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reflect: add Value.Slice3 and Value.SetCap methods, to match x[i:j:k]
Design doc at golang.org/s/go12slice. R=golang-dev, r, nightlyone CC=golang-dev https://golang.org/cl/10761045
This commit is contained in:
Russ Cox
parent
b4e92cee97
commit
4d8aefde47
@ -2368,6 +2368,74 @@ func TestSlice(t *testing.T) {
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}
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}
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func TestSlice3(t *testing.T) {
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xs := []int{1, 2, 3, 4, 5, 6, 7, 8}
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v := ValueOf(xs).Slice3(3, 5, 7).Interface().([]int)
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if len(v) != 2 {
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t.Errorf("len(xs.Slice3(3, 5, 7)) = %d", len(v))
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}
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if cap(v) != 4 {
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t.Errorf("cap(xs.Slice3(3, 5, 7)) = %d", cap(v))
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}
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if !DeepEqual(v[0:4], xs[3:7:7]) {
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t.Errorf("xs.Slice3(3, 5, 7)[0:4] = %v", v[0:4])
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}
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rv := ValueOf(&xs).Elem()
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shouldPanic(func() { rv.Slice3(1, 2, 1) })
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shouldPanic(func() { rv.Slice3(1, 1, 11) })
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shouldPanic(func() { rv.Slice3(2, 2, 1) })
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xa := [8]int{10, 20, 30, 40, 50, 60, 70, 80}
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v = ValueOf(&xa).Elem().Slice3(2, 5, 6).Interface().([]int)
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if len(v) != 3 {
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t.Errorf("len(xa.Slice(2, 5, 6)) = %d", len(v))
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}
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if cap(v) != 4 {
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t.Errorf("cap(xa.Slice(2, 5, 6)) = %d", cap(v))
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}
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if !DeepEqual(v[0:4], xa[2:6:6]) {
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t.Errorf("xs.Slice(2, 5, 6)[0:4] = %v", v[0:4])
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}
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rv = ValueOf(&xa).Elem()
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shouldPanic(func() { rv.Slice3(1, 2, 1) })
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shouldPanic(func() { rv.Slice3(1, 1, 11) })
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shouldPanic(func() { rv.Slice3(2, 2, 1) })
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s := "hello world"
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rv = ValueOf(&s).Elem()
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shouldPanic(func() { rv.Slice3(1, 2, 3) })
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}
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func TestSetLenCap(t *testing.T) {
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xs := []int{1, 2, 3, 4, 5, 6, 7, 8}
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xa := [8]int{10, 20, 30, 40, 50, 60, 70, 80}
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vs := ValueOf(&xs).Elem()
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shouldPanic(func() { vs.SetLen(10) })
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shouldPanic(func() { vs.SetCap(10) })
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shouldPanic(func() { vs.SetLen(-1) })
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shouldPanic(func() { vs.SetCap(-1) })
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shouldPanic(func() { vs.SetCap(6) }) // smaller than len
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vs.SetLen(5)
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if len(xs) != 5 || cap(xs) != 8 {
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t.Errorf("after SetLen(5), len, cap = %d, %d, want 5, 8", len(xs), cap(xs))
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}
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vs.SetCap(6)
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if len(xs) != 5 || cap(xs) != 6 {
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t.Errorf("after SetCap(6), len, cap = %d, %d, want 5, 6", len(xs), cap(xs))
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}
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vs.SetCap(5)
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if len(xs) != 5 || cap(xs) != 5 {
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t.Errorf("after SetCap(5), len, cap = %d, %d, want 5, 5", len(xs), cap(xs))
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}
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shouldPanic(func() { vs.SetCap(4) }) // smaller than len
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shouldPanic(func() { vs.SetLen(6) }) // bigger than cap
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va := ValueOf(&xa).Elem()
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shouldPanic(func() { va.SetLen(8) })
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shouldPanic(func() { va.SetCap(8) })
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}
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func TestVariadic(t *testing.T) {
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var b bytes.Buffer
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V := ValueOf
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@ -1475,6 +1475,19 @@ func (v Value) SetLen(n int) {
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s.Len = n
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}
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// SetCap sets v's capacity to n.
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// It panics if v's Kind is not Slice or if n is smaller than the length or
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// greater than the capacity of the slice.
