traitを使ってObserverパターンを実装してみる

Observable.php

<?php
trait Observable
{
    protected $observers = [];

    /**
     * Adds an observer to this object.
     * @param callable $observer
     * @return Observable
     */
    public function addObserver(callable $observer)
    {
        $this->observers[] = $observer;
        return $this;
    }

    /**
     * If this object has changed, then notify all of the observers.
     */
    protected function _notifyObservers()
    {
        foreach ( $this->observers as $observer )
        {
            call_user_func($observer, $this);
        }
    }
}

ためしに、エラー発生時に通知する仕組みをObserverでやるとこんな感じ。
Observerとしてロガーを渡すと幸せ。

ErrorHandler.php

<?php
class ErrorHandler
{
    use Observable;

    /**
     * Register error handler.
     * @return ErrorHandler
     */
    public function register()
    {
        set_error_handler([$this, 'handleError'], E_ALL);
        return $this;
    }

    /**
     * Handle an error.
     * @param int $severity
     * @param string $message
     * @param string $file
     * @param int $line
     * @return void
     */
    public function handleError($severity, $message, $file, $line)
    {
        if ( ( $severity & error_reporting() ) != $severity )
        {
            return;
        }

        $this->_notifyObservers($severity, $message, $file, $line);
    }

    /**
     * If this object has changed, then notify all of the observers.
     * @param int $severity
     * @param string $message
     * @param string $file
     * @param int $line
     * @return Observable
     */
    protected function _notifyObservers($severity, $message, $file, $line)
    {
        foreach ( $this->observers as $observer )
        {
            call_user_func($observer, $this);
        }
    }

<?php

$logger = function($severity, $message, $file, $line){
    echo sprintf("%sの%u行目で、「%s」っていうエラーがレベル%uで発生したみたいだよ！", $file, $line, $message, $severity), PHP_EOL;
};

$errorHandler = new ErrorHandler();
$errorHandler->addObserver($logger)->register();