الأنماط الإنشائية: Factory وBuilder وSingleton

التحكم في الإنشاء

المصنع البسيط

<?php
interface Notifier { public function send(string $msg): string; }
final class EmailNotifier implements Notifier {
    public function send(string $m): string { return "email: $m"; }
}
final class SmsNotifier implements Notifier {
    public function send(string $m): string { return "sms: $m"; }
}

final class NotifierFactory {
    public static function make(string $channel): Notifier {
        return match ($channel) {
            'email' => new EmailNotifier(),
            'sms'   => new SmsNotifier(),
            default => throw new InvalidArgumentException($channel),
        };
    }
}
echo NotifierFactory::make('sms')->send('Hi'), PHP_EOL;

طريقة المصنع

<?php
abstract class ReportExporter {
    abstract protected function create(): string;
    public function export(): string {
        return 'Exported as ' . $this->create();
    }
}
final class PdfExporter extends ReportExporter {
    protected function create(): string { return 'PDF'; }
}
final class CsvExporter extends ReportExporter {
    protected function create(): string { return 'CSV'; }
}
echo (new PdfExporter())->export(), PHP_EOL;
echo (new CsvExporter())->export(), PHP_EOL;

المصنع المجرّد

الباني: المشكلة

الباني بطلاقة

<?php
final class Query {
    public function __construct(public readonly string $sql) {}
}
final class QueryBuilder {
    private string $table = '';
    private array $where = [];
    public function from(string $t): self { $this->table = $t; return $this; }
    public function where(string $c): self { $this->where[] = $c; return $this; }
    public function build(): Query {
        $sql = "SELECT * FROM {$this->table}";
        if ($this->where) { $sql .= ' WHERE ' . implode(' AND ', $this->where); }
        return new Query($sql);
    }
}
echo (new QueryBuilder())->from('users')->where('age > 18')->build()->sql, PHP_EOL;

الباني مقارنةً بالمنشئات المسمّاة

<?php
final class Money {
    private function __construct(public readonly int $cents, public readonly string $cur) {}
    public static function fromDollars(float $d): self {
        return new self((int) round($d * 100), 'USD');
    }
    public static function zero(string $cur = 'USD'): self {
        return new self(0, $cur);
    }
}
var_dump(Money::fromDollars(19.99)->cents); // int(1999)

Singleton

<?php
final class Config {
    private static ?self $instance = null;
    private array $data = ['debug' => true];
    private function __construct() {}
    public static function instance(): self {
        return self::$instance ??= new self();
    }
    public function get(string $k): mixed { return $this->data[$k] ?? null; }
}
var_dump(Config::instance()->get('debug'));
var_dump(Config::instance() === Config::instance()); // true

لماذا يسبب Singleton مشكلات

اختيار الأداة المناسبة

مصنع قائم على السجل

<?php
interface Shape { public function name(): string; }
final class Circle implements Shape { public function name(): string { return 'circle'; } }
final class Square implements Shape { public function name(): string { return 'square'; } }

final class ShapeRegistry {
    private array $creators = [];
    public function register(string $key, callable $factory): void {
        $this->creators[$key] = $factory;
    }
    public function create(string $key): Shape {
        return ($this->creators[$key] ?? throw new InvalidArgumentException($key))();
    }
}
$r = new ShapeRegistry();
$r->register('circle', fn() => new Circle());
$r->register('square', fn() => new Square());
echo $r->create('square')->name(), PHP_EOL; // square

فحص سريع

مراجعة