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func (v Value) SetCap(n int) {
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v.mustBeAssignable()
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v.mustBe(Slice)
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s := (*SliceHeader)(v.val)
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if n < int(s.Len) || n > int(s.Cap) {
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panic("reflect: slice capacity out of range in SetCap")
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}
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s.Cap = n
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}
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// SetMapIndex sets the value associated with key in the map v to val.
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// It panics if v's Kind is not Map.
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// If val is the zero Value, SetMapIndex deletes the key from the map.
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@ -1531,17 +1544,18 @@ func (v Value) SetString(x string) {
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*(*string)(v.val) = x
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}
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// Slice returns a slice of v.
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// It panics if v's Kind is not Array, Slice or String, or if v is an unaddressable array.
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func (v Value) Slice(beg, end int) Value {
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// Slice returns v[i:j].
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// It panics if v's Kind is not Array, Slice or String, or if v is an unaddressable array,
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// or if the indexes are out of bounds.
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func (v Value) Slice(i, j int) Value {
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var (
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cap int
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typ *sliceType
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base unsafe.Pointer
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)
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switch k := v.kind(); k {
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switch kind := v.kind(); kind {
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default:
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panic(&ValueError{"reflect.Value.Slice", k})
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panic(&ValueError{"reflect.Value.Slice", kind})
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case Array:
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if v.flag&flagAddr == 0 {
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@ -1560,17 +1574,17 @@ func (v Value) Slice(beg, end int) Value {
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case String:
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s := (*StringHeader)(v.val)
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if beg < 0 || end < beg || end > s.Len {
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if i < 0 || j < i || j > s.Len {
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panic("reflect.Value.Slice: string slice index out of bounds")
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}
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var x string
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val := (*StringHeader)(unsafe.Pointer(&x))
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val.Data = s.Data + uintptr(beg)
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val.Len = end - beg
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val.Data = s.Data + uintptr(i)
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val.Len = j - i
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return Value{v.typ, unsafe.Pointer(&x), v.flag}
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}
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if beg < 0 || end < beg || end > cap {
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if i < 0 || j < i || j > cap {
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panic("reflect.Value.Slice: slice index out of bounds")
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}
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@ -1579,9 +1593,56 @@ func (v Value) Slice(beg, end int) Value {
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// Reinterpret as *SliceHeader to edit.
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s := (*SliceHeader)(unsafe.Pointer(&x))
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s.Data = uintptr(base) + uintptr(beg)*typ.elem.Size()
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s.Len = end - beg
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s.Cap = cap - beg
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s.Data = uintptr(base) + uintptr(i)*typ.elem.Size()
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s.Len = j - i
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s.Cap = cap - i
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fl := v.flag&flagRO | flagIndir | flag(Slice)<<flagKindShift
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return Value{typ.common(), unsafe.Pointer(&x), fl}
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}
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// Slice3 is the 3-index form of the slice operation: it returns v[i:j:k].
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// It panics if v's Kind is not Array or Slice, or if v is an unaddressable array,
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// or if the indexes are out of bounds.
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func (v Value) Slice3(i, j, k int) Value {
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var (
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cap int
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typ *sliceType
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base unsafe.Pointer
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)
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switch kind := v.kind(); kind {
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default:
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panic(&ValueError{"reflect.Value.Slice3", kind})
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case Array:
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if v.flag&flagAddr == 0 {
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panic("reflect.Value.Slice: slice of unaddressable array")
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}
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tt := (*arrayType)(unsafe.Pointer(v.typ))
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cap = int(tt.len)
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typ = (*sliceType)(unsafe.Pointer(tt.slice))
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base = v.val
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case Slice:
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typ = (*sliceType)(unsafe.Pointer(v.typ))
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s := (*SliceHeader)(v.val)
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base = unsafe.Pointer(s.Data)
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cap = s.Cap
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}
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if i < 0 || j < i || k < j || k > cap {
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panic("reflect.Value.Slice3: slice index out of bounds")
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}
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// Declare slice so that the garbage collector
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// can see the base pointer in it.
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var x []unsafe.Pointer
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// Reinterpret as *SliceHeader to edit.
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s := (*SliceHeader)(unsafe.Pointer(&x))
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s.Data = uintptr(base) + uintptr(i)*typ.elem.Size()
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s.Len = j - i
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s.Cap = k - i
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fl := v.flag&flagRO | flagIndir | flag(Slice)<<flagKindShift
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return Value{typ.common(), unsafe.Pointer(&x), fl}
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