PHP — Interfaces

Basic interface

<?php
interface Drawable {
    public function draw(): string;
}

class Circle implements Drawable {
    public function draw(): string {
        return "Drawing circle";
    }
}

$circle = new Circle();
echo $circle->draw(); // Drawing circle
?>

Multiple interfaces

<?php
interface Printable {
    public function print(): string;
}

interface Loggable {
    public function log(): string;
}

class Document implements Printable, Loggable {
    public function print(): string {
        return "Printing document";
    }

    public function log(): string {
        return "Logging document";
    }
}
?>

Interface constants

<?php
interface Config {
    const MAX_RETRIES = 3;
    const TIMEOUT = 30;
}

echo Config::MAX_RETRIES; // 3
?>

Interface inheritance

<?php
interface Loggable {
    public function log(): string;
}

interface AuditLoggable extends Loggable {
    public function audit(): string;
}
?>

Type hints with interfaces

<?php
interface Repository {
    public function find(int $id): array;
    public function save(array $data): bool;
}

class UserRepository implements Repository {
    public function find(int $id): array {
        return ['id' => $id, 'name' => 'Alice'];
    }

    public function save(array $data): bool {
        return true;
    }
}

function process(Repository $repo): void {
    $user = $repo->find(1);
    echo $user['name'];
}

$repo = new UserRepository();
process($repo);
?>

Mini Practice

Write PHP code that:

1. Defines an interface with methods
2. Implements multiple interfaces
3. Uses an interface for type hints
4. Creates interface constants

Up Next

In the next lesson, you'll learn about Traits — code reuse in PHP.