Option.php

<?php

abstract class COption
{
    public static function of($data)
    {
        return ($data != NULL ? new CSome($data) : new CNone());
    }

    public abstract function isDefined();

    public abstract function map($mapping);

    public abstract function flatMap($mapping);

    public abstract function filter($filter);

    public abstract function __invoke($action);

    public abstract function get();

    public abstract function getOrElse($default);
};

final class CSome extends COption
{
    private $data = NULL;

    protected function __construct($data)
    {
        $this->data = $data;
    }

    public function isDefined()
    {
        return true;
    }

    public function map($mapping)
    {
        return new CSome($mapping($this->data));
    }

    public function flatMap($mapping)
    {
        return $mapping($this->data);
    }

    public function filter($filter)
    {
        return ($filter($this->data) == true ? $this : COption::of(NULL));
    }

    public function __invoke($action)
    {
        $action($this->data);
    }

    public function get()
    {
        return $this->data;
    }

    public function getOrElse($default)
    {
        return $this->data;
    }
};

final class CNone extends COption
{
    protected function __construct()
    {
    }

    public function isDefined()
    {
        return false;
    }

    public function map($mapping)
    {
        return $this;
    }

    public function flatMap($mapping)
    {
        return $this;
    }

    public function filter($filter)
    {
        return $this;
    }

    public function __invoke($action)
    {
    }

    public function get()
    {
        throw false;
    }

    public function getOrElse($default)
    {
        return $default;
    }
};