Zephir\FunctionCall::isBuiltInFunction PHP Method

    public function isBuiltInFunction($functionName)
    {
        switch ($functionName) {
            case 'memstr':
            case 'get_class_ns':
            case 'get_ns_class':
            case 'camelize':
            case 'uncamelize':
            case 'starts_with':
            case 'ends_with':
            case 'prepare_virtual_path':
            case 'create_instance':
            case 'create_instance_params':
            case 'create_symbol_table':
            case 'globals_get':
            case 'globals_set':
            case 'merge_append':
            case 'get_class_lower':
                return true;
        }
        return false;
    }