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GNU ease.js Traits
==================
The trait implementation is not yet complete; this is the list of known
issues/TODOs. If you discover any problems, please send an e-mail to
bug-easejs@gnu.org.
Aside from the issues below, traits are stable and ready to be used in
production. See the test cases and performance tests for more information
and a plethora of examples until the documentation is complete.
TODO: Trait Extending
---------------------
Currently, the only way for a trait to override methods of a class it is
being mixed into is to implement a common interface. Traits should
alternatively be able to "extend" classes, which will have effects similar
to Scala in that the trait can only be mixed into that class. Further,
traits should be able to extend and mix in other traits (though such should
be done conservatively).
TODO: Documentation
-------------------
Due to the trait implementation taking longer than expected to complete, and
the importance of the first GNU release, trait documentation is not yet
complete. Instead, traits have been released as a development preview, with
the test cases and performance tests serving as interim documentation.
Comprehensive documentation, including implementation details and rationale,
will be available shortly.
TODO: Static members
--------------------
Static members are currently unsupported. There is no particular difficulty
in implementing them---the author didn't want it to hold up an initial
release (the first GNU release) even further.
TODO: Getters/setters
---------------------
Getters and setters, although they act like properties, should be treated as
though they are methods. Further, they do not suffer from the same
complications as properties, because they are only available in an ES5
environment (as an ECMAScript language feature).
TODO: Mixin Caching
-------------------
The pattern Type.use(...)(...)---that is, mix a trait into a class and
immediate instantiate the result---is a common idiom that can often be
better for self-documentation than storing the resulting class in another
variable before instantiation. Currently, it's also a terrible thing to do
in any sort of loop, as it re-mixes each and every time.
We should introduce a caching system to avoid that cost and make it fairly
cheap to use such an idiom. Further, this would permit the Scala-like
ability to use Type.use in Class.isA checks.
TODO: Public/Protected Property Support
---------------------------------------
Private properties are currently supported on traits because they do not
affect the API of the type they are mixed into. However, due to limitations
of pre-ES5 environments, implementing public and protected member epoxying
becomes ugly in the event of a fallback, amounting essentially to
re-assignment before/after trait method proxying. It is possible, though.
This is not a necessary, or recommended, feature---one should aim to
encapsulate all data, not expose it---but it does have its legitimate uses.
As such, this is not a high-priority item.
TODO: Trait-specific error messages
-----------------------------------
All error messages resulting from traits should refer to the trait by name
and any problem members by name, and should offer context-specific
suggestions for resolution. Currently, the errors may be more general and
may reflect the internal construction of traits, which will be rather
confusing to users.
TODO: Performance enhancements
------------------------------
The current trait implementation works well, but is relatively slow
(compared to how performant it could be). While this is sufficient for most
users' uses, there is plenty of room for improvement. Until that time, be
mindful of the performance test cases in the `test/perf' directory.
TODO: Intermediate object as class
----------------------------------
The immediate syntax---Foo.use(T)()---is a short-hand equivalent of
Foo.use(T).extend({})(). As such, for consistency, Class.isA should consider
the intermediate object returned by a call to `use' to be a class.
If we are to do so, though, we must make sure that the entire class API is
supported.