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Diffstat (limited to 'src/library/scala/reflect/base/TreeCreator.scala')
| -rw-r--r-- | src/library/scala/reflect/base/TreeCreator.scala | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/src/library/scala/reflect/base/TreeCreator.scala b/src/library/scala/reflect/base/TreeCreator.scala index c9c8de2307..5de0094f1f 100644 --- a/src/library/scala/reflect/base/TreeCreator.scala +++ b/src/library/scala/reflect/base/TreeCreator.scala @@ -1,6 +1,26 @@ package scala.reflect package base +/** A mirror-aware factory for trees. + * + * In the reflection API, artifacts are specific to universes and + * symbolic references used in artifacts (e.g. `scala.Int`) are resolved by mirrors. + * + * Therefore to build a tree one needs to know a universe that the tree is going to be bound to + * and a mirror that is going to resolve symbolic references (e.g. to determine that `scala.Int` + * points to a core class `Int` from scala-library.jar). + * + * `TreeCreator` implements this notion by providing a standalone tree factory. + * + * This is immediately useful for reification. When the compiler reifies an expression, + * the end result needs to make sense in any mirror. That's because the compiler knows + * the universe it's reifying an expression into (specified by the target of the `reify` call), + * but it cannot know in advance the mirror to instantiate the result in (e.g. on JVM + * it doesn't know what classloader use to resolve symbolic names in the reifee). + * + * Due to a typechecker restriction (no eta-expansion for dependent method types), + * `TreeCreator` can't have a functional type, so it's implemented as class with an apply method. + */ abstract class TreeCreator { def apply[U <: Universe with Singleton](m: MirrorOf[U]): U # Tree } |