Cake\Routing\Route\Route::_writeRoute PHP Method

    protected function _writeRoute()
    {
        if (empty($this->template) || $this->template === '/') {
            $this->_compiledRoute = '#^/*$#';
            $this->keys = [];
            return;
        }
        $route = $this->template;
        $names = $routeParams = [];
        $parsed = preg_quote($this->template, '#');
        preg_match_all('/:([a-z0-9-_]+(?<![-_]))/i', $route, $namedElements);
        foreach ($namedElements[1] as $i => $name) {
            $search = '\\' . $namedElements[0][$i];
            if (isset($this->options[$name])) {
                $option = null;
                if ($name !== 'plugin' && array_key_exists($name, $this->defaults)) {
                    $option = '?';
                }
                $slashParam = '/\\' . $namedElements[0][$i];
                if (strpos($parsed, $slashParam) !== false) {
                    $routeParams[$slashParam] = '(?:/(?P<' . $name . '>' . $this->options[$name] . ')' . $option . ')' . $option;
                } else {
                    $routeParams[$search] = '(?:(?P<' . $name . '>' . $this->options[$name] . ')' . $option . ')' . $option;
                }
            } else {
                $routeParams[$search] = '(?:(?P<' . $name . '>[^/]+))';
            }
            $names[] = $name;
        }
        if (preg_match('#\\/\\*\\*$#', $route)) {
            $parsed = preg_replace('#/\\\\\\*\\\\\\*$#', '(?:/(?P<_trailing_>.*))?', $parsed);
            $this->_greedy = true;
        }
        if (preg_match('#\\/\\*$#', $route)) {
            $parsed = preg_replace('#/\\\\\\*$#', '(?:/(?P<_args_>.*))?', $parsed);
            $this->_greedy = true;
        }
        $mode = '';
        if (!empty($this->options['multibytePattern'])) {
            $mode = 'u';
        }
        krsort($routeParams);
        $parsed = str_replace(array_keys($routeParams), array_values($routeParams), $parsed);
        $this->_compiledRoute = '#^' . $parsed . '[/]*$#' . $mode;
        $this->keys = $names;
        // Remove defaults that are also keys. They can cause match failures
        foreach ($this->keys as $key) {
            unset($this->defaults[$key]);
        }
        $keys = $this->keys;
        sort($keys);
        $this->keys = array_reverse($keys);
    }