| Commit message (Collapse) | Author | Age | Files | Lines |
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Reflection API exhibits a tension inherent to experimental things:
on the one hand we want it to grow into a beautiful and robust API,
but on the other hand we have to deal with immaturity of underlying mechanisms
by providing not very pretty solutions to enable important use cases.
In Scala 2.10, which was our first stab at reflection API, we didn't
have a systematic approach to dealing with this tension, sometimes exposing
too much of internals (e.g. Symbol.deSkolemize) and sometimes exposing
too little (e.g. there's still no facility to change owners, to do typing
transformations, etc). This resulted in certain confusion with some internal
APIs living among public ones, scaring the newcomers, and some internal APIs
only available via casting, which requires intimate knowledge of the
compiler and breaks compatibility guarantees.
This led to creation of the `internal` API module for the reflection API,
which provides advanced APIs necessary for macros that push boundaries
of the state of the art, clearly demarcating them from the more or less
straightforward rest and providing compatibility guarantees on par with
the rest of the reflection API.
This commit does break source compatibility with reflection API in 2.10,
but the next commit is going to introduce a strategy of dealing with that.
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Previously, all built-in macros were assumed to be whitebox, but that’s
actually not the case. Just quasiquote macros have to be whitebox, while
the rest can be blackbox.
This also fixes SI-8091, because blackbox macros are typechecked differently
and therefore the necessary implicit conversion kicks in. If `f”...”` were
to remain a whitebox macro, then due to the changes introduced in commit
https://github.com/scala/scala/commit/a3b33419b02cafb7e2c6fed6dd96151859fc7d77
we would have to explicitly ascribe its expansion as String to achieve the same effect.
After I made reify blackbox, several tests had to be changed, because
we now explicitly ascribe the expansion with `c.Expr[T]`, which changes `toString`.
Also, a number of less obvious corrections had to be applied, because
things like `reify(<constant>).splice` have stopped being optimized away
due to `reify(<constant>)` no longer having a narrow `c.Expr[<constant>.type]`,
making it ineligible for constant folding.
Moreover, this change forced me to adjust our approach to positioning
blackbox wrappings, because after being changed to blacbox and starting using
wrappings, f”...” interpolators used in the compiler started crashing
-Yrangepos builds. Now wrapping Typed nodes are assigned with transparent
positions.
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I started out looking to limit the noise from empty type
bounds, i.e. the endless repetition of
class A[T >: _root_.scala.Nothing <: _root_.scala.Any]
This led me to be reminded of all the unnecessary and
in fact damaging overreaches which are performed during parsing.
Why should a type parameter for which no bounds are
specified be immediately encoded with this giant tree:
TypeBounds(
Select(Select(Ident(nme.ROOTPKG), tpnme.scala_), tpnme.Nothing),
Select(Select(Ident(nme.ROOTPKG), tpnme.scala_), tpnme.Any)
)
...which must then be manually recognized as empty type bounds?
Truly, this is madness.
- It deftly eliminates the possibility of recognizing
whether the user wrote "class A[T]" or "class A[T >: Nothing]"
or "class A[T <: Any]" or specified both bounds. The fact
that these work out the same internally does not imply the
information should be exterminated even before parsing completes.
- It burdens everyone who must recognize type bounds trees,
such as this author
- It is far less efficient than the obvious encoding
- It offers literally no advantage whatsoever
Encode empty type bounds as
TypeBounds(EmptyTree, EmptyTree)
What could be simpler.
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The name looks weird in the scaladoc overview panel,
so I decided to do a last-minute rename.
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This brings all the files into line with the .gitattributes
settings, which should henceforth be automatically maintained
by git.
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As the experience has shown, there's no need for a separate layer of reflection
in scala-library.jar. Therefore I'm putting an end to it.
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Instead of trying to serialize the entire universe and failing miserably
(which happens now), exprs and type tags will now serialize their creators
and deserialize into scala.reflect.basis.
Since creators produced by reification are not serializable right now,
serialization will crash. That's a small improvement over state of the art
functionality-wise, but it's a step forward robustness-wise.
Next step in this direction is generation of serialization code for creators.
Related issues: SI-5919 and SI-5908. Also see the discussion at scala-internals
http://groups.google.com/group/scala-internals/browse_thread/thread/ef63f8b5bd194c7c
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Implements SIP 16: Self-cleaning macros: http://bit.ly/wjjXTZ
Features:
* Macro defs
* Reification
* Type tags
* Manifests aliased to type tags
* Extended reflection API
* Several hundred tests
* 1111 changed files
Not yet implemented:
* Reification of refined types
* Expr.value splicing
* Named and default macro expansions
* Intricacies of interaction between macros and implicits
* Emission of debug information for macros (compliant with JSR-45)
Dedicated to Yuri Alekseyevich Gagarin
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