完善go切片文章

docs/dev/language/golang/code/slice_test.go

@@ -0,0 +1,131 @@
+package code
+
+import (
+	"fmt"
+	"github.com/stretchr/testify/assert"
+	"reflect"
+	"testing"
+	"unsafe"
+)
+
+func TestSliceArray(t *testing.T) {
+	var arr = [...]int{1, 2, 3}
+	var slice = []int{1, 2, 3}
+	ModifyArray(arr)
+	ModifySlice(slice)
+	t.Logf("%v %v\n", arr, slice)
+	assert.NotEqual(t, arr[2], 1)
+	assert.Equal(t, slice[2], 1)
+}
+
+func ModifyArray(arr [3]int) {
+	fmt.Println(arr)
+	arr[2] = 1
+}
+
+func ModifySlice(slice []int) {
+	fmt.Println(slice)
+	slice[2] = 1
+}
+
+func TestSlice(t *testing.T) {
+	slice := []int{1, 2, 3}
+	arr := [...]int{1, 2, 3}
+	fmt.Printf("切片：底层数组指针：%d 切片：指针%v reflect.SliceHeader: %+v\n",
+		unsafe.SliceData(slice), unsafe.Pointer(&slice), (*reflect.SliceHeader)(unsafe.Pointer(&slice)))
+	SlicePointer(slice)
+	fmt.Printf("数组：底层数组指针：%d 数组指针：%d\n", unsafe.Pointer(&arr), unsafe.Pointer(&arr[0]))
+	ArrayPointer(arr)
+}
+
+func SlicePointer(slice []int) {
+	fmt.Printf("切片：底层数组指针：%d 切片：指针%v reflect.SliceHeader: %+v\n",
+		unsafe.SliceData(slice), unsafe.Pointer(&slice), (*reflect.SliceHeader)(unsafe.Pointer(&slice)))
+}
+
+func ArrayPointer(arr [3]int) {
+	fmt.Printf("数组：底层数组指针：%d 数组指针：%d\n", unsafe.Pointer(&arr), unsafe.Pointer(&arr[0]))
+}
+
+func TestModify(t *testing.T) {
+	arr := [...]int{1, 2, 3, 4, 5, 6, 7}
+	slice := arr[:]
+	slice[4] = 8
+	t.Logf("arr[4]=%v,slice[4]=%v\n", arr[4], slice[4])
+	assert.Equal(t, slice[4], arr[4])
+	slice = append(slice, 9)
+	slice[5] = 10
+	t.Logf("arr[4]=%v,slice[4]=%v\n", arr[4], slice[4])
+	assert.Equal(t, slice[4], arr[4])
+	t.Logf("arr[5]=%v,slice[5]=%v\n", arr[5], slice[5])
+	assert.NotEqual(t, slice[5], arr[5])
+}
+
+func TestModifyTwoSlice(t *testing.T) {
+	arr := [...]int{1, 2, 3, 4, 5, 6, 7, 8, 9}
+	slice1 := arr[1:5]
+	slice2 := arr[3:8]
+	slice1[2] = 8
+	t.Logf("%v %v %v\n", arr, slice1, slice2)
+	assert.Equal(t, slice1[2], slice2[0], arr[3])
+}
+
+func TestCap(t *testing.T) {
+	slice := []int{1, 2, 3, 4}
+	fmt.Printf("len:%d cap: %d\n", len(slice), cap(slice))
+	slice = append(slice, make([]int, 11)...)
+	fmt.Printf("len:%d cap: %d\n", len(slice), cap(slice)) // oldcap<256，直接使用新切片容量
+	slice = append(slice, make([]int, 260)...)
+	fmt.Printf("len:%d cap: %d\n", len(slice), cap(slice)) // oldcap<256，直接使用新切片容量
+	slice = append(slice, make([]int, 250)...)
+	fmt.Printf("len:%d cap: %d\n", len(slice), cap(slice)) // 1.25倍循环扩容
+}
+
+func TestString(t *testing.T) {
+	str := "hello"
+	fmt.Printf("%d %+v\n", &str, (*reflect.StringHeader)(unsafe.Pointer(&str)))
+	str = "world"
+	fmt.Printf("%d %+v\n", &str, (*reflect.StringHeader)(unsafe.Pointer(&str)))
+	str = str[:3]
+	fmt.Printf("%d %+v\n", &str, (*reflect.StringHeader)(unsafe.Pointer(&str)))
+}
+
+func TestStringAsSlice(t *testing.T) {
+	str := "hello,world"
+	hello := str[:5]
+	world := str[6:]
+	fmt.Printf("%d %+v\n", &str, (*reflect.StringHeader)(unsafe.Pointer(&str)))
+	fmt.Printf("%d %+v\n", &hello, (*reflect.StringHeader)(unsafe.Pointer(&hello)))
+	fmt.Printf("%d %+v\n", &world, (*reflect.StringHeader)(unsafe.Pointer(&world)))
+}
+
+func TestCopy(t *testing.T) {
+	str := "hello,world"
+	fmt.Printf("%d %+v\n", &str, (*reflect.StringHeader)(unsafe.Pointer(&str)))
+	b := []byte(str)
+	fmt.Printf("%d %+v\n", unsafe.Pointer(&b), (*reflect.SliceHeader)(unsafe.Pointer(&b)))
+}
+
+func TestZeroCopy(t *testing.T) {
+	str := "hello,world"
+	fmt.Printf("%d %+v\n", &str, (*reflect.StringHeader)(unsafe.Pointer(&str)))
+	b := unsafe.Slice(unsafe.StringData(str), len(str))
+	fmt.Printf("%s %+v\n", b, (*reflect.SliceHeader)(unsafe.Pointer(&b)))
+}
+
+func TestConvertZeroCopy(t *testing.T) {
+	n := []int64{1, 2, 3, 4}
+	// 注意精度问题
+	fmt.Printf("%+v\n", (*reflect.SliceHeader)(unsafe.Pointer(&n)))
+	f := unsafe.Slice(unsafe.SliceData(n), len(n))
+	fmt.Printf("%v %+v\n", f, (*reflect.SliceHeader)(unsafe.Pointer(&f)))
+}
+
+func TestReplace(t *testing.T) {
+	str := "hello,world"
+	fmt.Printf("%v %+v\n", str, (*reflect.StringHeader)(unsafe.Pointer(&str)))
+	b := []byte(str)
+	b[1] = 'a'
+	str = unsafe.String(unsafe.SliceData(b), len(b))
+	fmt.Printf("%v %+v\n", str, (*reflect.StringHeader)(unsafe.Pointer(&str)))
+}