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reflect: make Index and Slice accept strings

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Fixes #3284.

R=golang-dev, r, rsc
CC=golang-dev
https://golang.org/cl/6643043
This commit is contained in:
Evan Shaw 2012-10-21 17:02:10 -04:00 committed by Russ Cox
parent d7a3407e3d
commit 772decbc80
2 changed files with 49 additions and 3 deletions
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24
src/pkg/reflect/all_test.go
View File

@ -2036,6 +2036,24 @@ func TestSmallNegativeInt(t *testing.T) {
}
}
func TestIndex(t *testing.T) {
xs := []byte{1, 2, 3, 4, 5, 6, 7, 8}
v := ValueOf(xs).Index(3).Interface().(byte)
if v != xs[3] {
t.Errorf("xs.Index(3) = %v; expected %v", v, xs[3])
}
xa := [8]byte{10, 20, 30, 40, 50, 60, 70, 80}
v = ValueOf(xa).Index(2).Interface().(byte)
if v != xa[2] {
t.Errorf("xa.Index(2) = %v; expected %v", v, xa[2])
}
s := "0123456789"
v = ValueOf(s).Index(3).Interface().(byte)
if v != s[3] {
t.Errorf("s.Index(3) = %v; expected %v", v, s[3])
}
}
func TestSlice(t *testing.T) {
xs := []int{1, 2, 3, 4, 5, 6, 7, 8}
v := ValueOf(xs).Slice(3, 5).Interface().([]int)
@ -2048,7 +2066,6 @@ func TestSlice(t *testing.T) {
if !DeepEqual(v[0:5], xs[3:]) {
t.Errorf("xs.Slice(3, 5)[0:5] = %v", v[0:5])
}
xa := [8]int{10, 20, 30, 40, 50, 60, 70, 80}
v = ValueOf(&xa).Elem().Slice(2, 5).Interface().([]int)
if len(v) != 3 {
@ -2060,6 +2077,11 @@ func TestSlice(t *testing.T) {
if !DeepEqual(v[0:6], xa[2:]) {
t.Errorf("xs.Slice(2, 5)[0:6] = %v", v[0:6])
}
s := "0123456789"
vs := ValueOf(s).Slice(3, 5).Interface().(string)
if vs != s[3:5] {
t.Errorf("s.Slice(3, 5) = %q; expected %q", vs, s[3:5])
}
}
func TestVariadic(t *testing.T) {

28
src/pkg/reflect/value.go
View File

@ -810,8 +810,10 @@ func (v Value) Float() float64 {
panic(&ValueError{"reflect.Value.Float", k})
}
var uint8Type = TypeOf(uint8(0)).(*commonType)
// Index returns v's i'th element.
// It panics if v's Kind is not Array or Slice or i is out of range.
// It panics if v's Kind is not Array, Slice, or String or i is out of range.
func (v Value) Index(i int) Value {
k := v.kind()
switch k {
@ -852,6 +854,15 @@ func (v Value) Index(i int) Value {
fl |= flag(typ.Kind()) << flagKindShift
val := unsafe.Pointer(s.Data + uintptr(i)*typ.size)
return Value{typ, val, fl}
case String:
fl := v.flag&flagRO | flag(Uint8<<flagKindShift)
s := (*StringHeader)(v.val)
if i < 0 || i >= s.Len {
panic("reflect: string index out of range")
}
val := *(*byte)(unsafe.Pointer(s.Data + uintptr(i)))
return Value{uint8Type, unsafe.Pointer(uintptr(val)), fl}
}
panic(&ValueError{"reflect.Value.Index", k})
}
@ -1437,7 +1448,7 @@ func (v Value) SetString(x string) {
}
// Slice returns a slice of v.
// It panics if v's Kind is not Array or Slice.
// It panics if v's Kind is not Array, Slice, or String.
func (v Value) Slice(beg, end int) Value {
var (
cap int
@ -1447,6 +1458,7 @@ func (v Value) Slice(beg, end int) Value {
switch k := v.kind(); k {
default:
panic(&ValueError{"reflect.Value.Slice", k})
case Array:
if v.flag&flagAddr == 0 {
panic("reflect.Value.Slice: slice of unaddressable array")
@ -1455,13 +1467,25 @@ func (v Value) Slice(beg, end int) Value {
cap = int(tt.len)
typ = (*sliceType)(unsafe.Pointer(toCommonType(tt.slice)))
base = v.val
case Slice:
typ = (*sliceType)(unsafe.Pointer(v.typ))
s := (*SliceHeader)(v.val)
base = unsafe.Pointer(s.Data)
cap = s.Cap
case String:
s := (*StringHeader)(v.val)
if beg < 0 || end < beg || end > s.Len {
panic("reflect.Value.Slice: string slice index out of bounds")
}
var x string
val := (*StringHeader)(unsafe.Pointer(&x))
val.Data = s.Data + uintptr(beg)
val.Len = end - beg
return Value{v.typ, unsafe.Pointer(&x), v.flag}
}
if beg < 0 || end < beg || end > cap {
panic("reflect.Value.Slice: slice index out of bounds")
}