Twig Internals ¶

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:

  テンプレートをロードします: テンプレートが既にコンパイルされている場合は、それをロードして評価ステップに進みます。それ以外の場合:
  • First, the lexer tokenizes the template source code into small pieces for easier processing;
    まず、レクサーはテンプレートのソース コードをトークン化し、処理を容易にするために小さな断片にします。
  • Then, the parser converts the token stream into a meaningful tree of nodes (the Abstract Syntax Tree);
    次に、パーサーはトークン ストリームを意味のあるノードのツリー (抽象構文ツリー) に変換します。
  • Finally, the compiler transforms the AST into PHP code.
    最後に、コンパイラは AST を PHP コードに変換します。
• Evaluate the template: It means calling the display() method of the compiled template and passing it the context.
  テンプレートを評価する: コンパイルされたテンプレートの display() メソッドを呼び出し、それにコンテキストを渡すことを意味します。

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::BLOCK_START_TYPE、\Twig\Token::BLOCK_END_TYPE: ブロックの区切り文字 ({% %})
• \Twig\Token::VAR_START_TYPE, \Twig\Token::VAR_END_TYPE: Delimiters for variables ({{ }})
  \Twig\Token::VAR_START_TYPE、\Twig\Token::VAR_END_TYPE: 変数の区切り文字 ({{ }})
• \Twig\Token::TEXT_TYPE: A text outside an expression;
  \Twig\Token::TEXT_TYPE: 式の外側のテキスト。
• \Twig\Token::NAME_TYPE: A name in an expression;
  \Twig\Token::NAME_TYPE: 式の中の名前。
• \Twig\Token::NUMBER_TYPE: A number in an expression;
  \Twig\Token::NUMBER_TYPE: 式の中の数値。
• \Twig\Token::STRING_TYPE: A string in an expression;
  \Twig\Token::STRING_TYPE: 式の文字列。
• \Twig\Token::OPERATOR_TYPE: An operator;
  \Twig\Token::OPERATOR_TYPE: 演算子。
• \Twig\Token::PUNCTUATION_TYPE: A punctuation sign;
  \Twig\Token::PUNCTUATION_TYPE: 句読点;
• \Twig\Token::INTERPOLATION_START_TYPE, \Twig\Token::INTERPOLATION_END_TYPE: Delimiters for string interpolation;
  \Twig\Token::INTERPOLATION_START_TYPE、\Twig\Token::INTERPOLATION_END_TYPE: 文字列補間の区切り文字。
• \Twig\Token::EOF_TYPE: Ends of template.
  \Twig\Token::EOF_TYPE: テンプレートの終わり。

You can manually convert a source code into a token stream by calling the tokenize() method of an environment:

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$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:

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echo $stream."\n";

Here is the output for the Hello {{ name }} template:

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TEXT_TYPE(Hello )
VAR_START_TYPE()
NAME_TYPE(name)
VAR_END_TYPE()
EOF_TYPE()

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$twig->setLexer($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:

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$nodes = $twig->parse($stream);

Echoing the node object gives you a nice representation of the tree:

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echo $nodes."\n";

Here is the output for the Hello {{ name }} template:

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\Twig\Node\ModuleNode(
  \Twig\Node\TextNode(Hello )
  \Twig\Node\PrintNode(
    \Twig\Node\Expression\NameExpression(name)
  )
)

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$twig->setParser($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:

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$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):

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/* 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
}

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$twig->setCompiler($compiler);