 542// Cap returns v's capacity. 543// It panics if v's Kind is not Array, Chan, or Slice. 544func (v Value) Cap() int { 545 k := v.kind() 546 switch k { 547 case Array: 548 return v.typ.Len() 549 case Chan: 550 return chancap(v.pointer()) 551 case Slice: 552 // Slice is always bigger than a word; assume flagIndir. 553 return (*sliceHeader)(v.ptr).Cap 554 } 555 panic(&ValueError{"reflect.Value.Cap", v.kind()}) 556} 557 558// Close closes the channel v. 559// It panics if v's Kind is not Chan. 560func (v Value) Close() { 561 v.mustBe(Chan) 562 v.mustBeExported() 563 chanclose(v.pointer()) 564} 565 566// Complex returns v's underlying value, as a complex128. 567// It panics if v's Kind is not Complex64 or Complex128 568func (v Value) Complex() complex128 { 569 k := v.kind() 570 switch k { 571 case Complex64: 572 return complex128(*(*complex64)(v.ptr)) 573 case Complex128: 574 return *(*complex128)(v.ptr) 575 } 576 panic(&ValueError{"reflect.Value.Complex", v.kind()}) 577} 578 579// Elem returns the value that the interface v contains 580// or that the pointer v points to. 581// It panics if v's Kind is not Interface or Ptr. 582// It returns the zero Value if v is nil. 583func (v Value) Elem() Value { 584 k := v.kind() 585 switch k { 586 case Interface: 587 var eface interface{} 588 if v.typ.NumMethod() == 0 { 589 eface = *(*interface{})(v.ptr) 590 } else { 591 eface = (interface{})(*(*interface { 592 M() 593 })(v.ptr)) 594 } 595 x := unpackEface(eface) 596 if x.flag != 0 { 597 x.flag |= v.flag.ro() 598 } 599 return x 600 case Ptr: 601 ptr := v.ptr 602 if v.flag&flagIndir != 0 { 603 ptr = *(*unsafe.Pointer)(ptr) 604 } 605 // The returned value's address is v's value. 606 if ptr == nil { 607 return Value{} 608 } 609 tt := (*ptrType)(unsafe.Pointer(v.typ)) 610 typ := tt.elem 611 fl := v.flag&flagRO | flagIndir | flagAddr 612 fl |= flag(typ.Kind()) 613 return Value{typ, ptr, fl} 614 } 615 panic(&ValueError{"reflect.Value.Elem", v.kind()}) 616} 617 618// Field returns the i'th field of the struct v. 619// It panics if v's Kind is not Struct or i is out of range. 620func (v Value) Field(i int) Value { 621 if v.kind() != Struct { 622 panic(&ValueError{"reflect.Value.Field", v.kind()}) 623 } 624 tt := (*structType)(unsafe.Pointer(v.typ)) 625 if uint(i) >= uint(len(tt.fields)) { 626 panic("reflect: Field index out of range") 627 } 628 field := &tt.fields[i] 629 typ := field.typ 630 631 // Inherit permission bits from v, but clear flagEmbedRO. 632 fl := v.flag&(flagStickyRO|flagIndir|flagAddr) | flag(typ.Kind()) 633 // Using an unexported field forces flagRO. 634 if field.pkgPath != nil { 635 if field.anon() { 636 fl |= flagEmbedRO 637 } else { 638 fl |= flagStickyRO 639 } 640 } 641 // Either flagIndir is set and v.ptr points at struct, 642 // or flagIndir is not set and v.ptr is the actual struct data. 643 // In the former case, we want v.ptr + offset. 644 // In the latter case, we must have field.offset = 0, 645 // so v.ptr + field.offset is still the correct address. 646 ptr := add(v.ptr, field.offset(), "same as non-reflect &v.field") 647 return Value{typ, ptr, fl} 648} 649 650// FieldByIndex returns the nested field corresponding to index. 651// It panics if v's Kind is not struct. 652func (v Value) FieldByIndex(index []int) Value { 653 if len(index) == 1 { 654 return v.Field(index[0]) 655 } 656 v.mustBe(Struct) 657 for i, x := range index { 658 if i > 0 { 659 if v.Kind() == Ptr && v.typ.Elem().Kind() == Struct { 660 if v.IsNil() { 661 panic("reflect: indirection through nil pointer to embedded struct") 662 } 663 v = v.Elem() 664 } 665 } 666 v = v.Field(x) 667 } 668 return v 669} 670 671// FieldByName returns the struct field with the given name. 672// It returns the zero Value if no field was found. 673// It panics if v's Kind is not struct. 674func (v Value) FieldByName(name string) Value { 675 v.mustBe(Struct) 676 if f, ok := v.typ.FieldByName(name); ok { 677 return v.FieldByIndex(f.Index) 678 } 679 return Value{} 680} 681 682// FieldByNameFunc returns the struct field with a name 683// that satisfies the match function. 684// It panics if v's Kind is not struct. 685// It returns the zero Value if no field was found. 686func (v Value) FieldByNameFunc(match func(string) bool) Value { 687 if f, ok := v.typ.FieldByNameFunc(match); ok { 688 return v.FieldByIndex(f.Index) 689 } 690 return Value{} 691} 692 693// Float returns v's underlying value, as a float64. 694// It panics if v's Kind is not Float32 or Float64 695func (v Value) Float() float64 { 696 k := v.kind() 697 switch k { 698 case Float32: 699 return float64(*(*float32)(v.ptr)) 700 case Float64: 701 return *(*float64)(v.ptr) 702 } 703 panic(&ValueError{"reflect.Value.Float", v.kind()}) 704} 705 706var uint8Type = TypeOf(uint8(0)).(*rtype) 707 708// Index returns v's i'th element. 709// It panics if v's Kind is not Array, Slice, or String or i is out of range. 710func (v Value) Index(i int) Value { 711 switch v.kind() { 712 case Array: 713 tt := (*arrayType)(unsafe.Pointer(v.typ)) 714 if uint(i) >= uint(tt.len) { 715 panic("reflect: array index out of range") 716 } 717 typ := tt.elem 718 offset := uintptr(i) * typ.size 719 720 // Either flagIndir is set and v.ptr points at array, 721 // or flagIndir is not set and v.ptr is the actual array data. 722 // In the former case, we want v.ptr + offset. 723 // In the latter case, we must be doing Index(0), so offset = 0, 724 // so v.ptr + offset is still the correct address. 725 val := add(v.ptr, offset, "same as &v[i], i < tt.len") 726 fl := v.flag&(flagIndir|flagAddr) | v.flag.ro() | flag(typ.Kind()) // bits same as overall array 727 return Value{typ, val, fl} 728 729 case Slice: 730 // Element flag same as Elem of Ptr. 731 // Addressable, indirect, possibly read-only. 732 s := (*sliceHeader)(v.ptr) 733 if uint(i) >= uint(s.Len) { 734 panic("reflect: slice index out of range") 735 } 736 tt := (*sliceType)(unsafe.Pointer(v.typ)) 737 typ := tt.elem 738 val := arrayAt(s.Data, i, typ.size, "i < s.Len") 739 fl := flagAddr | flagIndir | v.flag.ro() | flag(typ.Kind()) 740 return Value{typ, val, fl} 741 742 case String: 743 s := (*stringHeader)(v.ptr) 744 if uint(i) >= uint(s.Len) { 745 panic("reflect: string index out of range") 746 } 747 p := arrayAt(s.Data, i, 1, "i < s.Len") 748 fl := v.flag.ro() | flag(Uint8) | flagIndir 749 return Value{uint8Type, p, fl} 750 } 751 panic(&ValueError{"reflect.Value.Index", v.kind()}) 752} 753 754// Int returns v's underlying value, as an int64. 755// It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64. 756func (v Value) Int() int64 { 757 k := v.kind() 758 p := v.ptr 759 switch k { 760 case Int: 761 return int64(*(*int)(p)) 762 case Int8: 763 return int64(*(*int8)(p)) 764 case Int16: 765 return int64(*(*int16)(p)) 766 case Int32: 767 return int64(*(*int32)(p)) 768 case Int64: 769 return *(*int64)(p) 770 } 771 panic(&ValueError{"reflect.Value.Int", v.kind()}) 772} 773 774// CanInterface reports whether Interface can be used without panicking. 775func (v Value) CanInterface() bool { 776 if v.flag == 0 { 777 panic(&ValueError{"reflect.Value.CanInterface", Invalid}) 778 } 779 return v.flag&flagRO == 0 780} 781 782// Interface returns v's current value as an interface{}. 783// It is equivalent to: 784// var i interface{} = (v's underlying value) 785// It panics if the Value was obtained by accessing 786// unexported struct fields. 