LazyOption.php

<?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Component\OptionsResolver;

/**
 * An option that is evaluated lazily using a closure.
 *
 * @author Bernhard Schussek <bschussek@gmail.com>
 */
class LazyOption
{
    /**
     * The underlying closure.
     * @var \Closure
     */
    private $closure;

    /**
     * The previous default value of the option.
     * @var mixed
     */
    private $previousValue;

    /**
     * Creates a new lazy option.
     *
     * @param \Closure $closure    The closure used for initializing the
     *                             option value.
     * @param mixed $previousValue The previous value of the option. This
     *                             value is passed to the closure when it is
     *                             evaluated.
     *
     * @see evaluate()
     */
    public function __construct(\Closure $closure, $previousValue = null)
    {
        $this->closure = $closure;
        $this->previousValue = $previousValue;
    }

    /**
     * Evaluates the underlying closure and returns its result.
     *
     * The given Options instance is passed to the closure as first argument.
     * The previous default value set in the constructor is passed as second
     * argument.
     *
     * @param Options $options The container with all concrete options.
     *
     * @return mixed The result of the closure.
     */
    public function evaluate(Options $options)
    {
        $previousValue = $this->previousValue;
        $closure = $this->closure;

        if ($previousValue instanceof self) {
            $previousValue = $this->previousValue->evaluate($options);
        }

        // Performs a bit better than __invoke() and call_user_func()
        return $closure($options, $previousValue);
    }
}