Readonly classes in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a readonly class in PHP?

A readonly class in PHP is a class where all properties are automatically readonly, meaning their values can only be set once, typically during object construction, and cannot be changed afterwards.

beginner

How do you declare a readonly class in PHP?

You declare a readonly class by adding the <code>readonly</code> keyword before the <code>class</code> keyword, like this: <code>readonly class MyClass {}</code>.

beginner

Can you modify properties of a readonly class after the object is created?

No, properties of a readonly class cannot be modified after the object is created. They are set once during construction and then become immutable.

intermediate

What happens if you try to change a property of a readonly class after construction?

PHP will throw an Error if you try to modify a property of a readonly class after the object has been constructed, enforcing immutability.

intermediate

Why use readonly classes in PHP?

Readonly classes help create immutable objects, which can make code safer and easier to understand by preventing accidental changes to object state after creation.

How do you declare a readonly class in PHP?

A class readonly MyClass {}

B readonly class MyClass {}

C class MyClass readonly {}

D readonly MyClass class {}

The correct syntax is to place the readonly keyword before class: readonly class MyClass {}.

What happens if you try to change a property of a readonly class after construction?

A The property changes successfully.

B The property resets to default.

C The property silently ignores the change.

D PHP throws an Error.

Readonly properties cannot be changed after construction; PHP throws an Error to enforce this.

When are readonly properties set in a readonly class?

A Only inside methods.

B Anytime after construction.

C Only during object construction.

D They cannot be set at all.

Readonly properties are set once during object construction and cannot be changed later.

What is a key benefit of using readonly classes?

A Improves code safety by making objects immutable.

B Allows properties to be changed anytime.

C Makes code run faster.

D Enables dynamic property creation.

Readonly classes create immutable objects, which helps prevent accidental changes and improves code safety.

Can a readonly class have non-readonly properties?

A No, all properties are readonly automatically.

B Only private properties can be writable.

C Only static properties can be writable.

D Yes, some properties can be writable.

In a readonly class, all properties are automatically readonly; you cannot have writable properties.

Explain what a readonly class is and how it affects object properties in PHP.

Think about how readonly classes make objects unchangeable after creation.

Describe the benefits of using readonly classes in your PHP code.

Consider why keeping object data fixed can help avoid bugs.