What are Class constants:

In PHP, class constants are similar to regular constants but are associated with a specific class. They provide a way to define values that remain constant and do not change throughout the execution of the script. Class constants are accessed using the scope resolution operator :: and are defined using the const keyword.

Declaration of Class Constants:

Class constants are declared within the class using the const keyword followed by the constant name and its value. They must have a visibility modifier (public, protected, or private), and their values must be scalar values (integers, floats, strings, or booleans) or arrays.

<?php

class MyClass {

    const PI = 3.14;

    public const APP_NAME = "MyApp";

    private const MAX_ATTEMPTS = 3;

}

?>

Accessing Class Constants:

Class constants are accessed using the scope resolution operator :: followed by the constant name.

<?php

echo MyClass::PI; // Output: 3.14

echo MyClass::APP_NAME; // Output: MyApp

?>

Visibility of Class Constants:

Class constants can have different visibility modifiers:

public: Accessible from anywhere, both inside and outside the class.

protected: Accessible from within the class and its subclasses (child classes).

private: Accessible only from within the class itself.

Example:

<?php

class Math {

    public const PI = 3.14;

    protected const EULER = 2.718;

    private const GOLDEN_RATIO = 1.618;

}

echo Math::PI; // Output: 3.14

// echo Math::EULER; // This will cause a fatal error because EULER is protected

// echo Math::GOLDEN_RATIO; // This will cause a fatal error because GOLDEN_RATIO is private

Use Cases:

Class constants are useful for defining values that remain constant across instances of a class.

They provide a way to define meaningful names for magic numbers or strings used in the class.

Important Points:

Class constants are associated with the class itself, not with instances of the class.

They provide a way to define global constants within the context of a class.

Class constants are immutable and cannot be modified or redefined after they are declared.

Class constants offer a convenient and organized way to define and access constants within the scope of a class, enhancing code readability and maintainability.