Interface mendefinisikan kontrak — method apa yang harus diimplementasikan. Trait berbagi implementasi antar class.

Interface:

interface Printable {
    public function toString(): string;
}

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

class Invoice implements Printable, Loggable {
    public function toString(): string { return "Invoice #" . $this->id; }
    public function log(): void { logger()->info($this->toString()); }
}

Trait — code reuse tanpa inheritance:

trait HasTimestamps {
    public function getCreatedAt(): string {
        return $this->created_at->format("d M Y");
    }

    public function isRecent(): bool {
        return $this->created_at->isAfter(now()->subDays(7));
    }
}

class Post extends Model {
    use HasTimestamps; // Sekarang Post punya getCreatedAt() dan isRecent()
}

class Comment extends Model {
    use HasTimestamps; // Comment juga!
}

Kapan pakai apa?

• Interface: mendefinisikan APA yang harus bisa dilakukan
• Trait: berbagi BAGAIMANA melakukannya
• Abstract class: keduanya + shared state