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moved lifter and h2db typemacro examples to separate repos #142

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Dec 25, 2012
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moved lifter and h2db typemacro examples to separate repos #142

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4 changes: 2 additions & 2 deletions overviews/macros/typemacros.md
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Expand Up @@ -26,7 +26,7 @@ Just as def macros make the compiler execute custom functions when it sees invoc
Db.Coffees.update(brazilian.copy(price = 10))
println(Db.Coffees.all)

The full source code of the `H2Db` type macro is provided [at Github](https://github.com/scalamacros/kepler/tree/paradise/macros/test/files/run/macro-typemacros-fourth-proto), and this guide covers its most important aspects. First the macro generates the statically typed database wrapper by connecting to a database at compile-time (tree generation is explained in [the reflection overview](http://docs.scala-lang.org/overviews/reflection/overview.html)). Then it uses the <span class="label success">NEW</span> `c.introduceTopLevel` API to insert the generated wrapper into the list of top-level definitions maintained by the compiler. Finally, the macro returns an `Apply` node, which represents a super constructor call to the generated class. <span class="label warning">NOTE</span> that type macros are supposed to expand into `c.Tree`, unlike def macros, which expand into `c.Expr[T]`. That's because `Expr`s represent terms, while type macros expand into types.
The full source code of the `H2Db` type macro is provided [at Github](https://github.com/xeno-by/typemacros-h2db), and this guide covers its most important aspects. First the macro generates the statically typed database wrapper by connecting to a database at compile-time (tree generation is explained in [the reflection overview](http://docs.scala-lang.org/overviews/reflection/overview.html)). Then it uses the <span class="label success">NEW</span> `c.introduceTopLevel` API to insert the generated wrapper into the list of top-level definitions maintained by the compiler. Finally, the macro returns an `Apply` node, which represents a super constructor call to the generated class. <span class="label warning">NOTE</span> that type macros are supposed to expand into `c.Tree`, unlike def macros, which expand into `c.Expr[T]`. That's because `Expr`s represent terms, while type macros expand into types.

type H2Db(url: String) = macro impl

Expand All @@ -41,7 +41,7 @@ The full source code of the `H2Db` type macro is provided [at Github](https://gi
object Db extends H2Db("coffees")
// equivalent to: object Db extends Db$1("coffees")

Instead of generating a synthetic class and expanding into a reference to it, a type macro can transform its host instead by returning a `Template` tree. Inside scalac both class and object definitions are internally represented as thin wrappers over `Template` trees, so by expanding into a template, type macro has a possibility to rewrite the entire body of the affected class or object. You can see a full-fledged example of this technique in the talk linked above.
Instead of generating a synthetic class and expanding into a reference to it, a type macro can transform its host instead by returning a `Template` tree. Inside scalac both class and object definitions are internally represented as thin wrappers over `Template` trees, so by expanding into a template, type macro has a possibility to rewrite the entire body of the affected class or object. You can see a full-fledged example of this technique [at Github](https://github.com/xeno-by/typemacros-lifter).

type H2Db(url: String) = macro impl

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