Inheritance

Inheritance

Inheritance, parent and Late Static Binding

A child class extends one parent, inherits its public and protected members, and may override methods with compatible signatures; parent:: calls the overridden version. self:: binds to the class where it is written, static:: to the class actually called: late static binding.

parent::, self:: versus static::, and new staticPHP

<?php
class Product {
  public function __construct(public string $title) {}
  public static function create(string $title): static { return new static($title); }
  public static function kindSelf(): string { return self::kind(); }      // where written
  public static function kindStatic(): string { return static::kind(); }  // who was called
  protected static function kind(): string { return 'product'; }
}
class Ebook extends Product {
  public function __construct(string $title, public float $sizeMb = 2.5) {
    parent::__construct($title);                  // run the parent's constructor
  }
  protected static function kind(): string { return 'ebook'; }   // override
}
$e = Ebook::create('Dune');                       // inherited, yet builds an Ebook
echo get_class($e), " {$e->title} {$e->sizeMb} MB | ";
echo Ebook::kindSelf(), ' vs ', Ebook::kindStatic(), "\n";

Output

Ebook Dune 2.5 MB | product vs ebook

Use self:: when subclasses must not redirect a call, static:: when they should. Share behavior across unrelated classes with Interfaces and Generators's interfaces and traits or with composition (Subsection 4.9.14).

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