Tour of Go 2.0

Creating a slice with make

The built-in make function lets you create a slice with a specific length and capacity — this is how most dynamically-sized slices get created.

make allocates a zeroed array and returns a slice pointing to it:

a := make([]int, 5)  // len(a)=5

Pass a third argument to set the capacity separately from the length:

b := make([]int, 0, 5) // len(b)=0, cap(b)=5
b = b[:cap(b)] // len(b)=5, cap(b)=5
b = b[1:]      // len(b)=4, cap(b)=4

Try it: Experiment with different length/capacity combinations and watch printSlice show how they change.

main.go ▶ Run in Playground 
package main

import "fmt"

func main() {
	a := make([]int, 5)
	printSlice("a", a)

	b := make([]int, 0, 5)
	printSlice("b", b)

	c := b[:2]
	printSlice("c", c)

	d := c[2:5]
	printSlice("d", d)
}

func printSlice(s string, x []int) {
	fmt.Printf("%s len=%d cap=%d %v\n",
		s, len(x), cap(x), x)
}