Closures as callbacks in PHP - Mini Project: Build & Apply

Closures as callbacks

📖 Scenario: You are building a simple PHP program that processes a list of numbers. You want to apply different operations to each number using functions that you can pass around easily.

🎯 Goal: Learn how to create and use closures (anonymous functions) as callbacks in PHP to process an array of numbers.

📋 What You'll Learn

Create an array of numbers

Create a closure (anonymous function) to double a number

Use the closure as a callback to process the array

Print the processed array

💡 Why This Matters

🌍 Real World

Closures as callbacks are useful when you want to pass small pieces of code to functions for flexible processing, like transforming data or filtering lists.

💼 Career

Understanding closures and callbacks is important for PHP developers working with array functions, event handlers, or asynchronous code.

1

Create the numbers array

Create an array called numbers with these exact values: 1, 2, 3, 4, 5.

PHP

<?php

// Create the array called numbers with values 1, 2, 3, 4, 5
// Your code here

Need a hint?

Use square brackets [] to create an array in PHP.

2

Create a closure to double a number

Create a closure called double that takes one parameter $n and returns $n * 2.

PHP

<?php

$numbers = [1, 2, 3, 4, 5];

// Create a closure called double that doubles its input
// Your code here

Need a hint?

Use function($n) { return $n * 2; }; to create the closure.

3

Use the closure as a callback to process the array

Use the array_map function with the double closure to create a new array called doubledNumbers.

PHP

<?php

$numbers = [1, 2, 3, 4, 5];

$double = function($n) {
    return $n * 2;
};

// Use array_map with double to create doubledNumbers
// Your code here

Need a hint?

Use array_map($double, $numbers) to apply the closure to each element.

4

Print the processed array

Print the doubledNumbers array using print_r.

PHP

<?php

$numbers = [1, 2, 3, 4, 5];

$double = function($n) {
    return $n * 2;
};

$doubledNumbers = array_map($double, $numbers);

// Print the doubledNumbers array
// Your code here

Need a hint?

Use print_r($doubledNumbers); to display the array.