Polymorphism in PHP

Polymorphism lets code consume an interface while multiple implementations provide behavior.

What It Does

Polymorphism lets code consume an interface while multiple implementations provide behavior. The following examples distinguish a normal use case, a boundary case and a practical application.

Requirements and Compatibility

PHP 8.x and a local test environment. Apply input validation, correct error handling and the requirements of any optional libraries.

The code focuses on the core concept. Production implementation may also need routes, validation, persistence, authorization or deployment tooling.

Example 1: Basic Behavior

Start with the smallest meaningful working case.

<?php
interface Formatter { public function format(string $text): string; }
class UpperFormatter implements Formatter { public function format(string $text): string { return strtoupper($text); } }
echo (new UpperFormatter())->format('hello');

Example 2: Another Case

Examine the edge case and the observable result.

<?php
interface Charge { public function amount(): int; }
class FlatCharge implements Charge { public function amount(): int { return 40; } }
function showCharge(Charge $charge): int { return $charge->amount(); }
echo showCharge(new FlatCharge());

Practical Example: Putting It to Use

Apply the technique to a small practical task.

<?php
abstract class Notifier { abstract public function send(string $message): string; }
class LogNotifier extends Notifier { public function send(string $message): string { return '[log]' . $message; } }
echo (new LogNotifier())->send('Ready');

Important Behavior and Edge Cases

Do not replace clear composition with deep subclass chains just to share a small method.

Comparison with Related Functions or Approaches

Common Beginner Mistakes

Key Takeaways

• Polymorphism lets code consume an interface while multiple implementations provide behavior.
• Do not replace clear composition with deep subclass chains just to share a small method.
• Dependency injection makes polymorphic implementations testable.

Before adapting these examples, verify the return values, test the failure paths and confirm that your application meets its security and environment requirements.