Abstract Constants

By WebSmithery

<?php

abstract class Foo {
    
    // self-referential 'abstract' declaration
    const NAME = self::NAME;
}

class Fooling extends Foo {
    
    // Overrides definition from parent class
    // Without this declaration, an error will be triggered
    const NAME = 'Donald';
}

There’s a pretty common pattern to declare “abstract class constants” in PHP.

PHP lazy loading will prevent the error “Fatal error: Uncaught Error: Cannot declare self-referencing constant self::NAME” if the constant is overloaded.

This makes an effective ‘abstract constant’, that must be defined to be usable.

See Also

• Class Constants (PHP manual)
• Class Abstraction (PHP manual)
• Abstract constants in PHP - Force a child class to define a constant
• Abstract Class Constant on 3v4l.org [Try me]

PHP Features

• abstract
• class-constant
• self
• inheritance
• lazy-loading

Last updated: 10 September 2026