/**
     * Internal method used by compile(). Get PHP code from a closure of function as string.
     *
     * @param object $closure Closure object
     *
     * @return string
     * @expect 'function($a) {return;}' when input function ($a) {return;}
     * @expect 'function($a) {return;}' when input    function ($a) {return;}
     * @expect '' when input 'Directory::close'
     */
    protected static function getPHPCode($closure) {
        if (is_string($closure) && preg_match('/(.+)::(.+)/', $closure, $matched)) {
            $ref = new ReflectionMethod($matched[1], $matched[2]);
        } else {
            $ref = new ReflectionFunction($closure);
        }
        $fname = $ref->getFileName();

        // This never happened, only for Unit testing.
        if (!is_file($fname)) {
            return '';
        }

        $lines = file_get_contents($fname);
        $file = new SplFileObject($fname);
        $file->seek($ref->getStartLine() - 2);
        $spos = $file->ftell();
        $file->seek($ref->getEndLine() - 1);
        $epos = $file->ftell();

        return preg_replace('/^.*?function\s.*?\\((.+?)\\}[,\\s]*;?$/s', 'function($1}', substr($lines, $spos, $epos - $spos));
    }