787func (v Value) Interface() (i interface{}) { 788 return valueInterface(v, true) 789} 790 791func valueInterface(v Value, safe bool) interface{} { 792 if v.flag == 0 { 793 panic(&ValueError{"reflect.Value.Interface", 0}) 794 } 795 if safe && v.flag&flagRO != 0 { 796 // Do not allow access to unexported values via Interface, 797 // because they might be pointers that should not be 798 // writable or methods or function that should not be callable. 799 panic("reflect.Value.Interface: cannot return value obtained from unexported field or method") 800 } 801 if v.flag&flagMethod != 0 { 802 v = makeMethodValue("Interface", v) 803 } 804 805 if v.flag&flagMethodFn != 0 { 806 if v.typ.Kind() != Func { 807 panic("reflect: MethodFn of non-Func") 808 } 809 ft := (*funcType)(unsafe.Pointer(v.typ)) 810 if ft.in[0].Kind() != Ptr { 811 v = makeValueMethod(v) 812 } 813 } 814 815 if v.kind() == Interface { 816 // Special case: return the element inside the interface. 817 // Empty interface has one layout, all interfaces with 818 // methods have a second layout. 819 if v.NumMethod() == 0 { 820 return *(*interface{})(v.ptr) 821 } 822 return *(*interface { 823 M() 824 })(v.ptr) 825 } 826 827 // TODO: pass safe to packEface so we don't need to copy if safe==true? 828 return packEface(v) 829} 830 831// InterfaceData returns the interface v's value as a uintptr pair. 832// It panics if v's Kind is not Interface. 833func (v Value) InterfaceData() [2]uintptr { 834 // TODO: deprecate this 835 v.mustBe(Interface) 836 // We treat this as a read operation, so we allow 837 // it even for unexported data, because the caller 838 // has to import "unsafe" to turn it into something 839 // that can be abused. 840 // Interface value is always bigger than a word; assume flagIndir. 841 return *(*[2]uintptr)(v.ptr) 842} 843 844// IsNil reports whether its argument v is nil. The argument must be 845// a chan, func, interface, map, pointer, or slice value; if it is 846// not, IsNil panics. Note that IsNil is not always equivalent to a 847// regular comparison with nil in Go. For example, if v was created 848// by calling ValueOf with an uninitialized interface variable i, 849// i==nil will be true but v.IsNil will panic as v will be the zero 850// Value. 851func (v Value) IsNil() bool { 852 k := v.kind() 853 switch k { 854 case Chan, Func, Map, Ptr: 855 if v.flag&flagMethod != 0 { 856 return false 857 } 858 ptr := v.ptr 859 if v.flag&flagIndir != 0 { 860 ptr = *(*unsafe.Pointer)(ptr) 861 } 862 return ptr == nil 863 case Interface, Slice: 864 // Both interface and slice are nil if first word is 0. 865 // Both are always bigger than a word; assume flagIndir. 866 return *(*unsafe.Pointer)(v.ptr) == nil 867 } 868 panic(&ValueError{"reflect.Value.IsNil", v.kind()}) 869} 870 871// IsValid reports whether v represents a value. 872// It returns false if v is the zero Value. 873// If IsValid returns false, all other methods except String panic. 874// Most functions and methods never return an invalid value. 875// If one does, its documentation states the conditions explicitly. 876func (v Value) IsValid() bool { 877 return v.flag != 0 878} 879 880// Kind returns v's Kind. 881// If v is the zero Value (IsValid returns false), Kind returns Invalid. 882func (v Value) Kind() Kind { 883 return v.kind() 884} 885 886// Len returns v's length. 887// It panics if v's Kind is not Array, Chan, Map, Slice, or String. 888func (v Value) Len() int { 889 k := v.kind() 890 switch k { 891 case Array: 892 tt := (*arrayType)(unsafe.Pointer(v.typ)) 893 return int(tt.len) 894 case Chan: 895 return chanlen(v.pointer()) 896 case Map: 897 return maplen(v.pointer()) 898 case Slice: 899 // Slice is bigger than a word; assume flagIndir. 900 return (*sliceHeader)(v.ptr).Len 901 case String: 902 // String is bigger than a word; assume flagIndir. 903 return (*stringHeader)(v.ptr).Len 904 } 905 panic(&ValueError{"reflect.Value.Len", v.kind()}) 906} 907 908// MapIndex returns the value associated with key in the map v. 909// It panics if v's Kind is not Map. 910// It returns the zero Value if key is not found in the map or if v represents a nil map. 911// As in Go, the key's value must be assignable to the map's key type. 912func (v Value) MapIndex(key Value) Value { 913 v.mustBe(Map) 914 tt := (*mapType)(unsafe.Pointer(v.typ)) 915 916 // Do not require key to be exported, so that DeepEqual 917 // and other programs can use all the keys returned by 918 // MapKeys as arguments to MapIndex. If either the map 919 // or the key is unexported, though, the result will be 920 // considered unexported. This is consistent with the 921 // behavior for structs, which allow read but not write 922 // of unexported fields. 923 key = key.assignTo("reflect.Value.MapIndex", tt.key, nil) 924 925 var k unsafe.Pointer 926 if key.flag&flagIndir != 0 { 927 k = key.ptr 928 } else { 929 k = unsafe.Pointer(&key.ptr) 930 } 931 e := mapaccess(v.typ, v.pointer(), k) 932 if e == nil { 933 return Value{} 934 } 935 typ := tt.elem 936 fl := (v.flag | key.flag).ro() 937 fl |= flag(typ.Kind()) 938 if !ifaceIndir(typ) { 939 return Value{typ, *(*unsafe.Pointer)(e), fl} 940 } 941 // Copy result so future changes to the map 942 // won't change the underlying value. 943 c := unsafe_New(typ) 944 typedmemmove(typ, c, e) 945 return Value{typ, c, fl | flagIndir} 946} 947 948// MapKeys returns a slice containing all the keys present in the map, 949// in unspecified order. 950// It panics if v's Kind is not Map. 951// It returns an empty slice if v represents a nil map. 952func (v Value) MapKeys() []Value { 953 v.mustBe(Map) 954 tt := (*mapType)(unsafe.Pointer(v.typ)) 955 keyType := tt.key 956 957 fl := v.flag.ro() | flag(keyType.Kind()) 958 959 m := v.pointer() 960 mlen := int(0) 961 if m != nil { 962 mlen = maplen(m) 963 } 964 it := mapiterinit(v.typ, m) 965 a := make([]Value, mlen) 966 var i int 967 for i = 0; i < len(a); i++ { 968 key := mapiterkey(it) 969 if key == nil { 970 // Someone deleted an entry from the map since we 971 // called maplen above. It's a data race, but nothing 972 // we can do about it. 973 break 974 } 975 if ifaceIndir(keyType) { 976 // Copy result so future changes to the map 977 // won't change the underlying value. 978 c := unsafe_New(keyType) 979 typedmemmove(keyType, c, key) 980 a[i] = Value{keyType, c, fl | flagIndir} 981 } else { 982 a[i] = Value{keyType, *(*unsafe.Pointer)(key), fl} 983 } 984 mapiternext(it) 985 } 986 return a[:i] 987} 988 989// Method returns a function value corresponding to v's i'th method. 990// The arguments to a Call on the returned function should not include 991// a receiver; the returned function will always use v as the receiver. 992// Method panics if i is out of range or if v is a nil interface value. 993func (v Value) Method(i int) Value { 994 if v.typ == nil { 995 panic(&ValueError{"reflect.Value.Method", Invalid}) 996 } 997 if v.flag&flagMethod != 0 || uint(i) >= uint(v.typ.NumMethod()) { 998 panic("reflect: Method index out of range") 999 } 1000 if v.typ.Kind() == Interface && v.IsNil() { 1001 panic("reflect: Method on nil interface value") 1002 } 1003 fl := v.flag & (flagStickyRO | flagIndir) // Clear flagEmbedRO 1004 fl |= flag(Func) 1005 fl |= flag(i)<<flagMethodShift | flagMethod 1006 return Value{v.typ, v.ptr, fl} 1007} 1008 1009// NumMethod returns the number of exported methods in the value's method set. 1010func (v Value) NumMethod() int { 1011 if v.typ == nil { 1012 panic(&ValueError{"reflect.Value.NumMethod", Invalid}) 1013 } 1014 if v.flag&flagMethod != 0 { 1015 return 0 1016 } 1017 return v.typ.NumMethod() 1018} 1019 1020// MethodByName returns a function value corresponding to the method 1021// of v with the given name. 1022// The arguments to a Call on the returned function should not include 1023// a receiver; the returned function will always use v as the receiver. 