車輪を再発明

gistfile1.php

<?php

class Optional {
    private $obj;

    public function __construct ($obj) { $this->obj = $obj; }

    private function _ocheck () {
        return is_object($this->obj);
    }

    private function _fcheck ($func) {
        return $this->_ocheck() && method_exists($this->obj, $func);
    }

    private function _pcheck ($prop) {
        return $this->_ocheck() && property_exists($this->obj, $prop);
    }

    public function __call ($func, $arguments) {
        if (!$this->_fcheck($func)) { return new Optional(null); }
        return new Optional(call_user_func_array(array($this->obj, $func), $arguments));
    }

    public function __invoke () {
        if (!$this->_fcheck('__invoke')) { return new Optional(null); }
        return new Optional(call_user_func_array($this->obj, (array)func_get_args()));
    }

    public function __set ($name, $value) {
        if (!$this->_pcheck($name)) { return new Optional(null); }
        $this->obj->$name = $value;
        return $this;
    }

    public function __get ($name) {
        if (!$this->_pcheck($name)) { return new Optional(null); }
        return new Optional($this->obj->$name);
    }

    public function __isset ($name) {
        if (!$this->_pcheck($name)) { return false; }
        return isset($this->obj->$name);
    }

    public function __unset ($name) {
        if (!$this->_pcheck($name)) { return; }
        unset($this->obj->$name);
    }

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

    /**
     * map :: Optional o => o a -> (a -> b) -> o b
     * @param callable $callable :: a -> b
     */
    public function map ($callable = null) {
        if (!is_callable($callable)) { return new Optional(null); }
        return new Optional($callable($this->obj));
    }

    /**
     * flatMap :: Optional o => o a -> (a -> o b) -> o b
     * @param callable $callable :: Optional o => a -> o b
     */
    public function flatMap ($callable = null) {
        if (!is_callable($callable)) { return new Optional(null); }
        $result = $callable($this->obj);
        if (!is_object($result) || !is_a($result, 'Optional')) { return new Optional($result); }
        return $result;
    }
}