Creates `reflectors`, as a meta-meta feature that enables dynamic selection of a "mirror system".

test_reflectable/test/meta_reflectors_test.dart

+// Copyright (c) 2015, the Dart Team. All rights reserved. Use of this
+// source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+// File being transformed by the reflectable transformer.
+// Creates a `MetaReflector` which may be used to reflect on the set of
+// reflectors themselves.
+//
+// Independence: This is the only library in this program where both the
+// reflector classes and the domain classes are seen together. The program
+// as a whole illustrates a number of ways in which it is possible to make
+// reflection, usage of reflection, and application specific classes (here
+// known as 'domain classes') independent of each other, statically and
+// dynamically.
+
+library test_reflectable.test.meta_reflectors_test;
+
+@GlobalQuantifyCapability(r"\.(M1|M2|M3|A|B|C|D)$", const Reflector())
+@GlobalQuantifyCapability(r"\.(M1|M2|M3|B|C|D)$", const Reflector2())
+@GlobalQuantifyCapability(r"\.(C|D)$", const ReflectorUpwardsClosed())
+@GlobalQuantifyCapability(r"\.(C|D)$", const ReflectorUpwardsClosedToA())
+@GlobalQuantifyCapability(r"\.(C|D)$", const ReflectorUpwardsClosedUntilA())
+import "package:reflectable/reflectable.dart";
+import "meta_reflectors_domain_definer.dart";
+import "meta_reflectors_definer.dart";
+import "meta_reflectors_scoping.dart";
+import "meta_reflectors_user.dart";
+
+Map<String, Iterable<Reflectable>> scopeMap = <String, Iterable<Reflectable>>{

[sigurdm, 2015/10/09 07:52:04]

While this is a perfectly valid approach, I still think this mapping could be
more elegantly defined by having the scopes represented as Reflectors. 
Then adding a reflector to a scope would amount to annotating it with the
scope-reflector (perhaps via GlobalQuantifyCapability).

Each of the scope-reflectors is then annotated by scope-meta-reflector and the
mapping can be constructed as:

```
Map<Reflectable, Iterable<Reflectable>> scopeMap = {};
scopeMetaReflector.annotatedClasses.forEach(
    (ClassMirror scopeReflectorMirror) {
  Reflectable scopeReflector =
      Reflectable.getInstance(scopeReflectorMirror);
  scopeMap[scopeReflector] = 
      scopeReflector.annotatedClasses.map(Reflectable.getInstance);
});
```

Then any package can add reflectors to any scope that it knows about, and the
mapping is automatically updated. (in your case the mapping needs to be in the
end-users control, otherwise it cannot be updated).

[eernst, 2015/10/09 10:09:05]

Why don't you write that as an extra test case? ;)

[sigurdm, 2015/10/09 10:47:20]

Good idea!

+  "polymer": <Reflectable>[const Reflector(), const ReflectorUpwardsClosed()],
+  "observe": <Reflectable>[const Reflector2(), const ReflectorUpwardsClosed()]
+};
+
+@ScopeMetaReflector()
+Iterable<Reflectable> reflectablesOfScope(String scope) => scopeMap[scope];
+
+main() {
+  doit();
+}