Closures and variable binding with use 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, allowing it to use those variables even when called outside that scope.

beginner

How does the use keyword work in PHP closures?

The use keyword lets a closure access variables from the parent scope by copying their values into the closure's scope.

intermediate

What happens if you modify a variable inside a closure without use?

Without use, the closure cannot access or modify variables from the parent scope. Variables inside the closure are local and separate.

intermediate

How can you modify a variable from the parent scope inside a closure?

You can pass the variable by reference using use (&$var). This allows the closure to change the original variable's value.

intermediate

Explain the difference between passing variables by value and by reference in closures.

Passing by value copies the variable's value into the closure, so changes inside don't affect the original. Passing by reference shares the variable, so changes inside the closure update the original variable.

What does the use keyword do in a PHP closure?

A Declares a global variable inside the closure

B Defines the return type of the closure

C Allows the closure to access variables from the parent scope

D Creates a new variable inside the closure

The use keyword lets the closure access variables from the parent scope by copying or referencing them.

How do you allow a closure to modify a variable from the parent scope?

A Declare the variable as global inside the closure

B Pass the variable by reference using <code>use (&$var)</code>

C Use <code>global $var</code> outside the closure

D You cannot modify parent variables inside closures

Passing the variable by reference with use (&$var) allows the closure to modify the original variable.

What happens if you omit use when trying to access a parent variable inside a closure?

A The variable is treated as a global variable

B The closure automatically accesses the variable

C The variable is copied by default

D The closure cannot access the variable and will cause an error

Without use, the closure does not have access to variables from the parent scope and will cause an error if you try to use them.

Which of the following is a correct way to create a closure that uses a variable $x from the parent scope?

A function() use ($x) { return $x * 2; }

B function($x) { return $x * 2; }

C function() { return $x * 2; }

D function() global $x { return $x * 2; }

Using use ($x) correctly imports the variable $x into the closure's scope.

If you want to keep the original variable unchanged, how should you pass it to a closure?

A Pass it by value using <code>use ($var)</code>

B Pass it by reference using <code>use (&$var)</code>

C Declare it as global inside the closure

D You cannot keep it unchanged

Passing by value copies the variable, so changes inside the closure do not affect the original.

Explain how the use keyword works with closures in PHP and why it is needed.

Think about how closures get variables from outside their own function.

Describe the difference between passing variables by value and by reference in PHP closures and give an example of when to use each.

Consider if you want the closure to change the original variable or not.