slice.go

package main

import (
	"fmt"
	"reflect"
	"unsafe"
)

func main() {
	s := []int{0, 0, 0, 0, 0}
	fmt.Printf("s:\t\t (len %d cap %d data %#x data %v),\t &s:\t %p\n", len(s), cap(s),
		reflect.ValueOf(s).Pointer(), *(*[5]int)(unsafe.Pointer(reflect.ValueOf(s).Pointer())), &s)

	changeLastOne(s)
	fmt.Printf("s changeLastOne: (len %d cap %d data %#x data %v),\t &s:\t %p\n", len(s), cap(s),
		reflect.ValueOf(s).Pointer(), *(*[5]int)(unsafe.Pointer(reflect.ValueOf(s).Pointer())), &s)

	overlay(s)
	fmt.Printf("s overlay:\t (len %d cap %d data %#x data %v),\t &s:\t %p\n", len(s), cap(s),
		reflect.ValueOf(s).Pointer(), *(*[5]int)(unsafe.Pointer(reflect.ValueOf(s).Pointer())), &s)

	replace(s)
	fmt.Printf("s replace:\t (len %d cap %d data %#x data %v),\t &s:\t %p\n", len(s), cap(s),
		reflect.ValueOf(s).Pointer(), *(*[5]int)(unsafe.Pointer(reflect.ValueOf(s).Pointer())), &s)
}

func changeLastOne(slice []int) {
	slice = slice[:cap(slice)]
	slice[len(slice)-1] = -1
}

func overlay(slice []int) {
	fmt.Printf("[overlay] slice: (len %d cap %d data %#x data %v),\t &slice: %p\n", len(slice), cap(slice),
		reflect.ValueOf(slice).Pointer(), *(*[5]int)(unsafe.Pointer(reflect.ValueOf(slice).Pointer())), &slice)
	slice = []int{1, 2, 3, 4, 5}
	fmt.Printf("[overlay] slice: (len %d cap %d data %#x data %v),\t &slice: %p\n", len(slice), cap(slice),
		reflect.ValueOf(slice).Pointer(), *(*[5]int)(unsafe.Pointer(reflect.ValueOf(slice).Pointer())), &slice)
}

func replace(slice []int) {
	fmt.Printf("[replace] slice: (len %d cap %d data %#x data %v),\t &slice: %p\n", len(slice), cap(slice),
		reflect.ValueOf(slice).Pointer(), *(*[5]int)(unsafe.Pointer(reflect.ValueOf(slice).Pointer())), &slice)
	slice[2] = 1
	fmt.Printf("[replace] slice: (len %d cap %d data %#x data %v),\t &slice: %p\n", len(slice), cap(slice),
		reflect.ValueOf(slice).Pointer(), *(*[5]int)(unsafe.Pointer(reflect.ValueOf(slice).Pointer())), &slice)
}