Go Arrays and Slices

Go Arrays

According to the offical documentation, the type [n]T is an array of n values of type T.

The expression

var a [10]int

declares a variable a as an array of ten integers.

An array’s length is part of its type, so arrays cannot be resized. This seems to be a limitation, but Go seems to provide a way of working with re-size of arrays. I am yet to learn about it. When we come there, will discuss again!

pradeep:~$cat array.go 
package main

import "fmt"

func main() {
	var a [2]string
	a[0] = "Hello"
	a[1] = "World"
	fmt.Println(a[0], a[1])
	fmt.Println(a)

	primes := [6]int{2, 3, 5, 7, 11, 13}
	fmt.Println(primes)
}

pradeep:~$go run array.go 
Hello World
[Hello World]
[2 3 5 7 11 13]

Go Slices

An array has a fixed size. A slice, on the other hand, is a dynamically-sized, flexible view into the elements of an array. In practice, slices are much more common than arrays.

The type []T is a slice with elements of type T.

A slice is formed by specifying two indices, a low and high bound, separated by a colon:

a[low : high]

This selects a half-open range which includes the first element, but excludes the last one.

The following expression creates a slice which includes elements 1 through 3 of a:

a[1:4]

pradeep:~$cat slices.go 
package main

import "fmt"

func main() {
	primes := [6]int{2, 3, 5, 7, 11, 13}

	var s []int = primes[1:4]
	fmt.Println(s)
}

pradeep:~$go run slices.go 
[3 5 7]

A slice does not store any data, it just describes a section of an underlying array.

Changing the elements of a slice modifies the corresponding elements of its underlying array.

Other slices that share the same underlying array will see those changes.

pradeep:~$cat slice-pointers.go 
package main

import "fmt"

func main() {
	names := [4]string{
		"John",
		"Paul",
		"George",
		"Ringo",
	}
	fmt.Println(names)

	a := names[0:2]
	b := names[1:3]
	fmt.Println(a, b)

	b[0] = "XXX"
	fmt.Println(a, b)
	fmt.Println(names)
}

pradeep:~$go run slice-pointers.go 
[John Paul George Ringo]
[John Paul] [Paul George]
[John XXX] [XXX George]
[John XXX George Ringo]
pradeep:~$