PHP OOP Composition vs Inheritance

The feature illustrated below operates on PHP values, objects, or language metadata.

What Is OOP Composition vs Inheritance in PHP?

Interfaces define contracts, inheritance specializes related types, and composition delegates responsibilities to collaborators.

Example 1: Understanding the Basic Behavior

<?php

interface Reporter { public function report(): string; }
class JsonReporter implements Reporter { public function report(): string { return '{"ok":true}'; } }
echo (new JsonReporter())->report();

Output:

{"ok":true}

Explanation: Interfaces define contracts, inheritance specializes related types, and composition delegates responsibilities to collaborators.

Example 2: Testing Another Case

<?php

class Logger { public function write(string $message): void { echo $message; } }
class Worker { public function __construct(private Logger $logger) {} public function run(): void { $this->logger->write('working'); } }
(new Worker(new Logger()))->run();

Output:

working

Explanation: Composition delegates behavior to collaborators, while inheritance establishes an is-a relation to a parent type.

Practical Example: Applying the Operation

<?php

abstract class Payment { abstract public function label(): string; }
class CardPayment extends Payment { public function label(): string { return 'Card'; } }
echo (new CardPayment())->label();

Output:

Card

Explanation: Extending a parent solely for implementation reuse can create fragile coupling; prefer injecting a collaborator when behavior varies independently.

Important Behavior and Edge Cases

• Composition delegates behavior to collaborators, while inheritance establishes an is-a relation to a parent type.
• Extending a parent solely for implementation reuse can create fragile coupling; prefer injecting a collaborator when behavior varies independently.

Comparison With Related Approaches

Common Beginner Mistakes

Key Takeaways

• Interfaces define contracts, inheritance specializes related types, and composition delegates responsibilities to collaborators.
• Composition delegates behavior to collaborators, while inheritance establishes an is-a relation to a parent type.
• Extending a parent solely for implementation reuse can create fragile coupling; prefer injecting a collaborator when behavior varies independently.

The examples demonstrate where OOP Composition vs Inheritance fits within php programming. Verify the relevant preconditions whenever you adapt the code to real data.