Union types in practice in PHP

Introduction

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

When a function can accept either a number or a string as input.

When a variable might hold an integer or a float depending on the situation.

When you want to allow null or a specific type for a parameter.

When working with data that can come in multiple formats, like a string or an array.

When you want to make your code clearer about what types are allowed.

Syntax

PHP

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

Use the pipe character | to separate types.

Union types were introduced in PHP 8.0.

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 an integer or a float and returns a float result.

PHP

function calculate(int|float $number): float {
    return $number * 2;
}

This function accepts a string or null and greets accordingly.

PHP

function greet(string|null $name): void {
    if ($name === null) {
        echo "Hello, guest!";
    } else {
        echo "Hello, $name!";
    }
}

Sample Program

This program shows how a function can accept an integer, string, or null using union types. It prints a message based on the input type.

PHP

<?php

function describeInput(int|string|null $input): void {
    if (is_int($input)) {
        echo "You gave an integer: $input\n";
    } elseif (is_string($input)) {
        echo "You gave a string: $input\n";
    } else {
        echo "You gave nothing (null)\n";
    }
}

describeInput(42);
describeInput("hello");
describeInput(null);

Important Notes

Union types improve code safety by restricting inputs to expected types.

Use is_int(), is_string(), or is_null() to check the actual type inside the function.

Union types cannot be combined with nullable shorthand ?Type if you already use |null.

Summary

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

They help functions accept flexible inputs while keeping code safe.

Check the actual type inside the function to handle each case properly.