// Copyright 2016 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. package reflectlite import ( "internal/unsafeheader" "unsafe" ) // Swapper returns a function that swaps the elements in the provided // slice. // // Swapper panics if the provided interface is not a slice. func Swapper(slice interface{}) func(i, j int) { v := ValueOf(slice) if v.Kind() != Slice { panic(&ValueError{Method: "Swapper", Kind: v.Kind()}) } // Fast path for slices of size 0 and 1. Nothing to swap. switch v.Len() { case 0: return func(i, j int) { panic("reflect: slice index out of range") } case 1: return func(i, j int) { if i != 0 || j != 0 { panic("reflect: slice index out of range") } } } typ := v.Type().Elem().(*rtype) size := typ.Size() hasPtr := typ.ptrdata != 0 // Some common & small cases, without using memmove: if hasPtr { if size == ptrSize { ps := *(*[]unsafe.Pointer)(v.ptr) return func(i, j int) { ps[i], ps[j] = ps[j], ps[i] } } if typ.Kind() == String { ss := *(*[]string)(v.ptr) return func(i, j int) { ss[i], ss[j] = ss[j], ss[i] } } } else { switch size { case 8: is := *(*[]int64)(v.ptr) return func(i, j int) { is[i], is[j] = is[j], is[i] } case 4: is := *(*[]int32)(v.ptr) return func(i, j int) { is[i], is[j] = is[j], is[i] } case 2: is := *(*[]int16)(v.ptr) return func(i, j int) { is[i], is[j] = is[j], is[i] } case 1: is := *(*[]int8)(v.ptr) return func(i, j int) { is[i], is[j] = is[j], is[i] } } } s := (*unsafeheader.Slice)(v.ptr) tmp := unsafe_New(typ) // swap scratch space return func(i, j int) { if uint(i) >= uint(s.Len) || uint(j) >= uint(s.Len) { panic("reflect: slice index out of range") } val1 := arrayAt(s.Data, i, size, "i < s.Len") val2 := arrayAt(s.Data, j, size, "j < s.Len") typedmemmove(typ, tmp, val1) typedmemmove(typ, val1, val2) typedmemmove(typ, val2, tmp) } }