Inheritance

Extend a class

Use extends to reuse a base class in a child class. The child gains all public and protected members of the base.

Details are explained in the guide on inheritance with a longer Animal example.

class Animal { public function voice(): string { return "Sound"; } } class Cat extends Animal { }

Call the parent

A child may override a method and still reuse the original logic. Call parent followed by two colons and the method name.

This pattern keeps shared logic in one place while allowing small changes in children.

class Animal { public function voice(): string { return "Sound"; } } class Cat extends Animal { public function voice(): string { return parent::voice() . " Meow"; } }

public protected private

Visibility controls who can read a property or call a method. Public members are open to all code.

Protected members stay inside the family of parent and children. Private members stay inside one class only.

class Demo { public string $open = "yes"; protected string $family = "yes"; private string $secret = "yes"; }

Abstract classes

An abstract class defines a contract and shares code but cannot be created directly.

Child classes extend it and fill in each abstract method with real logic.

abstract class Shape { abstract public function area(): float; } class Square extends Shape { public function __construct(public float $side = 2.0) { } public function area(): float { return $this->side * $this->side; } }

Next: Interfaces and traits

Article author: Arthur Isaev