1024// It returns the zero Value if no method was found. 1025func (v Value) MethodByName(name string) Value { 1026 if v.typ == nil { 1027 panic(&ValueError{"reflect.Value.MethodByName", Invalid}) 1028 } 1029 if v.flag&flagMethod != 0 { 1030 return Value{} 1031 } 1032 m, ok := v.typ.MethodByName(name) 1033 if !ok { 1034 return Value{} 1035 } 1036 return v.Method(m.Index) 1037} 1038 1039// NumField returns the number of fields in the struct v. 1040// It panics if v's Kind is not Struct. 1041func (v Value) NumField() int { 1042 v.mustBe(Struct) 1043 tt := (*structType)(unsafe.Pointer(v.typ)) 1044 return len(tt.fields) 1045} 1046 1047// OverflowComplex reports whether the complex128 x cannot be represented by v's type. 1048// It panics if v's Kind is not Complex64 or Complex128. 1049func (v Value) OverflowComplex(x complex128) bool { 1050 k := v.kind() 1051 switch k { 1052 case Complex64: 1053 return overflowFloat32(real(x)) || overflowFloat32(imag(x)) 1054 case Complex128: 1055 return false 1056 } 1057 panic(&ValueError{"reflect.Value.OverflowComplex", v.kind()}) 1058} 1059 1060// OverflowFloat reports whether the float64 x cannot be represented by v's type. 1061// It panics if v's Kind is not Float32 or Float64. 1062func (v Value) OverflowFloat(x float64) bool { 1063 k := v.kind() 1064 switch k { 1065 case Float32: 1066 return overflowFloat32(x) 1067 case Float64: 1068 return false 1069 } 1070 panic(&ValueError{"reflect.Value.OverflowFloat", v.kind()}) 1071} 1072 1073func overflowFloat32(x float64) bool { 1074 if x < 0 { 1075 x = -x 1076 } 1077 return math.MaxFloat32 < x && x <= math.MaxFloat64 1078} 1079 1080// OverflowInt reports whether the int64 x cannot be represented by v's type. 1081// It panics if v's Kind is not Int, Int8, int16, Int32, or Int64. 1082func (v Value) OverflowInt(x int64) bool { 1083 k := v.kind() 1084 switch k { 1085 case Int, Int8, Int16, Int32, Int64: 1086 bitSize := v.typ.size * 8 1087 trunc := (x << (64 - bitSize)) >> (64 - bitSize) 1088 return x != trunc 1089 } 1090 panic(&ValueError{"reflect.Value.OverflowInt", v.kind()}) 1091} 1092 1093// OverflowUint reports whether the uint64 x cannot be represented by v's type. 1094// It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64. 1095func (v Value) OverflowUint(x uint64) bool { 1096 k := v.kind() 1097 switch k { 1098 case Uint, Uintptr, Uint8, Uint16, Uint32, Uint64: 1099 bitSize := v.typ.size * 8 1100 trunc := (x << (64 - bitSize)) >> (64 - bitSize) 1101 return x != trunc 1102 } 1103 panic(&ValueError{"reflect.Value.OverflowUint", v.kind()}) 1104} 1105 1106// Pointer returns v's value as a uintptr. 1107// It returns uintptr instead of unsafe.Pointer so that 1108// code using reflect cannot obtain unsafe.Pointers 1109// without importing the unsafe package explicitly. 1110// It panics if v's Kind is not Chan, Func, Map, Ptr, Slice, or UnsafePointer. 1111// 1112// If v's Kind is Func, the returned pointer is an underlying 1113// code pointer, but not necessarily enough to identify a 1114// single function uniquely. The only guarantee is that the 1115// result is zero if and only if v is a nil func Value. 1116// 1117// If v's Kind is Slice, the returned pointer is to the first 1118// element of the slice. If the slice is nil the returned value 1119// is 0. If the slice is empty but non-nil the return value is non-zero. 1120func (v Value) Pointer() uintptr { 1121 // TODO: deprecate 1122 k := v.kind() 1123 switch k { 1124 case Chan, Map, Ptr, UnsafePointer: 1125 return uintptr(v.pointer()) 1126 case Func: 1127 p := v.pointer() 1128 // Non-nil func value points at data block. 1129 // First word of data block is actual code. 1130 if p != nil { 1131 p = *(*unsafe.Pointer)(p) 1132 } 1133 return uintptr(p) 1134 1135 case Slice: 1136 return (*SliceHeader)(v.ptr).Data 1137 } 1138 panic(&ValueError{"reflect.Value.Pointer", v.kind()}) 1139} 1140 1141// Recv receives and returns a value from the channel v. 1142// It panics if v's Kind is not Chan. 1143// The receive blocks until a value is ready. 1144// The boolean value ok is true if the value x corresponds to a send 1145// on the channel, false if it is a zero value received because the channel is closed. 1146func (v Value) Recv() (x Value, ok bool) { 1147 v.mustBe(Chan) 1148 v.mustBeExported() 1149 return v.recv(false) 1150} 1151 1152// internal recv, possibly non-blocking (nb). 1153// v is known to be a channel. 1154func (v Value) recv(nb bool) (val Value, ok bool) { 1155 tt := (*chanType)(unsafe.Pointer(v.typ)) 1156 if ChanDir(tt.dir)&RecvDir == 0 { 1157 panic("reflect: recv on send-only channel") 1158 } 1159 t := tt.elem 1160 val = Value{t, nil, flag(t.Kind())} 1161 var p unsafe.Pointer 1162 if ifaceIndir(t) { 1163 p = unsafe_New(t) 1164 val.ptr = p 1165 val.flag |= flagIndir 1166 } else { 1167 p = unsafe.Pointer(&val.ptr) 1168 } 1169 selected, ok := chanrecv(v.pointer(), nb, p) 1170 if !selected { 1171 val = Value{} 1172 } 1173 return 1174} 1175 1176// Send sends x on the channel v. 1177// It panics if v's kind is not Chan or if x's type is not the same type as v's element type. 1178// As in Go, x's value must be assignable to the channel's element type. 1179func (v Value) Send(x Value) { 1180 v.mustBe(Chan) 1181 v.mustBeExported() 1182 v.send(x, false) 1183} 1184 1185// internal send, possibly non-blocking. 1186// v is known to be a channel. 1187func (v Value) send(x Value, nb bool) (selected bool) { 1188 tt := (*chanType)(unsafe.Pointer(v.typ)) 1189 if ChanDir(tt.dir)&SendDir == 0 { 1190 panic("reflect: send on recv-only channel") 1191 } 1192 x.mustBeExported() 1193 x = x.assignTo("reflect.Value.Send", tt.elem, nil) 1194 var p unsafe.Pointer 1195 if x.flag&flagIndir != 0 { 1196 p = x.ptr 1197 } else { 1198 p = unsafe.Pointer(&x.ptr) 1199 } 1200 return chansend(v.pointer(), p, nb) 1201} 1202 1203// Set assigns x to the value v. 1204// It panics if CanSet returns false. 1205// As in Go, x's value must be assignable to v's type. 1206func (v Value) Set(x Value) { 1207 v.mustBeAssignable() 1208 x.mustBeExported() // do not let unexported x leak 1209 var target unsafe.Pointer 1210 if v.kind() == Interface { 1211 target = v.ptr 1212 } 1213 x = x.assignTo("reflect.Set", v.typ, target) 1214 if x.flag&flagIndir != 0 { 1215 typedmemmove(v.typ, v.ptr, x.ptr) 1216 } else { 1217 *(*unsafe.Pointer)(v.ptr) = x.ptr 1218 } 1219} 1220 1221// SetBool sets v's underlying value. 1222// It panics if v's Kind is not Bool or if CanSet() is false. 1223func (v Value) SetBool(x bool) { 1224 v.mustBeAssignable() 1225 v.mustBe(Bool) 1226 *(*bool)(v.ptr) = x 1227} 1228 1229// SetBytes sets v's underlying value. 1230// It panics if v's underlying value is not a slice of bytes. 1231func (v Value) SetBytes(x []byte) { 1232 v.mustBeAssignable() 1233 v.mustBe(Slice) 1234 if v.typ.Elem().Kind() != Uint8 { 1235 panic("reflect.Value.SetBytes of non-byte slice") 1236 } 1237 *(*[]byte)(v.ptr) = x 1238} 1239 1240// setRunes sets v's underlying value. 1241// It panics if v's underlying value is not a slice of runes (int32s). 