@@ -5,3 +5,46 @@ title: Architecture
55partof :reflection
66num :6
77---
8+
9+ ===TreeCreator===
10+ A mirror-aware factory for trees.
11+
12+ In the reflection API, artifacts are specific to universes and
13+ symbolic references used in artifacts (e.g.` scala.Int ` ) are resolved by mirrors.
14+
15+ Therefore to build a tree one needs to know a universe that the tree is going to be bound to
16+ and a mirror that is going to resolve symbolic references (e.g. to determine that` scala.Int `
17+ points to a core class` Int ` from scala-library.jar).
18+
19+ ` TreeCreator ` implements this notion by providing a standalone tree factory.
20+
21+ This is immediately useful for reification. When the compiler reifies an expression,
22+ the end result needs to make sense in any mirror. That's because the compiler knows
23+ the universe it's reifying an expression into (specified by the target of the` reify ` call),
24+ but it cannot know in advance the mirror to instantiate the result in (e.g. on JVM
25+ it doesn't know what classloader use to resolve symbolic names in the reifee).
26+
27+ Due to a typechecker restriction (no eta-expansion for dependent method types),
28+ ` TreeCreator ` can't have a functional type, so it's implemented as class with an apply method.
29+
30+ ===TypeCreator===
31+ A mirror-aware factory for types.
32+
33+ In the reflection API, artifacts are specific to universes and
34+ symbolic references used in artifacts (e.g.` scala.Int ` ) are resolved by mirrors.
35+
36+ Therefore to build a type one needs to know a universe that the type is going to be bound to
37+ and a mirror that is going to resolve symbolic references (e.g. to determine that` scala.Int `
38+ points to a core class` Int ` from scala-library.jar).
39+
40+ ` TypeCreator ` implements this notion by providing a standalone type factory.
41+
42+ This is immediately useful for type tags. When the compiler creates a type tag,
43+ the end result needs to make sense in any mirror. That's because the compiler knows
44+ the universe it's creating a type tag for (since` TypeTag ` is path-dependent on a universe),
45+ but it cannot know in advance the mirror to instantiate the result in (e.g. on JVM
46+ it doesn't know what classloader use to resolve symbolic names in the type tag).
47+
48+ Due to a typechecker restriction (no eta-expansion for dependent method types),
49+ ` TypeCreator ` can't have a functional type, so it's implemented as class with an apply method.
50+