振る舞いパターン：Strategy、Observer、Command

振る舞いをモデル化する

Strategy：考え方

<?php
// The smell Strategy removes: branching on a type code
function price(string $type, float $base): float {
    switch ($type) {
        case 'standard': return $base + 5;
        case 'express':  return $base + 15;
        default: throw new InvalidArgumentException($type);
    }
}
echo price('express', 10), PHP_EOL; // 25

コードで見るStrategy

<?php
interface ShippingStrategy { public function cost(float $weight): float; }
final class Standard implements ShippingStrategy {
    public function cost(float $w): float { return 5 + $w * 0.5; }
}
final class Express implements ShippingStrategy {
    public function cost(float $w): float { return 15 + $w * 1.2; }
}

final class Cart {
    public function __construct(private ShippingStrategy $strategy) {}
    public function setStrategy(ShippingStrategy $s): void { $this->strategy = $s; }
    public function quote(float $weight): float { return $this->strategy->cost($weight); }
}

$cart = new Cart(new Standard());
echo $cart->quote(10), PHP_EOL;     // 10
$cart->setStrategy(new Express());
echo $cart->quote(10), PHP_EOL;     // 27

クロージャーを使ったStrategy

<?php
$strategies = [
    'asc'  => fn(array $a) => sort($a) ? $a : $a,
    'desc' => fn(array $a) => rsort($a) ? $a : $a,
];
$data = [3, 1, 2];
print_r($strategies['desc']($data)); // [3,2,1]

Observer：考え方

コードで見るObserver

<?php
interface Observer { public function update(string $event): void; }

final class OrderSubject {
    private array $observers = [];
    public function subscribe(Observer $o): void { $this->observers[] = $o; }
    public function placed(string $id): void {
        foreach ($this->observers as $o) { $o->update("order $id placed"); }
    }
}
final class EmailObserver implements Observer {
    public function update(string $e): void { echo "email: $e" . PHP_EOL; }
}
final class AuditObserver implements Observer {
    public function update(string $e): void { echo "audit: $e" . PHP_EOL; }
}

$subject = new OrderSubject();
$subject->subscribe(new EmailObserver());
$subject->subscribe(new AuditObserver());
$subject->placed('42');

ObserverとPSR-14

Command：考え方

<?php
final class SendEmail {
    public function __construct(
        public readonly string $to,
        public readonly string $subject
    ) {}
}
// The request is now data you can store, serialize, or enqueue
$cmd = new SendEmail('user@example.com', 'Welcome');
echo json_encode($cmd), PHP_EOL;

コードで見るCommand

<?php
interface Command { public function execute(): string; }

final class Light { public bool $on = false; }
final class TurnOn implements Command {
    public function __construct(private Light $light) {}
    public function execute(): string { $this->light->on = true; return 'light on'; }
}
final class TurnOff implements Command {
    public function __construct(private Light $light) {}
    public function execute(): string { $this->light->on = false; return 'light off'; }
}

final class Invoker {
    private array $queue = [];
    public function add(Command $c): void { $this->queue[] = $c; }
    public function run(): void {
        foreach ($this->queue as $c) { echo $c->execute(), PHP_EOL; }
    }
}

$light = new Light();
$inv = new Invoker();
$inv->add(new TurnOn($light));
$inv->add(new TurnOff($light));
$inv->run();

Command Bus

使い分け

理解度チェック

まとめ