1242func (v Value) setRunes(x []rune) { 1243 v.mustBeAssignable() 1244 v.mustBe(Slice) 1245 if v.typ.Elem().Kind() != Int32 { 1246 panic("reflect.Value.setRunes of non-rune slice") 1247 } 1248 *(*[]rune)(v.ptr) = x 1249} 1250 1251// SetComplex sets v's underlying value to x. 1252// It panics if v's Kind is not Complex64 or Complex128, or if CanSet() is false. 1253func (v Value) SetComplex(x complex128) { 1254 v.mustBeAssignable() 1255 switch k := v.kind(); k { 1256 default: 1257 panic(&ValueError{"reflect.Value.SetComplex", v.kind()}) 1258 case Complex64: 1259 *(*complex64)(v.ptr) = complex64(x) 1260 case Complex128: 1261 *(*complex128)(v.ptr) = x 1262 } 1263} 1264 1265// SetFloat sets v's underlying value to x. 1266// It panics if v's Kind is not Float32 or Float64, or if CanSet() is false. 1267func (v Value) SetFloat(x float64) { 1268 v.mustBeAssignable() 1269 switch k := v.kind(); k { 1270 default: 1271 panic(&ValueError{"reflect.Value.SetFloat", v.kind()}) 1272 case Float32: 1273 *(*float32)(v.ptr) = float32(x) 1274 case Float64: 1275 *(*float64)(v.ptr) = x 1276 } 1277} 1278 1279// SetInt sets v's underlying value to x. 1280// It panics if v's Kind is not Int, Int8, Int16, Int32, or Int64, or if CanSet() is false. 1281func (v Value) SetInt(x int64) { 1282 v.mustBeAssignable() 1283 switch k := v.kind(); k { 1284 default: 1285 panic(&ValueError{"reflect.Value.SetInt", v.kind()}) 1286 case Int: 1287 *(*int)(v.ptr) = int(x) 1288 case Int8: 1289 *(*int8)(v.ptr) = int8(x) 1290 case Int16: 1291 *(*int16)(v.ptr) = int16(x) 1292 case Int32: 1293 *(*int32)(v.ptr) = int32(x) 1294 case Int64: 1295 *(*int64)(v.ptr) = x 1296 } 1297} 1298 1299// SetLen sets v's length to n. 1300// It panics if v's Kind is not Slice or if n is negative or 1301// greater than the capacity of the slice. 1302func (v Value) SetLen(n int) { 1303 v.mustBeAssignable() 1304 v.mustBe(Slice) 1305 s := (*sliceHeader)(v.ptr) 1306 if uint(n) > uint(s.Cap) { 1307 panic("reflect: slice length out of range in SetLen") 1308 } 1309 s.Len = n 1310} 1311 1312// SetCap sets v's capacity to n. 1313// It panics if v's Kind is not Slice or if n is smaller than the length or 1314// greater than the capacity of the slice. 1315func (v Value) SetCap(n int) { 1316 v.mustBeAssignable() 1317 v.mustBe(Slice) 1318 s := (*sliceHeader)(v.ptr) 1319 if n < s.Len || n > s.Cap { 1320 panic("reflect: slice capacity out of range in SetCap") 1321 } 1322 s.Cap = n 1323} 1324 1325// SetMapIndex sets the value associated with key in the map v to val. 1326// It panics if v's Kind is not Map. 1327// If val is the zero Value, SetMapIndex deletes the key from the map. 1328// Otherwise if v holds a nil map, SetMapIndex will panic. 1329// As in Go, key's value must be assignable to the map's key type, 1330// and val's value must be assignable to the map's value type. 1331func (v Value) SetMapIndex(key, val Value) { 1332 v.mustBe(Map) 1333 v.mustBeExported() 1334 key.mustBeExported() 1335 tt := (*mapType)(unsafe.Pointer(v.typ)) 1336 key = key.assignTo("reflect.Value.SetMapIndex", tt.key, nil) 1337 var k unsafe.Pointer 1338 if key.flag&flagIndir != 0 { 1339 k = key.ptr 1340 } else { 1341 k = unsafe.Pointer(&key.ptr) 1342 } 1343 if val.typ == nil { 1344 mapdelete(v.typ, v.pointer(), k) 1345 return 1346 } 1347 val.mustBeExported() 1348 val = val.assignTo("reflect.Value.SetMapIndex", tt.elem, nil) 1349 var e unsafe.Pointer 1350 if val.flag&flagIndir != 0 { 1351 e = val.ptr 1352 } else { 1353 e = unsafe.Pointer(&val.ptr) 1354 } 1355 mapassign(v.typ, v.pointer(), k, e) 1356} 1357 1358// SetUint sets v's underlying value to x. 1359// It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64, or if CanSet() is false. 1360func (v Value) SetUint(x uint64) { 1361 v.mustBeAssignable() 1362 switch k := v.kind(); k { 1363 default: 1364 panic(&ValueError{"reflect.Value.SetUint", v.kind()}) 1365 case Uint: 1366 *(*uint)(v.ptr) = uint(x) 1367 case Uint8: 1368 *(*uint8)(v.ptr) = uint8(x) 1369 case Uint16: 1370 *(*uint16)(v.ptr) = uint16(x) 1371 case Uint32: 1372 *(*uint32)(v.ptr) = uint32(x) 1373 case Uint64: 1374 *(*uint64)(v.ptr) = x 1375 case Uintptr: 1376 *(*uintptr)(v.ptr) = uintptr(x) 1377 } 1378} 1379 1380// SetPointer sets the unsafe.Pointer value v to x. 1381// It panics if v's Kind is not UnsafePointer. 1382func (v Value) SetPointer(x unsafe.Pointer) { 1383 v.mustBeAssignable() 1384 v.mustBe(UnsafePointer) 1385 *(*unsafe.Pointer)(v.ptr) = x 1386} 1387 1388// SetString sets v's underlying value to x. 1389// It panics if v's Kind is not String or if CanSet() is false. 1390func (v Value) SetString(x string) { 1391 v.mustBeAssignable() 1392 v.mustBe(String) 1393 *(*string)(v.ptr) = x 1394} 1395 1396// Slice returns v[i:j]. 1397// It panics if v's Kind is not Array, Slice or String, or if v is an unaddressable array, 1398// or if the indexes are out of bounds. 1399func (v Value) Slice(i, j int) Value { 1400 var ( 1401 cap int 1402 typ *sliceType 1403 base unsafe.Pointer 1404 ) 1405 switch kind := v.kind(); kind { 1406 default: 1407 panic(&ValueError{"reflect.Value.Slice", v.kind()}) 1408 1409 case Array: 1410 if v.flag&flagAddr == 0 { 1411 panic("reflect.Value.Slice: slice of unaddressable array") 1412 } 1413 tt := (*arrayType)(unsafe.Pointer(v.typ)) 1414 cap = int(tt.len) 1415 typ = (*sliceType)(unsafe.Pointer(tt.slice)) 1416 base = v.ptr 1417 1418 case Slice: 1419 typ = (*sliceType)(unsafe.Pointer(v.typ)) 1420 s := (*sliceHeader)(v.ptr) 1421 base = s.Data 1422 cap = s.Cap 1423 1424 case String: 1425 s := (*stringHeader)(v.ptr) 1426 if i < 0 || j < i || j > s.Len { 1427 panic("reflect.Value.Slice: string slice index out of bounds") 1428 } 1429 var t stringHeader 1430 if i < s.Len { 1431 t = stringHeader{arrayAt(s.Data, i, 1, "i < s.Len"), j - i} 1432 } 1433 return Value{v.typ, unsafe.Pointer(&t), v.flag} 1434 } 1435 1436 if i < 0 || j < i || j > cap { 1437 panic("reflect.Value.Slice: slice index out of bounds") 1438 } 1439 1440 // Declare slice so that gc can see the base pointer in it. 1441 var x []unsafe.Pointer 1442 1443 // Reinterpret as *sliceHeader to edit. 1444 s := (*sliceHeader)(unsafe.Pointer(&x)) 1445 s.Len = j - i 1446 s.Cap = cap - i 1447 if cap-i > 0 { 1448 s.Data = arrayAt(base, i, typ.elem.Size(), "i < cap") 1449 } else { 1450 // do not advance pointer, to avoid pointing beyond end of slice 1451 s.Data = base 1452 } 1453 1454 fl := v.flag.ro() | flagIndir | flag(Slice) 1455 return Value{typ.common(), unsafe.Pointer(&x), fl} 1456} 1457 1458// Slice3 is the 3-index form of the slice operation: it returns v[i:j:k]. 1459// It panics if v's Kind is not Array or Slice, or if v is an unaddressable array, 1460// or if the indexes are out of bounds. 1461func (v Value) Slice3(i, j, k int) Value { 1462 var ( 1463 cap int 1464 typ *sliceType 1465 base unsafe.Pointer 1466 ) 1467 switch kind := v.kind(); kind { 1468 default: 1469 panic(&ValueError{"reflect.Value.Slice3", v.kind()}) 1470 1471 case Array: 1472 if v.flag&flagAddr == 0 { 1473 panic("reflect.Value.Slice3: slice of unaddressable array") 1474 } 1475 tt := (*arrayType)(unsafe.Pointer(v.typ)) 1476 cap = int(tt.len) 1477 typ = (*sliceType)(unsafe.Pointer(tt.slice)) 1478 base = v.ptr 1479 1480 case Slice: 1481 typ = (*sliceType)(unsafe.Pointer(v.typ)) 1482 s := (*sliceHeader)(v.ptr) 1483 base = s.Data 1484 cap = s.Cap 1485 } 1486 1487 if i < 0 || j < i || k < j || k > cap { 1488 panic("reflect.Value.Slice3: slice index out of bounds") 1489 } 1490 1491 // Declare slice so that the garbage collector 1492 // can see the base pointer in it. 1493 var x []unsafe.Pointer 1494 1495 // Reinterpret as *sliceHeader to edit. 1496 s := (*sliceHeader)(unsafe.Pointer(&x)) 1497 s.Len = j - i 1498 s.Cap = k - i 1499 if k-i > 0 { 1500 s.Data = arrayAt(base, i, typ.elem.Size(), "i < k <= cap") 1501 } else { 1502 // do not advance pointer, to avoid pointing beyond end of slice 1503 s.Data = base 1504 } 1505 1506 fl := v.flag.ro() | flagIndir | flag(Slice) 1507 return Value{typ.common(), unsafe.Pointer(&x), fl} 1508} 1509 1510// String returns the string v's underlying value, as a string. 