Arrow functions (short closures) in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple arrow function

What is the output of the following PHP code using an arrow function?

PHP

<?php
$multiplier = 3;
$numbers = [1, 2, 3];
$results = array_map(fn($n) => $n * $multiplier, $numbers);
print_r($results);
?>

A Array ( [0] => 3 [1] => 6 [2] => 9 )

B Array ( [0] => 1 [1] => 2 [2] => 3 )

C Array ( [0] => 0 [1] => 0 [2] => 0 )

D Fatal error: Uncaught Error: Undefined variable: multiplier

💡 Hint

Remember that arrow functions automatically capture variables from the parent scope.

The arrow function multiplies each number by the multiplier variable from the outer scope, producing 3, 6, and 9.

❓ Predict Output

intermediate

Arrow function with multiple parameters

What will this PHP code output?

PHP

<?php
$adder = fn($a, $b) => $a + $b;
echo $adder(5, 7);
?>

A Error: Too few arguments

B 57

C 12

D Error: Syntax error

💡 Hint

Arrow functions can take multiple parameters just like normal functions.

The arrow function adds 5 and 7, outputting 12.

🔧 Debug

advanced

Why does this arrow function cause an error?

Consider this PHP code snippet. What error will it produce and why?

PHP

<?php
$factor = 2;
$func = fn($x) => $x * $factor;
$factor = 'three';
echo $func(4);
?>

A Outputs 12 because arrow functions use the variable's value at call time

B Outputs 8 because arrow functions capture variables by value at definition time

C Fatal error: Cannot use string 'three' as a number

D Parse error: syntax error

💡 Hint

Arrow functions capture variables from the parent scope by value, not by reference.

Arrow functions capture variables by value when defined, so $factor is 2 inside the function even if changed later.

📝 Syntax

advanced

Identify the syntax error in arrow function usage

Which option contains a syntax error in the arrow function?

A $f = fn($x) => $x + 1;

B $f = fn($x) => $x * 2;

C $f = fn($x) { return $x * 2; };

D $f = fn($x) => { $x * 2; };

💡 Hint

Arrow functions must have a single expression without braces or use return inside braces in normal closures.

Option D uses braces with an arrow function but does not return a value, causing a syntax error.

🚀 Application

expert

Using arrow functions to filter and transform arrays

Given the array $nums = [1, 2, 3, 4, 5, 6], which option produces an array of squares of even numbers only?

PHP

<?php
$nums = [1, 2, 3, 4, 5, 6];
// Your code here
?>

A array_map(fn($n) => $n * $n, array_filter($nums, fn($n) => $n % 2 === 0));

B ;)0 ==! 2 % n$ >= )n$(nf ,)smun$ ,n$ * n$ >= )n$(nf(pam_yarra(retlif_yarra

C array_map(fn($n) => $n * $n, array_filter($nums, fn($n) => $n % 2));

D array_filter(array_map(fn($n) => $n * $n, $nums), fn($n) => $n % 2 !== 0);

💡 Hint

Filter first to keep even numbers, then map to square them.

Option A filters even numbers first, then squares them, producing [4, 16, 36]. Others either filter odd numbers or filter after mapping incorrectly.