slices-in-go.go

package main

// Example explaining how slices works
// About slice's capacity, pointers and copies

import "fmt"

func main() {

	// let's create slice with len 2 and capacity 3
	sl := make([]int, 2, 3)
	fmt.Println("slice sl cap=", cap(sl))

	// if you need pointer to slice data make it explicit
	psl := &sl

	// set value to first slice element
	sl[0] = 11
	fmt.Println("slice sl and pointer to it psl", sl, psl)

	// this is how you can change original slice through pointer
	(*psl)[0] = 21

	fmt.Println("original slice element sl[0] changed through pointer (*psl)[0]", sl)

	// add more data then capacity of original slice
	// new memory block will be allocated to hold new values
	// capacity will double
	sl = append(sl, []int{2, 3, 4}...)
	fmt.Println("sl cap increased after append cap =", cap(sl))

	// if you need copy slice make it explicitly
	// first prepare slice where to copy
	csl := make([]int, len(sl))

	// now copy from original slice to new slice which will hold data
	copy(csl, sl)

	// try to change slice copy, it will not change original slice
	csl[0] = 77
	fmt.Println("slice sl, pointer to slice psl and copy of slice csl", sl, psl, csl)

}