1511// String is a special case because of Go's String method convention. 1512// Unlike the other getters, it does not panic if v's Kind is not String. 1513// Instead, it returns a string of the form "<T value>" where T is v's type. 1514// The fmt package treats Values specially. It does not call their String 1515// method implicitly but instead prints the concrete values they hold. 1516func (v Value) String() string { 1517 switch k := v.kind(); k { 1518 case Invalid: 1519 return "<invalid Value>" 1520 case String: 1521 return *(*string)(v.ptr) 1522 } 1523 // If you call String on a reflect.Value of other type, it's better to 1524 // print something than to panic. Useful in debugging. 1525 return "<" + v.Type().String() + " Value>" 1526} 1527 1528// TryRecv attempts to receive a value from the channel v but will not block. 1529// It panics if v's Kind is not Chan. 1530// If the receive delivers a value, x is the transferred value and ok is true. 1531// If the receive cannot finish without blocking, x is the zero Value and ok is false. 1532// If the channel is closed, x is the zero value for the channel's element type and ok is false. 1533func (v Value) TryRecv() (x Value, ok bool) { 1534 v.mustBe(Chan) 1535 v.mustBeExported() 1536 return v.recv(true) 1537} 1538 1539// TrySend attempts to send x on the channel v but will not block. 1540// It panics if v's Kind is not Chan. 1541// It reports whether the value was sent. 1542// As in Go, x's value must be assignable to the channel's element type. 1543func (v Value) TrySend(x Value) bool { 1544 v.mustBe(Chan) 1545 v.mustBeExported() 1546 return v.send(x, true) 1547} 1548 1549// Type returns v's type. 1550func (v Value) Type() Type { 1551 f := v.flag 1552 if f == 0 { 1553 panic(&ValueError{"reflect.Value.Type", Invalid}) 1554 } 1555 if f&flagMethod == 0 { 1556 // Easy case 1557 return toType(v.typ) 1558 } 1559 1560 // Method value. 1561 // v.typ describes the receiver, not the method type. 1562 i := int(v.flag) >> flagMethodShift 1563 if v.typ.Kind() == Interface { 1564 // Method on interface. 1565 tt := (*interfaceType)(unsafe.Pointer(v.typ)) 1566 if uint(i) >= uint(len(tt.methods)) { 1567 panic("reflect: internal error: invalid method index") 1568 } 1569 m := &tt.methods[i] 1570 return toType(m.typ) 1571 } 1572 // Method on concrete type. 1573 ms := v.typ.exportedMethods() 1574 if uint(i) >= uint(len(ms)) { 1575 panic("reflect: internal error: invalid method index") 1576 } 1577 m := ms[i] 1578 return toType(m.mtyp) 1579} 1580 1581// Uint returns v's underlying value, as a uint64. 1582// It panics if v's Kind is not Uint, Uintptr, Uint8, Uint16, Uint32, or Uint64. 1583func (v Value) Uint() uint64 { 1584 k := v.kind() 1585 p := v.ptr 1586 switch k { 1587 case Uint: 1588 return uint64(*(*uint)(p)) 1589 case Uint8: 1590 return uint64(*(*uint8)(p)) 1591 case Uint16: 1592 return uint64(*(*uint16)(p)) 1593 case Uint32: 1594 return uint64(*(*uint32)(p)) 1595 case Uint64: 1596 return *(*uint64)(p) 1597 case Uintptr: 1598 return uint64(*(*uintptr)(p)) 1599 } 1600 panic(&ValueError{"reflect.Value.Uint", v.kind()}) 1601} 1602 1603// UnsafeAddr returns a pointer to v's data. 1604// It is for advanced clients that also import the "unsafe" package. 1605// It panics if v is not addressable. 1606func (v Value) UnsafeAddr() uintptr { 1607 // TODO: deprecate 1608 if v.typ == nil { 1609 panic(&ValueError{"reflect.Value.UnsafeAddr", Invalid}) 1610 } 1611 if v.flag&flagAddr == 0 { 1612 panic("reflect.Value.UnsafeAddr of unaddressable value") 1613 } 1614 return uintptr(v.ptr) 1615} 1616 1617// StringHeader is the runtime representation of a string. 1618// It cannot be used safely or portably and its representation may 1619// change in a later release. 1620// Moreover, the Data field is not sufficient to guarantee the data 1621// it references will not be garbage collected, so programs must keep 1622// a separate, correctly typed pointer to the underlying data. 1623type StringHeader struct { 1624 Data uintptr 1625 Len int 1626} 1627 1628// stringHeader is a safe version of StringHeader used within this package. 1629type stringHeader struct { 1630 Data unsafe.Pointer 1631 Len int 1632} 1633 1634// SliceHeader is the runtime representation of a slice. 1635// It cannot be used safely or portably and its representation may 1636// change in a later release. 1637// Moreover, the Data field is not sufficient to guarantee the data 1638// it references will not be garbage collected, so programs must keep 1639// a separate, correctly typed pointer to the underlying data. 1640type SliceHeader struct { 1641 Data uintptr 1642 Len int 1643 Cap int 1644} 1645 1646// sliceHeader is a safe version of SliceHeader used within this package. 1647type sliceHeader struct { 1648 Data unsafe.Pointer 1649 Len int 1650 Cap int 1651} 1652 1653func typesMustMatch(what string, t1, t2 Type) { 1654 if t1 != t2 { 1655 panic(what + ": " + t1.String() + " != " + t2.String()) 1656 } 1657} 1658 1659// arrayAt returns the i-th element of p, 1660// an array whose elements are eltSize bytes wide. 1661// The array pointed at by p must have at least i+1 elements: 1662// it is invalid (but impossible to check here) to pass i >= len, 1663// because then the result will point outside the array. 1664// whySafe must explain why i < len. (Passing "i < len" is fine; 1665// the benefit is to surface this assumption at the call site.) 1666func arrayAt(p unsafe.Pointer, i int, eltSize uintptr, whySafe string) unsafe.Pointer { 1667 return add(p, uintptr(i)*eltSize, "i < len") 1668} 1669 1670// grow grows the slice s so that it can hold extra more values, allocating 1671// more capacity if needed. It also returns the old and new slice lengths. 1672func grow(s Value, extra int) (Value, int, int) { 1673 i0 := s.Len() 1674 i1 := i0 + extra 1675 if i1 < i0 { 1676 panic("reflect.Append: slice overflow") 1677 } 1678 m := s.Cap() 1679 if i1 <= m { 1680 return s.Slice(0, i1), i0, i1 1681 } 1682 if m == 0 { 1683 m = extra 1684 } else { 1685 for m < i1 { 1686 if i0 < 1024 { 1687 m += m 1688 } else { 1689 m += m / 4 1690 } 1691 } 1692 } 1693 t := MakeSlice(s.Type(), i1, m) 1694 Copy(t, s) 1695 return t, i0, i1 1696} 1697 1698// Append appends the values x to a slice s and returns the resulting slice. 1699// As in Go, each x's value must be assignable to the slice's element type. 1700func Append(s Value, x ...Value) Value { 1701 s.mustBe(Slice) 1702 s, i0, i1 := grow(s, len(x)) 1703 for i, j := i0, 0; i < i1; i, j = i+1, j+1 { 1704 s.Index(i).Set(x[j]) 1705 } 1706 return s 1707} 1708 1709// AppendSlice appends a slice t to a slice s and returns the resulting slice. 1710// The slices s and t must have the same element type. 1711func AppendSlice(s, t Value) Value { 1712 s.mustBe(Slice) 1713 t.mustBe(Slice) 1714 typesMustMatch("reflect.AppendSlice", s.Type().Elem(), t.Type().Elem()) 1715 s, i0, i1 := grow(s, t.Len()) 1716 Copy(s.Slice(i0, i1), t) 1717 return s 1718} 1719 1720// Copy copies the contents of src into dst until either 1721// dst has been filled or src has been exhausted. 