How to check if a slice contains an element in Go

The Go 1.21 release, which is scheduled for August 2023, includes a new package called slices. This package provides a set of generic functions that work with slices of any type. One of the most useful functions in the slices package is Contains(), which checks if an element of the slice is present or not.

The Contains() function takes two arguments: the first argument is the slice, and the second argument is the element that you want to check for. The function returns a boolean value, indicating whether or not the element is present in the slice.

Here is an example of how to use this function in your Go programs:

package main

import (
	"slices"
)

func main() {
	numbers := []int{0, 42, 10, 8}
	containsTen := slices.Contains(numbers, 10) // true
	containsTwo := slices.Contains(numbers, 2) // false
}

Using the x/exp/slices package

The x/exp/slices package is an experimental package initially released for Go 1.18 and later developed into the slices package in Go 1.21. While it does not provide all the functionality in the final slices package, the Contains() function demonstrated above is present and works the same way. You only need to install the package first:

go get golang.org/x/exp/slices

Then import it into your program like this:

package main

import (
	"golang.org/x/exp/slices"
)

. . .

Go 1.17 and earlier

Since Go 1.17 and earlier releases do not support generics, you need to write your own function to check if a slice contains an element in Go. Unfortunately, you need to do this for each slice type that requires this functionality. Here’s an example showcasing how to implement this for a slice of strings:

// https://play.golang.org/p/Qg_uv_inCek
// contains checks if a string is present in a slice
func contains(s []string, str string) bool {
	for _, v := range s {
		if v == str {
			return true
		}
	}

	return false
}

func main() {
	s := []string{"James", "Wagner", "Christene", "Mike"}
	fmt.Println(contains(s, "James")) // true
	fmt.Println(contains(s, "Jack")) // false
}

The contains function above iterates over the string slice and compares each value to the string from the second parameter. If the value is found, true is returned and the function exits. Otherwise, if the value is not found, false is returned.

Fortunately, the release of Go 1.18 makes writing these functions unnecessary, so ensure that you upgrade to the latest version as soon as possible.

Thanks for reading, and happy coding!

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