Introduction to PHP Interfaces

PHP Interfaces

An interface defines a contract — a set of method signatures that implementing classes must provide. It enables polymorphism without sharing implementation.

Example

<?php
interface Shape {
    public function area(): float;
    public function perimeter(): float;
    public function describe(): string;
}

class Circle implements Shape {
    public function __construct(private float $radius) {}

    public function area(): float {
        return M_PI * $this->radius ** 2;
    }

    public function perimeter(): float {
        return 2 * M_PI * $this->radius;
    }

    public function describe(): string {
        return "Circle with radius {$this->radius}";
    }
}

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Pro Tip

Interfaces enforce a contract — if a method is missing, PHP raises a fatal error at class definition time.

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