Anonymous function syntax in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of an anonymous function assigned to a variable

What is the output of this PHP code?

PHP

<?php
$greet = function($name) {
    return "Hello, $name!";
};
echo $greet("Alice");
?>

A Error: Undefined variable $name

B Hello, $name!

C Hello, Alice!

D Hello, !

💡 Hint

Look at how the anonymous function uses the parameter inside the string.

The anonymous function takes a parameter $name and returns a greeting string with that name. When called with "Alice", it outputs "Hello, Alice!".

❓ Predict Output

intermediate

Using 'use' keyword to access external variable

What will this PHP code output?

PHP

<?php
$message = "Hi";
$func = function($name) use ($message) {
    return "$message, $name!";
};
echo $func("Bob");
?>

A Hi, $name!

B Hi, Bob!

C Error: Undefined variable $message

D Hi!

💡 Hint

Check how the 'use' keyword brings $message inside the function.

The 'use' keyword imports the external variable $message into the anonymous function's scope. So it outputs "Hi, Bob!".

🔧 Debug

advanced

Identify the error in anonymous function syntax

What error does this PHP code produce?

PHP

<?php
$func = function($x) {
    return $x * 2
};
echo $func(5);
?>

A Parse error: syntax error, unexpected '}', expecting ';'

B Fatal error: Call to undefined function function()

C Warning: Missing argument for function

D No error, outputs 10

💡 Hint

Check the line before the closing brace for missing punctuation.

The function body is missing a semicolon after 'return $x * 2'. This causes a syntax error before the closing brace.

❓ Predict Output

advanced

Anonymous function modifying external variable by reference

What is the output of this PHP code?

PHP

<?php
$count = 0;
$increment = function() use (&$count) {
    $count++;
};
$increment();
$increment();
echo $count;
?>

A 0

B Error: Cannot use variable by reference

C 1

D 2

💡 Hint

Look at how the variable is passed by reference with &.

The anonymous function uses &$count to modify the external variable directly. Calling it twice increments count to 2.

🧠 Conceptual

expert

Understanding closure binding in anonymous functions

Given this PHP code, what will be the output?

PHP

<?php
class Counter {
    private int $count = 0;
    public function getIncrementer() {
        return function() {
            $this->count++;
            return $this->count;
        };
    }
}

$counter = new Counter();
$inc = $counter->getIncrementer();
echo $inc();
echo $inc();
?>

A 12

B 01

C Error: Using $this in anonymous function without binding

D 11

💡 Hint

Anonymous functions inside classes can access $this if called correctly.

The anonymous function is a closure that inherits $this from the Counter object. Each call increments $this->count and returns the new value, so it outputs 1 followed by 2, resulting in "12".