1722// It returns the number of elements copied. 1723// Dst and src each must have kind Slice or Array, and 1724// dst and src must have the same element type. 1725// 1726// As a special case, src can have kind String if the element type of dst is kind Uint8. 1727func Copy(dst, src Value) int { 1728 dk := dst.kind() 1729 if dk != Array && dk != Slice { 1730 panic(&ValueError{"reflect.Copy", dk}) 1731 } 1732 if dk == Array { 1733 dst.mustBeAssignable() 1734 } 1735 dst.mustBeExported() 1736 1737 sk := src.kind() 1738 var stringCopy bool 1739 if sk != Array && sk != Slice { 1740 stringCopy = sk == String && dst.typ.Elem().Kind() == Uint8 1741 if !stringCopy { 1742 panic(&ValueError{"reflect.Copy", sk}) 1743 } 1744 } 1745 src.mustBeExported() 1746 1747 de := dst.typ.Elem() 1748 if !stringCopy { 1749 se := src.typ.Elem() 1750 typesMustMatch("reflect.Copy", de, se) 1751 } 1752 1753 var ds, ss sliceHeader 1754 if dk == Array { 1755 ds.Data = dst.ptr 1756 ds.Len = dst.Len() 1757 ds.Cap = ds.Len 1758 } else { 1759 ds = *(*sliceHeader)(dst.ptr) 1760 } 1761 if sk == Array { 1762 ss.Data = src.ptr 1763 ss.Len = src.Len() 1764 ss.Cap = ss.Len 1765 } else if sk == Slice { 1766 ss = *(*sliceHeader)(src.ptr) 1767 } else { 1768 sh := *(*stringHeader)(src.ptr) 1769 ss.Data = sh.Data 1770 ss.Len = sh.Len 1771 ss.Cap = sh.Len 1772 } 1773 1774 return typedslicecopy(de.common(), ds, ss) 1775} 1776 1777// A runtimeSelect is a single case passed to rselect. 1778// This must match ../runtime/select.go:/runtimeSelect 1779type runtimeSelect struct { 1780 dir SelectDir // SelectSend, SelectRecv or SelectDefault 1781 typ *rtype // channel type 1782 ch unsafe.Pointer // channel 1783 val unsafe.Pointer // ptr to data (SendDir) or ptr to receive buffer (RecvDir) 1784} 1785 1786// rselect runs a select. It returns the index of the chosen case. 1787// If the case was a receive, val is filled in with the received value. 1788// The conventional OK bool indicates whether the receive corresponds 1789// to a sent value. 1790//go:noescape 1791func rselect([]runtimeSelect) (chosen int, recvOK bool) 1792 1793// A SelectDir describes the communication direction of a select case. 1794type SelectDir int 1795 1796// NOTE: These values must match ../runtime/select.go:/selectDir. 1797 1798const ( 1799 _ SelectDir = iota 1800 SelectSend // case Chan <- Send 1801 SelectRecv // case <-Chan: 1802 SelectDefault // default 1803) 1804 1805// A SelectCase describes a single case in a select operation. 1806// The kind of case depends on Dir, the communication direction. 1807// 1808// If Dir is SelectDefault, the case represents a default case. 1809// Chan and Send must be zero Values. 1810// 1811// If Dir is SelectSend, the case represents a send operation. 1812// Normally Chan's underlying value must be a channel, and Send's underlying value must be 1813// assignable to the channel's element type. As a special case, if Chan is a zero Value, 1814// then the case is ignored, and the field Send will also be ignored and may be either zero 1815// or non-zero. 1816// 1817// If Dir is SelectRecv, the case represents a receive operation. 1818// Normally Chan's underlying value must be a channel and Send must be a zero Value. 1819// If Chan is a zero Value, then the case is ignored, but Send must still be a zero Value. 1820// When a receive operation is selected, the received Value is returned by Select. 1821// 1822type SelectCase struct { 1823 Dir SelectDir // direction of case 1824 Chan Value // channel to use (for send or receive) 1825 Send Value // value to send (for send) 1826} 1827 1828// Select executes a select operation described by the list of cases. 1829// Like the Go select statement, it blocks until at least one of the cases 1830// can proceed, makes a uniform pseudo-random choice, 1831// and then executes that case. It returns the index of the chosen case 1832// and, if that case was a receive operation, the value received and a 1833// boolean indicating whether the value corresponds to a send on the channel 1834// (as opposed to a zero value received because the channel is closed). 1835func Select(cases []SelectCase) (chosen int, recv Value, recvOK bool) { 1836 // NOTE: Do not trust that caller is not modifying cases data underfoot. 1837 // The range is safe because the caller cannot modify our copy of the len 1838 // and each iteration makes its own copy of the value c. 1839 runcases := make([]runtimeSelect, len(cases)) 1840 haveDefault := false 1841 for i, c := range cases { 1842 rc := &runcases[i] 1843 rc.dir = c.Dir 1844 switch c.Dir { 1845 default: 1846 panic("reflect.Select: invalid Dir") 1847 1848 case SelectDefault: // default 1849 if haveDefault { 1850 panic("reflect.Select: multiple default cases") 1851 } 1852 haveDefault = true 1853 if c.Chan.IsValid() { 1854 panic("reflect.Select: default case has Chan value") 1855 } 1856 if c.Send.IsValid() { 1857 panic("reflect.Select: default case has Send value") 1858 } 1859 1860 case SelectSend: 1861 ch := c.Chan 1862 if !ch.IsValid() { 1863 break 1864 } 1865 ch.mustBe(Chan) 1866 ch.mustBeExported() 1867 tt := (*chanType)(unsafe.Pointer(ch.typ)) 1868 if ChanDir(tt.dir)&SendDir == 0 { 1869 panic("reflect.Select: SendDir case using recv-only channel") 1870 } 1871 rc.ch = ch.pointer() 1872 rc.typ = &tt.rtype 1873 v := c.Send 1874 if !v.IsValid() { 1875 panic("reflect.Select: SendDir case missing Send value") 1876 } 1877 v.mustBeExported() 1878 v = v.assignTo("reflect.Select", tt.elem, nil) 1879 if v.flag&flagIndir != 0 { 1880 rc.val = v.ptr 1881 } else { 1882 rc.val = unsafe.Pointer(&v.ptr) 1883 } 1884 1885 case SelectRecv: 1886 if c.Send.IsValid() { 1887 panic("reflect.Select: RecvDir case has Send value") 1888 } 1889 ch := c.Chan 1890 if !ch.IsValid() { 1891 break 1892 } 1893 ch.mustBe(Chan) 1894 ch.mustBeExported() 1895 tt := (*chanType)(unsafe.Pointer(ch.typ)) 1896 if ChanDir(tt.dir)&RecvDir == 0 { 1897 panic("reflect.Select: RecvDir case using send-only channel") 1898 } 1899 rc.ch = ch.pointer() 1900 rc.typ = &tt.rtype 1901 rc.val = unsafe_New(tt.elem) 1902 } 1903 } 1904 1905 chosen, recvOK = rselect(runcases) 1906 if runcases[chosen].dir == SelectRecv { 1907 tt := (*chanType)(unsafe.Pointer(runcases[chosen].typ)) 1908 t := tt.elem 1909 p := runcases[chosen].val 1910 fl := flag(t.Kind()) 1911 if ifaceIndir(t) { 1912 recv = Value{t, p, fl | flagIndir} 1913 } else { 1914 recv = Value{t, *(*unsafe.Pointer)(p), fl} 1915 } 1916 } 1917 return chosen, recv, recvOK 1918} 1919 1920/* 1921 * constructors 1922 */ 1923 1924// implemented in package runtime 1925func unsafe_New(*rtype) unsafe.Pointer 1926func unsafe_NewArray(*rtype, int) unsafe.Pointer 1927 1928// MakeSlice creates a new zero-initialized slice value 1929// for the specified slice type, length, and capacity. 1930func MakeSlice(typ Type, len, cap int) Value { 1931 if typ.Kind() != Slice { 1932 panic("reflect.MakeSlice of non-slice type") 1933 } 1934 if len < 0 { 1935 panic("reflect.MakeSlice: negative len") 1936 } 1937 if cap < 0 { 1938 panic("reflect.MakeSlice: negative cap") 1939 } 1940 if len > cap { 1941 panic("reflect.MakeSlice: len > cap") 1942 } 1943 1944 s := sliceHeader{unsafe_NewArray(typ.Elem().