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From mariogarcia <>
Subject [GitHub] groovy pull request #439: WIP Add groovy-macro docs
Date Sun, 09 Oct 2016 14:47:10 GMT
Github user mariogarcia commented on a diff in the pull request:
    --- Diff: src/spec/doc/core-metaprogramming.adoc ---
    @@ -2829,6 +2829,153 @@ to use the Groovy Console, in particular the AST browser tool,
to gain knowledge
     resource for learning is the[AST
     test suite.
    +==== Macros
    +===== Introduction
    +Until version 2.5.0, when developing AST transformations, developers should have a deep
knowledge about how the AST
    +(Abstract source tree) was built by the compiler in order to know how to add new expressions
or statements during
    +compile time.
    +Although the use of `org.codehaus.groovy.ast.tool.GeneralUtils` static methods could
mitigate the burden of creating
    +expressions and statements, it's still a low-level way of writing those AST nodes directly.
    +We needed something to abstract us from writing the AST directly and that's exactly what
Groovy macros were made for.
    +They allow you to add code during compile time directly, without having translate the
code you had in mind to the
    +`org.codehaus.groovy.ast.*` node related classes.
    +===== Statements and expressions
    +Lets see an example, lets create a local AST transformation. `@AddMessageMethod`. When
applied to a given class it
    +will add a new method called `getMessage` to that class. The method will return "42".
The annotation it's pretty
    +straight forward:
    +How would look like the AST transformation without the use of a macro:
    +<1> Create a return statement
    +<2> Create a constant expression "42"
    +<3> Adding the code to the new method
    +<4> Adding the new method to the annotated class
    +If you're not used to the AST API, that definitely doesn't look like the code you had
in mind. Now look how the
    +previous code looks like with the use of macros.
    --- End diff --

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