Nullable types in functions in PHP

Introduction

Nullable types let a function accept either a specific type or null. This helps when a value might be missing or optional.

When a function parameter can be a number or no value at all.

When a function should return a string or nothing (null).

When you want to clearly say a value can be empty or a certain type.

When working with optional settings or inputs in your code.

Syntax

PHP

function functionName(?TypeName $param): ?ReturnType {
    // function body
}

The ? before a type means it can be that type or null.

You can use nullable types for both parameters and return values.

Examples

This function accepts a string or null. It greets a guest if no name is given.

PHP

<?php
function greet(?string $name): void {
    if ($name === null) {
        echo "Hello, guest!\n";
    } else {
        echo "Hello, $name!\n";
    }
}

This function returns a string username or null if not found.

PHP

<?php
function findUser(int $id): ?string {
    if ($id === 1) {
        return "Alice";
    }
    return null;
}

Sample Program

This program shows how a function uses a nullable integer parameter to describe age or say it's unknown.

PHP

<?php
function describeAge(?int $age): string {
    if ($age === null) {
        return "Age is unknown.";
    }
    return "Age is $age years.";
}

echo describeAge(25) . "\n";
echo describeAge(null) . "\n";

Important Notes

Nullable types help avoid errors when values might be missing.

Remember to check for null inside the function before using the value.

Summary

Nullable types allow null or a specific type in functions.

Use ? before the type to make it nullable.

Check for null inside your function to handle missing values safely.