diff --git a/src/strings/clone.go b/src/strings/clone.go new file mode 100644 index 0000000000..6097c6cc88 --- /dev/null +++ b/src/strings/clone.go @@ -0,0 +1,23 @@ +// Copyright 2021 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 strings + +import ( + "unsafe" +) + +// Clone returns a fresh copy of s. +// It guarantees to make a copy of s into a new allocation, +// which can be important when retaining only a small substring +// of a much larger string. Using Clone can help such programs +// use less memory. Of course, since using Clone makes a copy, +// overuse of Clone can make programs use more memory. +// Clone should typically be used only rarely, and only when +// profiling indicates that it is needed. +func Clone(s string) string { + b := make([]byte, len(s)) + copy(b, s) + return *(*string)(unsafe.Pointer(&b)) +} diff --git a/src/strings/clone_test.go b/src/strings/clone_test.go new file mode 100644 index 0000000000..5396771047 --- /dev/null +++ b/src/strings/clone_test.go @@ -0,0 +1,40 @@ +// Copyright 2021 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.ß + +package strings_test + +import ( + "reflect" + "strings" + "testing" + "unsafe" +) + +func TestClone(t *testing.T) { + var cloneTests = []string{ + "", + "short", + strings.Repeat("a", 42), + } + for _, input := range cloneTests { + clone := strings.Clone(input) + if clone != input { + t.Errorf("Clone(%q) = %q; want %q", input, clone, input) + } + + inputHeader := (*reflect.StringHeader)(unsafe.Pointer(&input)) + cloneHeader := (*reflect.StringHeader)(unsafe.Pointer(&clone)) + if inputHeader.Data == cloneHeader.Data { + t.Errorf("Clone(%q) return value should not reference inputs backing memory.", input) + } + } +} + +func BenchmarkClone(b *testing.B) { + var str = strings.Repeat("a", 42) + b.ReportAllocs() + for i := 0; i < b.N; i++ { + stringSink = strings.Clone(str) + } +}