如何使用 scala 宏生成顶级 class/object
How to generate top-level class/object with scala macro
我们知道，在某些方法中使用 scala 宏很容易创建内部 class。
但我想知道是否可以生成顶级class/object？
如果答案是肯定的，那么如何避免生成相同的 class 两次？
我的 scala 版本是 2.11
- Top-level expansions must retain the number of annottees, their flavors and their names, with the only exception that a class might expand into a same-named class plus a same-named module, in which case they automatically become companions as per previous rule.
https://docs.scala-lang.org/overviews/macros/annotations.html
所以你转换顶级
@annot
class A
进入
class A
object A
或
@annot
object A
进入
class A
object A
也有 c.introduceTopLevel 但已被删除。
Context.introduceTopLevel. The Context.introduceTopLevel API, which used to be available in early milestone builds of Scala 2.11.0 as a stepping stone towards type macros, was removed from the final release, because type macros were rejected for including in Scala and discontinued in macro paradise.
https://docs.scala-lang.org/overviews/macros/changelog211.html
Scala Macro: Define Top Level Object
introduceTopLevel has provided a long-requested functionality of generating definitions that can be used outside macro expansions. However, metaprogrammers have
quickly discovered that introduceTopLevel is dangerous. Top-level scope is a resource shared between the typechecker and user metaprograms, so mutating it with
introduceTopLevel can lead to compilation order problems. For example, if one file
in a compilation run relies on definitions created by a macro expansion performed in
another file, compiling the former before the latter may lead to unexpected compilation
errors.
https://infoscience.epfl.ch/record/226166/files/EPFL_TH7159.pdf（第 5.2.3 节结论）
如果您要生成的随播广告已经存在，那么您在宏注释 macroTransform 中 return 的随播广告将替换原来的随播广告。你不需要注意会有两个 "companions"，编译器会注意的。但如果是这种情况，通常情况下你肯定会匹配（无论只有注释者还是注释者 + 同伴）。
我们知道，在某些方法中使用 scala 宏很容易创建内部 class。 但我想知道是否可以生成顶级class/object？ 如果答案是肯定的，那么如何避免生成相同的 class 两次？ 我的 scala 版本是 2.11
- Top-level expansions must retain the number of annottees, their flavors and their names, with the only exception that a class might expand into a same-named class plus a same-named module, in which case they automatically become companions as per previous rule.
https://docs.scala-lang.org/overviews/macros/annotations.html
所以你
@annot
class A
进入
class A
object A
或
@annot
object A
进入
class A
object A
也有 c.introduceTopLevel 但已被删除。
Context.introduceTopLevel. TheContext.introduceTopLevelAPI, which used to be available in early milestone builds of Scala 2.11.0 as a stepping stone towards type macros, was removed from the final release, because type macros were rejected for including in Scala and discontinued in macro paradise.
https://docs.scala-lang.org/overviews/macros/changelog211.html
Scala Macro: Define Top Level Object
introduceTopLevelhas provided a long-requested functionality of generating definitions that can be used outside macro expansions. However, metaprogrammers have quickly discovered thatintroduceTopLevelis dangerous. Top-level scope is a resource shared between the typechecker and user metaprograms, so mutating it withintroduceTopLevelcan lead to compilation order problems. For example, if one file in a compilation run relies on definitions created by a macro expansion performed in another file, compiling the former before the latter may lead to unexpected compilation errors.
https://infoscience.epfl.ch/record/226166/files/EPFL_TH7159.pdf（第 5.2.3 节结论）
如果您要生成的随播广告已经存在，那么您在宏注释 macroTransform 中 return 的随播广告将替换原来的随播广告。你不需要注意会有两个 "companions"，编译器会注意的。但如果是这种情况，通常情况下你肯定会匹配（无论只有注释者还是注释者 + 同伴）。