Closures in array functions in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a closure in PHP?

A closure is an anonymous function that can capture variables from its surrounding scope. It allows you to use variables outside the function inside it.

beginner

How do closures help with array functions like array_map or array_filter?

Closures let you write small, custom functions directly inside array functions to process or filter array elements without defining a separate named function.

intermediate

Explain the use of the 'use' keyword in closures with array functions.

The 'use' keyword lets a closure access variables from the parent scope by copying them into the closure, so you can use external values inside the anonymous function.

beginner

Example: What does this code output?

 $nums = [1, 2, 3];
 $factor = 3;
 $result = array_map(function($n) use ($factor) { return $n * $factor; }, $nums);
 print_r($result); 

It outputs: Array ( [0] => 3 [1] => 6 [2] => 9 ) because the closure multiplies each number by 3 using the captured $factor variable.

intermediate

Why might you prefer closures in array functions over named functions?

Closures keep the code concise and close to where it's used, improving readability and avoiding cluttering the code with many small named functions.

What keyword allows a closure to access variables from outside its own scope in PHP?

A this

B use

C static

D global

The 'use' keyword imports variables from the parent scope into the closure.

Which PHP function commonly uses closures to transform array elements?

A array_push

B array_merge

C array_pop

D array_map

array_map applies a function (often a closure) to each element of an array.

What type of function is a closure in PHP?

A Anonymous function

B Named function

C Recursive function

D Static function

Closures are anonymous functions that can capture variables from outside.

In this code, what is the role of the closure?

array_filter($arr, function($x) { return $x > 10; });

A To filter elements greater than 10

B To add elements to the array

C To sort the array

D To reverse the array

The closure returns true for elements greater than 10, so array_filter keeps those.

What happens if you omit the 'use' keyword when trying to access an external variable inside a closure?

A The variable is automatically global

B The closure can still access the variable

C You get an error or undefined variable inside the closure

D The closure ignores the variable silently

Without 'use', the closure cannot see variables from outside its scope.

Explain how closures work with array functions in PHP and why the 'use' keyword is important.

Think about how you pass extra data into the anonymous function.

Describe a simple example of using a closure with array_map to multiply each element by a factor.

Imagine you have a list of numbers and want to multiply each by 3.