| Twig Internals |
| ============== |
| |
| Twig is very extensible and you can hack it. Keep in mind that you |
| should probably try to create an extension before hacking the core, as most |
| features and enhancements can be handled with extensions. This chapter is also |
| useful for people who want to understand how Twig works under the hood. |
| |
| How does Twig work? |
| ------------------- |
| |
| The rendering of a Twig template can be summarized into four key steps: |
| |
| * **Load** the template: If the template is already compiled, load it and go |
| to the *evaluation* step, otherwise: |
| |
| * First, the **lexer** tokenizes the template source code into small pieces |
| for easier processing; |
| |
| * Then, the **parser** converts the token stream into a meaningful tree |
| of nodes (the Abstract Syntax Tree); |
| |
| * Finally, the *compiler* transforms the AST into PHP code. |
| |
| * **Evaluate** the template: It means calling the ``display()`` |
| method of the compiled template and passing it the context. |
| |
| The Lexer |
| --------- |
| |
| The lexer tokenizes a template source code into a token stream (each token is |
| an instance of ``\Twig\Token``, and the stream is an instance of |
| ``\Twig\TokenStream``). The default lexer recognizes 13 different token types: |
| |
| * ``\Twig\Token::BLOCK_START_TYPE``, ``\Twig\Token::BLOCK_END_TYPE``: Delimiters for blocks (``{% %}``) |
| * ``\Twig\Token::VAR_START_TYPE``, ``\Twig\Token::VAR_END_TYPE``: Delimiters for variables (``{{ }}``) |
| * ``\Twig\Token::TEXT_TYPE``: A text outside an expression; |
| * ``\Twig\Token::NAME_TYPE``: A name in an expression; |
| * ``\Twig\Token::NUMBER_TYPE``: A number in an expression; |
| * ``\Twig\Token::STRING_TYPE``: A string in an expression; |
| * ``\Twig\Token::OPERATOR_TYPE``: An operator; |
| * ``\Twig\Token::PUNCTUATION_TYPE``: A punctuation sign; |
| * ``\Twig\Token::INTERPOLATION_START_TYPE``, ``\Twig\Token::INTERPOLATION_END_TYPE``: Delimiters for string interpolation; |
| * ``\Twig\Token::EOF_TYPE``: Ends of template. |
| |
| You can manually convert a source code into a token stream by calling the |
| ``tokenize()`` method of an environment:: |
| |
| $stream = $twig->tokenize(new \Twig\Source($source, $identifier)); |
| |
| As the stream has a ``__toString()`` method, you can have a textual |
| representation of it by echoing the object:: |
| |
| echo $stream."\n"; |
| |
| Here is the output for the ``Hello {{ name }}`` template: |
| |
| .. code-block:: text |
| |
| TEXT_TYPE(Hello ) |
| VAR_START_TYPE() |
| NAME_TYPE(name) |
| VAR_END_TYPE() |
| EOF_TYPE() |
| |
| .. note:: |
| |
| The default lexer (``\Twig\Lexer``) can be changed by calling |
| the ``setLexer()`` method:: |
| |
| $twig->setLexer($lexer); |
| |
| The Parser |
| ---------- |
| |
| The parser converts the token stream into an AST (Abstract Syntax Tree), or a |
| node tree (an instance of ``\Twig\Node\ModuleNode``). The core extension defines |
| the basic nodes like: ``for``, ``if``, ... and the expression nodes. |
| |
| You can manually convert a token stream into a node tree by calling the |
| ``parse()`` method of an environment:: |
| |
| $nodes = $twig->parse($stream); |
| |
| Echoing the node object gives you a nice representation of the tree:: |
| |
| echo $nodes."\n"; |
| |
| Here is the output for the ``Hello {{ name }}`` template: |
| |
| .. code-block:: text |
| |
| \Twig\Node\ModuleNode( |
| \Twig\Node\TextNode(Hello ) |
| \Twig\Node\PrintNode( |
| \Twig\Node\Expression\NameExpression(name) |
| ) |
| ) |
| |
| .. note:: |
| |
| The default parser (``\Twig\TokenParser\AbstractTokenParser``) can be changed by calling the |
| ``setParser()`` method:: |
| |
| $twig->setParser($parser); |
| |
| The Compiler |
| ------------ |
| |
| The last step is done by the compiler. It takes a node tree as an input and |
| generates PHP code usable for runtime execution of the template. |
| |
| You can manually compile a node tree to PHP code with the ``compile()`` method |
| of an environment:: |
| |
| $php = $twig->compile($nodes); |
| |
| The generated template for a ``Hello {{ name }}`` template reads as follows |
| (the actual output can differ depending on the version of Twig you are |
| using):: |
| |
| /* Hello {{ name }} */ |
| class __TwigTemplate_1121b6f109fe93ebe8c6e22e3712bceb extends Template |
| { |
| protected function doDisplay(array $context, array $blocks = []) |
| { |
| // line 1 |
| echo "Hello "; |
| echo twig_escape_filter($this->env, (isset($context["name"]) ? $context["name"] : null), "html", null, true); |
| } |
| |
| // some more code |
| } |
| |
| .. note:: |
| |
| The default compiler (``\Twig\Compiler``) can be changed by calling the |
| ``setCompiler()`` method:: |
| |
| $twig->setCompiler($compiler); |