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# -*-org-*-
# TITLE: 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.