(*rtype), cap), len, cap} 1945 return Value{typ.common(), unsafe.Pointer(&s), flagIndir | flag(Slice)} 1946} 1947 1948// MakeChan creates a new channel with the specified type and buffer size. 1949func MakeChan(typ Type, buffer int) Value { 1950 if typ.Kind() != Chan { 1951 panic("reflect.MakeChan of non-chan type") 1952 } 1953 if buffer < 0 { 1954 panic("reflect.MakeChan: negative buffer size") 1955 } 1956 if typ.ChanDir() != BothDir { 1957 panic("reflect.MakeChan: unidirectional channel type") 1958 } 1959 ch := makechan(typ.(*rtype), buffer) 1960 return Value{typ.common(), unsafe.Pointer(&ch), flag(Chan) | flagIndir} 1961} 1962 1963// MakeMap creates a new map with the specified type. 1964func MakeMap(typ Type) Value { 1965 return MakeMapWithSize(typ, 0) 1966} 1967 1968// MakeMapWithSize creates a new map with the specified type 1969// and initial space for approximately n elements. 1970func MakeMapWithSize(typ Type, n int) Value { 1971 if typ.Kind() != Map { 1972 panic("reflect.MakeMapWithSize of non-map type") 1973 } 1974 m := makemap(typ.(*rtype), n) 1975 return Value{typ.common(), unsafe.Pointer(&m), flag(Map) | flagIndir} 1976} 1977 1978// Indirect returns the value that v points to. 1979// If v is a nil pointer, Indirect returns a zero Value. 1980// If v is not a pointer, Indirect returns v. 1981func Indirect(v Value) Value { 1982 if v.Kind() != Ptr { 1983 return v 1984 } 1985 return v.Elem() 1986} 1987 1988// ValueOf returns a new Value initialized to the concrete value 1989// stored in the interface i. ValueOf(nil) returns the zero Value. 1990func ValueOf(i interface{}) Value { 1991 if i == nil { 1992 return Value{} 1993 } 1994 1995 // TODO: Maybe allow contents of a Value to live on the stack. 1996 // For now we make the contents always escape to the heap. It 1997 // makes life easier in a few places (see chanrecv/mapassign 1998 // comment below). 1999 escapes(i) 2000 2001 return unpackEface(i) 2002} 2003 2004// Zero returns a Value representing the zero value for the specified type. 2005// The result is different from the zero value of the Value struct, 2006// which represents no value at all. 2007// For example, Zero(TypeOf(42)) returns a Value with Kind Int and value 0. 2008// The returned value is neither addressable nor settable. 2009func Zero(typ Type) Value { 2010 if typ == nil { 2011 panic("reflect: Zero(nil)") 2012 } 2013 t := typ.common() 2014 fl := flag(t.Kind()) 2015 if ifaceIndir(t) { 2016 return Value{t, unsafe_New(typ.(*rtype)), fl | flagIndir} 2017 } 2018 return Value{t, nil, fl} 2019} 2020 2021// New returns a Value representing a pointer to a new zero value 2022// for the specified type. That is, the returned Value's Type is PtrTo(typ). 2023func New(typ Type) Value { 2024 if typ == nil { 2025 panic("reflect: New(nil)") 2026 } 2027 ptr := unsafe_New(typ.(*rtype)) 2028 fl := flag(Ptr) 2029 return Value{typ.common().ptrTo(), ptr, fl} 2030} 2031 2032// NewAt returns a Value representing a pointer to a value of the 2033// specified type, using p as that pointer. 2034func NewAt(typ Type, p unsafe.Pointer) Value { 2035 fl := flag(Ptr) 2036 return Value{typ.common().ptrTo(), p, fl} 2037} 2038 2039// assignTo returns a value v that can be assigned directly to typ. 2040// It panics if v is not assignable to typ. 2041// For a conversion to an interface type, target is a suggested scratch space to use. 2042func (v Value) assignTo(context string, dst *rtype, target unsafe.Pointer) Value { 2043 if v.flag&flagMethod != 0 { 2044 v = makeMethodValue(context, v) 2045 } 2046 2047 switch { 2048 case directlyAssignable(dst, v.typ): 2049 // Overwrite type so that they match. 2050 // Same memory layout, so no harm done. 2051 fl := v.flag&(flagAddr|flagIndir) | v.flag.ro() 2052 fl |= flag(dst.Kind()) 2053 return Value{dst, v.ptr, fl} 2054 2055 case implements(dst, v.typ): 2056 if target == nil { 2057 target = unsafe_New(dst) 2058 } 2059 if v.Kind() == Interface && v.IsNil() { 2060 // A nil ReadWriter passed to nil Reader is OK, 2061 // but using ifaceE2I below will panic. 2062 // Avoid the panic by returning a nil dst (e.g., Reader) explicitly. 2063 return Value{dst, nil, flag(Interface)} 2064 } 2065 x := valueInterface(v, false) 2066 if dst.NumMethod() == 0 { 2067 *(*interface{})(target) = x 2068 } else { 2069 ifaceE2I(dst, x, target) 2070 } 2071 return Value{dst, target, flagIndir | flag(Interface)} 2072 } 2073 2074 // Failed. 2075 panic(context + ": value of type " + v.typ.String() + " is not assignable to type " + dst.String()) 2076} 2077 2078// Convert returns the value v converted to type t. 2079// If the usual Go conversion rules do not allow conversion 2080// of the value v to type t, Convert panics. 2081func (v Value) Convert(t Type) Value { 2082 if v.flag&flagMethod != 0 { 2083 v = makeMethodValue("Convert", v) 2084 } 2085 op := convertOp(t.common(), v.typ) 2086 if op == nil { 2087 panic("reflect.Value.Convert: value of type " + v.typ.String() + " cannot be converted to type " + t.String()) 2088 } 2089 return op(v, t) 2090} 2091 2092// convertOp returns the function to convert a value of type src 2093// to a value of type dst. If the conversion is illegal, convertOp returns nil. 2094func convertOp(dst, src *rtype) func(Value, Type) Value { 2095 switch src.Kind() { 2096 case Int, Int8, Int16, Int32, Int64: 2097 switch dst.Kind() { 2098 case Int, Int8, Int16, Int32, Int64, Uint, Uint8, Uint16, Uint32, Uint64, Uintptr: 2099 return cvtInt 2100 case Float32, Float64: 2101 return cvtIntFloat 2102 case String: 2103 return cvtIntString 2104 } 2105 2106 case Uint, Uint8, Uint16, Uint32, Uint64, Uintptr: 2107 switch dst.Kind() { 2108 case Int, Int8, Int16, Int32, Int64, Uint, Uint8, Uint16, Uint32, Uint64, Uintptr: 2109 return cvtUint 2110 case Float32, Float64: 2111 return cvtUintFloat 2112 case String: 2113 return cvtUintString 2114 } 2115 2116 case Float32, Float64: 2117 switch dst.Kind() { 2118 case Int, Int8, Int16, Int32, Int64: 2119 return cvtFloatInt 2120 case Uint, Uint8, Uint16, Uint32, Uint64, Uintptr: 2121 return cvtFloatUint 2122 case Float32, Float64: 2123 return cvtFloat 2124 } 2125 2126 case Complex64, Complex128: 2127 switch dst.Kind() { 2128 case Complex64, Complex128: 2129 return cvtComplex 2130 } 2131 2132 case String: 2133 if dst.Kind() == Slice && dst.Elem().PkgPath() == "" { 2134 switch dst.Elem().Kind() { 2135 case Uint8: 2136 return cvtStringBytes 2137 case Int32: 2138 return cvtStringRunes 2139 } 2140 } 2141 2142 case Slice: 2143 if dst.Kind() == String && src.Elem().PkgPath() == "" { 2144 switch src.Elem().Kind() { 2145 case Uint8: 2146 return cvtBytesString 2147 case Int32: 2148 return cvtRunesString 2149 } 2150 } 2151 } 2152 2153 // dst and src have same underlying type. 2154 if haveIdenticalUnderlyingType(dst, src, false) { 2155 return cvtDirect 2156 } 2157 2158 // dst and src are unnamed pointer types with same underlying base type. 2159 if dst.Kind() == Ptr && dst.Name() == "" && 2160 src.Kind() == Ptr && src.Name() == "" && 2161 haveIdenticalUnderlyingType(dst.Elem().common(), src.Elem().common(), false) { 2162 return cvtDirect 2163 } 2164 2165 if implements(dst, src) { 2166 if src.Kind() == Interface { 2167 return cvtI2I 2168 } 2169 return cvtT2I 2170 } 2171 2172 return nil 2173} 2174 2175// makeInt returns a Value of type t equal to bits (possibly truncated), 2176// where t is a signed or unsigned int type. 2177func makeInt(f flag, bits uint64, t Type) Value { 2178 typ := t.common() 2179 ptr := unsafe_New(typ) 2180 switch typ.size { 2181 case 1: 2182 *(*uint8)(ptr) = uint8(bits) 2183 case 2: 2184 *(*uint16)(ptr) = uint16(bits) 2185 case 4: 2186 *(*uint32)(ptr) = uint32(bits) 