Readonly properties in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a readonly property in PHP?

A readonly property is a class property that can only be assigned once, typically during object construction, and cannot be changed afterward.

beginner

How do you declare a readonly property in PHP?

You declare a readonly property by adding the readonly keyword before the property type and name inside a class.

beginner

Can you assign a value to a readonly property outside the constructor in PHP?

No, once a readonly property is assigned a value (usually in the constructor), it cannot be changed later anywhere else in the code.

intermediate

What happens if you try to modify a readonly property after it has been set?

PHP will throw an error because readonly properties are immutable after their initial assignment.

beginner

Why use readonly properties in PHP classes?

Readonly properties help protect data by preventing accidental changes, making objects more predictable and safer to use.

How do you declare a readonly property in PHP?

A Use the keyword <code>readonly</code> before the property name

B Use the keyword <code>const</code> before the property name

C Use the keyword <code>final</code> before the property name

D Use the keyword <code>static</code> before the property name

Readonly properties are declared using the readonly keyword before the property name.

When can you assign a value to a readonly property?

A Only after the object is destroyed

B Multiple times anywhere in the class

C Only once, typically in the constructor

D Only inside static methods

Readonly properties can be assigned only once, usually during object construction.

What happens if you try to change a readonly property after it is set?

A PHP throws an error

B The property value changes silently

C The property resets to null

D The program ignores the change

PHP throws an error because readonly properties cannot be modified after initial assignment.

Which PHP version introduced readonly properties?

A PHP 8.0

B PHP 8.1

C PHP 7.4

D PHP 7.0

Readonly properties were introduced in PHP 8.1.

Why are readonly properties useful?

A They make properties private

B They make properties static

C They allow properties to be changed anytime

D They prevent accidental changes to important data

Readonly properties help keep data safe by preventing accidental changes.

Explain what readonly properties are and how they work in PHP.

Think about properties that you set once and then keep safe.

Describe a situation where using readonly properties would be helpful in a PHP program.

Consider data that should never change after creation.