Add: slice <--> string

strings/nil.go

+// Copyright 2016 ~ 2018 AlexStocks(https://github.com/AlexStocks).
+// All rights reserved.  Use of this source code is
+// governed by Apache License 2.0.
+
+package gxstrings
+
+import (
+	"reflect"
+)
+
+func IsNil(i interface{}) bool {
+	if i == nil {
+		return true
+	}
+
+	if reflect.ValueOf(i).IsNil() {
+		return true
+	}
+
+	return false
+}

strings/slice.go

+// Copyright 2016 ~ 2018 AlexStocks(https://github.com/AlexStocks).
+// All rights reserved.  Use of this source code is
+// governed by Apache License 2.0.
+
+// http://blog.csdn.net/siddontang/article/details/23541587
+// reflect.StringHeader和reflect.SliceHeader的结构体只相差末尾一个字段(cap)
+// vitess代码，一种很hack的做法，string和slice的转换只需要拷贝底层的指针，而不是内存拷贝。
+package gxstrings
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+func String(b []byte) (s string) {
+	pbytes := (*reflect.SliceHeader)(unsafe.Pointer(&b))
+	pstring := (*reflect.StringHeader)(unsafe.Pointer(&s))
+	pstring.Data = pbytes.Data
+	pstring.Len = pbytes.Len
+	return
+}
+
+func Slice(s string) (b []byte) {
+	pbytes := (*reflect.SliceHeader)(unsafe.Pointer(&b))
+	pstring := (*reflect.StringHeader)(unsafe.Pointer(&s))
+	pbytes.Data = pstring.Data
+	pbytes.Len = pstring.Len
+	pbytes.Cap = pstring.Len
+	return
+}
+
+// returns &s[0], which is not allowed in go
+func StringPointer(s string) unsafe.Pointer {
+	p := (*reflect.StringHeader)(unsafe.Pointer(&s))
+	return unsafe.Pointer(p.Data)
+}
+
+// returns &b[0], which is not allowed in go
+func BytePointer(b []byte) unsafe.Pointer {
+	p := (*reflect.SliceHeader)(unsafe.Pointer(&b))
+	return unsafe.Pointer(p.Data)
+}
+

strings/slice_test.go

+package gxstrings
+
+import (
+	"testing"
+)
+
+// go test  -v slice_test.go  slice.go
+
+// slice转string之后，如果slice的值有变化，string也会跟着改变
+func TestString(t *testing.T) {
+	b := []byte("hello world")
+	a := String(b)
+	b[0] = 'a'
+	println(a) //output  aello world
+}
+
+func TestSlice(t *testing.T) {
+	// 编译器会把 "hello, world" 这个字符串常量的字节数组分配在没有写权限的 memory segment
+	a := "hello world"
+	b := Slice(a)
+
+	// !!! 上面这个崩溃在defer里面是recover不回来的，真的就崩溃了，原因可能就跟c的非法内存访问一样，os不跟你玩了
+	// b[0] = 'a' //这里就等着崩溃吧
+
+	//但是可以这样，因为go又重新给b分配了内存
+	b = append(b, "hello world"...)
+	println(String(b)) // output: hello worldhello world
+}
+
+func TestSlice2(t *testing.T) {
+	// 你可以动态生成一个字符串，使其分配在可写的区域，比如 gc heap，那么就不会崩溃了。
+	a := string([]byte("hello world"))
+	b := Slice(a)
+	b = append(b, "hello world"...)
+	println(String(b)) // output: hello worldhello world
+}
+