2187 case 8: 2188 *(*uint64)(ptr) = bits 2189 } 2190 return Value{typ, ptr, f | flagIndir | flag(typ.Kind())} 2191} 2192 2193// makeFloat returns a Value of type t equal to v (possibly truncated to float32), 2194// where t is a float32 or float64 type. 2195func makeFloat(f flag, v float64, t Type) Value { 2196 typ := t.common() 2197 ptr := unsafe_New(typ) 2198 switch typ.size { 2199 case 4: 2200 *(*float32)(ptr) = float32(v) 2201 case 8: 2202 *(*float64)(ptr) = v 2203 } 2204 return Value{typ, ptr, f | flagIndir | flag(typ.Kind())} 2205} 2206 2207// makeComplex returns a Value of type t equal to v (possibly truncated to complex64), 2208// where t is a complex64 or complex128 type. 2209func makeComplex(f flag, v complex128, t Type) Value { 2210 typ := t.common() 2211 ptr := unsafe_New(typ) 2212 switch typ.size { 2213 case 8: 2214 *(*complex64)(ptr) = complex64(v) 2215 case 16: 2216 *(*complex128)(ptr) = v 2217 } 2218 return Value{typ, ptr, f | flagIndir | flag(typ.Kind())} 2219} 2220 2221func makeString(f flag, v string, t Type) Value { 2222 ret := New(t).Elem() 2223 ret.SetString(v) 2224 ret.flag = ret.flag&^flagAddr | f 2225 return ret 2226} 2227 2228func makeBytes(f flag, v []byte, t Type) Value { 2229 ret := New(t).Elem() 2230 ret.SetBytes(v) 2231 ret.flag = ret.flag&^flagAddr | f 2232 return ret 2233} 2234 2235func makeRunes(f flag, v []rune, t Type) Value { 2236 ret := New(t).Elem() 2237 ret.setRunes(v) 2238 ret.flag = ret.flag&^flagAddr | f 2239 return ret 2240} 2241 2242// These conversion functions are returned by convertOp 2243// for classes of conversions. For example, the first function, cvtInt, 2244// takes any value v of signed int type and returns the value converted 2245// to type t, where t is any signed or unsigned int type. 2246 2247// convertOp: intXX -> [u]intXX 2248func cvtInt(v Value, t Type) Value { 2249 return makeInt(v.flag.ro(), uint64(v.Int()), t) 2250} 2251 2252// convertOp: uintXX -> [u]intXX 2253func cvtUint(v Value, t Type) Value { 2254 return makeInt(v.flag.ro(), v.Uint(), t) 2255} 2256 2257// convertOp: floatXX -> intXX 2258func cvtFloatInt(v Value, t Type) Value { 2259 return makeInt(v.flag.ro(), uint64(int64(v.Float())), t) 2260} 2261 2262// convertOp: floatXX -> uintXX 2263func cvtFloatUint(v Value, t Type) Value { 2264 return makeInt(v.flag.ro(), uint64(v.Float()), t) 2265} 2266 2267// convertOp: intXX -> floatXX 2268func cvtIntFloat(v Value, t Type) Value { 2269 return makeFloat(v.flag.ro(), float64(v.Int()), t) 2270} 2271 2272// convertOp: uintXX -> floatXX 2273func cvtUintFloat(v Value, t Type) Value { 2274 return makeFloat(v.flag.ro(), float64(v.Uint()), t) 2275} 2276 2277// convertOp: floatXX -> floatXX 2278func cvtFloat(v Value, t Type) Value { 2279 return makeFloat(v.flag.ro(), v.Float(), t) 2280} 2281 2282// convertOp: complexXX -> complexXX 2283func cvtComplex(v Value, t Type) Value { 2284 return makeComplex(v.flag.ro(), v.Complex(), t) 2285} 2286 2287// convertOp: intXX -> string 2288func cvtIntString(v Value, t Type) Value { 2289 return makeString(v.flag.ro(), string(v.Int()), t) 2290} 2291 2292// convertOp: uintXX -> string 2293func cvtUintString(v Value, t Type) Value { 2294 return makeString(v.flag.ro(), string(v.Uint()), t) 2295} 2296 2297// convertOp: []byte -> string 2298func cvtBytesString(v Value, t Type) Value { 2299 return makeString(v.flag.ro(), string(v.Bytes()), t) 2300} 2301 2302// convertOp: string -> []byte 2303func cvtStringBytes(v Value, t Type) Value { 2304 return makeBytes(v.flag.ro(), []byte(v.String()), t) 2305} 2306 2307// convertOp: []rune -> string 2308func cvtRunesString(v Value, t Type) Value { 2309 return makeString(v.flag.ro(), string(v.runes()), t) 2310} 2311 2312// convertOp: string -> []rune 2313func cvtStringRunes(v Value, t Type) Value { 2314 return makeRunes(v.flag.ro(), []rune(v.String()), t) 2315} 2316 2317// convertOp: direct copy 2318func cvtDirect(v Value, typ Type) Value { 2319 f := v.flag 2320 t := typ.common() 2321 ptr := v.ptr 2322 if f&flagAddr != 0 { 2323 // indirect, mutable word - make a copy 2324 c := unsafe_New(t) 2325 typedmemmove(t, c, ptr) 2326 ptr = c 2327 f &^= flagAddr 2328 } 2329 return Value{t, ptr, v.flag.ro() | f} // v.flag.ro()|f == f? 2330} 2331 2332// convertOp: concrete -> interface 2333func cvtT2I(v Value, typ Type) Value { 2334 target := unsafe_New(typ.common()) 2335 x := valueInterface(v, false) 2336 if typ.NumMethod() == 0 { 2337 *(*interface{})(target) = x 2338 } else { 2339 ifaceE2I(typ.(*rtype), x, target) 2340 } 2341 return Value{typ.common(), target, v.flag.ro() | flagIndir | flag(Interface)} 2342} 2343 2344// convertOp: interface -> interface 2345func cvtI2I(v Value, typ Type) Value { 2346 if v.IsNil() { 2347 ret := Zero(typ) 2348 ret.flag |= v.flag.ro() 2349 return ret 2350 } 2351 return cvtT2I(v.Elem(), typ) 2352} 2353 2354// implemented in ../runtime 2355func chancap(ch unsafe.Pointer) int 2356func chanclose(ch unsafe.Pointer) 2357func chanlen(ch unsafe.Pointer) int 2358 2359// Note: some of the noescape annotations below are technically a lie, 2360// but safe in the context of this package. Functions like chansend 2361// and mapassign don't escape the referent, but may escape anything 2362// the referent points to (they do shallow copies of the referent). 2363// It is safe in this package because the referent may only point 2364// to something a Value may point to, and that is always in the heap 2365// (due to the escapes() call in ValueOf). 2366 2367//go:noescape 2368func chanrecv(ch unsafe.Pointer, nb bool, val unsafe.Pointer) (selected, received bool) 2369 2370//go:noescape 2371func chansend(ch unsafe.Pointer, val unsafe.Pointer, nb bool) bool 2372 2373func makechan(typ *rtype, size int) (ch unsafe.Pointer) 2374func makemap(t *rtype, cap int) (m unsafe.Pointer) 2375 2376//go:noescape 2377func mapaccess(t *rtype, m unsafe.Pointer, key unsafe.Pointer) (val unsafe.Pointer) 2378 2379//go:noescape 2380func mapassign(t *rtype, m unsafe.Pointer, key, val unsafe.Pointer) 2381 2382//go:noescape 2383func mapdelete(t *rtype, m unsafe.Pointer, key unsafe.Pointer) 2384 2385// m escapes into the return value, but the caller of mapiterinit 2386// doesn't let the return value escape. 2387//go:noescape 2388func mapiterinit(t *rtype, m unsafe.Pointer) unsafe.Pointer 2389 2390//go:noescape 2391func mapiterkey(it unsafe.Pointer) (key unsafe.Pointer) 2392 2393//go:noescape 2394func mapiternext(it unsafe.Pointer) 2395 2396//go:noescape 2397func maplen(m unsafe.Pointer) int 2398func call(typ *rtype, fnaddr unsafe.Pointer, isInterface bool, isMethod bool, params *unsafe.Pointer, results *unsafe.Pointer) 2399 2400func ifaceE2I(t *rtype, src interface{}, dst unsafe.Pointer) 2401 2402// typedmemmove copies a value of type t to dst from src. 2403//go:noescape 2404func typedmemmove(t *rtype, dst, src unsafe.Pointer) 2405 2406// typedslicecopy copies a slice of elemType values from src to dst, 2407// returning the number of elements copied. 2408//go:noescape 2409func typedslicecopy(elemType *rtype, dst, src sliceHeader) int 2410 2411//go:noescape 2412//extern memmove 2413func memmove(adst, asrc unsafe.Pointer, n uintptr) 2414 2415// Dummy annotation marking that the value x escapes, 2416// for use in cases where the reflect code is so clever that 2417// the compiler cannot follow. 2418func escapes(x interface{}) { 2419 if dummy.b { 2420 dummy.x = x 2421 } 2422} 2423 2424var dummy struct { 2425 b bool 2426 x interface{} 2427} 2428