Nullable types in functions in PHP - Mini Project: Build & Apply

Nullable types in functions

📖 Scenario: You are building a simple PHP program that handles user profiles. Sometimes, the user may not provide their middle name, so your function should accept a nullable string for the middle name.

🎯 Goal: Create a PHP function that accepts a nullable string parameter for the middle name and returns a greeting message that includes the middle name if provided, or a default message if not.

📋 What You'll Learn

Create a function called greetUser that accepts a nullable string parameter called $middleName

Inside the function, check if $middleName is null

Return a greeting message that includes the middle name if it is not null

Return a different greeting message if $middleName is null

Call the function twice: once with a middle name and once with null

Print the results of both function calls

💡 Why This Matters

🌍 Real World

Nullable types are common when dealing with optional user input, like middle names or phone numbers, where the value might be missing.

💼 Career

Understanding nullable types helps you write safer PHP functions that handle missing or optional data without errors.

1

Create the function with a nullable parameter

Write a PHP function called greetUser that accepts one parameter ?string $middleName. The function should start with an empty body.

PHP

<?php

// Define the function greetUser with nullable string parameter $middleName
function greetUser(?string $middleName) {
    // Your code here
}

Need a hint?

Use ?string before the parameter name to make it nullable.

2

Add a variable for the default message

Inside the greetUser function, create a variable called $defaultMessage and set it to the string 'Hello, guest!'.

PHP

<?php

function greetUser(?string $middleName) {
    // Create a variable $defaultMessage with value 'Hello, guest!'
    // Your code here
}

Need a hint?

Assign the string 'Hello, guest!' to the variable $defaultMessage.

3

Add logic to return greeting based on nullable parameter

Inside the greetUser function, write an if statement to check if $middleName is not null. If it is not null, return the string 'Hello, ' . $middleName . '!'. Otherwise, return the $defaultMessage.

PHP

<?php

function greetUser(?string $middleName) {
    $defaultMessage = 'Hello, guest!';
    // Add if statement to check if $middleName is not null
    // Return greeting with middle name or default message
    // Your code here
}

Need a hint?

Use if ($middleName !== null) to check if the parameter has a value.

4

Call the function and print the results

Call the greetUser function twice: once with the argument 'James' and once with null. Print both results using echo with a newline after each.

PHP

<?php

function greetUser(?string $middleName) {
    $defaultMessage = 'Hello, guest!';
    if ($middleName !== null) {
        return 'Hello, ' . $middleName . '!';
    } else {
        return $defaultMessage;
    }
}

// Call greetUser with 'James' and print the result
// Call greetUser with null and print the result
// Your code here

Need a hint?

Use echo to print the returned strings with a newline "\n" after each.