Union types in PHP

Introduction

Union types let you say a value can be one of several types. This helps your code accept different kinds of data safely.

When a function can accept more than one type of input, like a number or a string.

When a variable might hold different types at different times.

When you want to be clear about all possible types a value can have.

When you want to avoid errors by checking types before using values.

Syntax

PHP

function example(int|string $value): void {
    // code here
}

Use the pipe symbol | to separate types.

Union types are supported in PHP 8.0 and later.

Examples

This function accepts either an integer or a string and prints it.

PHP

function printValue(int|string $value): void {
    echo $value;
}

This function accepts a string or an array and returns its length.

PHP

function getLength(string|array $input): int {
    return is_string($input) ? strlen($input) : count($input);
}

Using mixed is a broader type, but union types are more specific.

PHP

function process(mixed $data): void {
    if (is_int($data) || is_string($data)) {
        echo "Data is int or string: $data";
    }
}

Sample Program

This program defines a function that accepts either an integer or a string. It checks the type and prints a message accordingly.

PHP

<?php

function describeValue(int|string $value): void {
    if (is_int($value)) {
        echo "Integer: $value\n";
    } else {
        echo "String: $value\n";
    }
}

describeValue(10);
describeValue("hello");

Important Notes

Union types improve code clarity and reduce bugs by enforcing allowed types.

Nullable types like ?int can be written as int|null with union types.

Union types cannot contain duplicate types or void.

Summary

Union types let a value be one of several types using the | symbol.

They help functions and variables accept multiple types safely.

Supported from PHP 8.0 onwards.