User defined attributes use

[H. S. Teoh]

On Mon, Sep 16, 2013 at 10:38:58PM +0200, Namespace wrote:
> >D is not only about arrays.
> It's a big plus. ;)
> 
> 
> >[1] Obviously, not a practical short term option for the existing D2
> >language.  That's probably clear from the context, and the question
> >was meant to be rhetorical -- but it could actually be done and would
> >make sense; it's just not a change that would make enough of a
> >difference on its own; the cost would be to high.
> 
> Why to high? Too much compiler magic or dmd internal dependences?

I disagree that it's too high. It just needs *somebody* with the right
knowledge about DMD internals (and enough free time on their hands >:-))
to pull it off.

The problem with the current AA implementation is that it's
schizophrenically split across DMD, aaA.d, and object.di. Martin Nowak
recently cleaned it up somewhat (removed the horrible code duplication
between aaA.d and object.di that used to be there) but fundamental
issues remain, a major cause of which is the fact that aaA.d operates on
typeinfo's rather than the direct types (this isn't a problem in and of
itself, but the problem is that *only* AA keys have the benefit of their
typeinfo's being available to AA functions, which means AA *values* that
require non-trivial postblits and other such things are fundamentally
broken in horrible ways).

Moreover, DMD still retains way too much knowledge about AA internals,
so sometimes it gets mapped to struct AssociativeArray, sometimes
directly mapped to aaA.d, and sometimes a buggy inconsistent mixture of
both. And the code that emits these different schizophrenic parts are
sprinkled all over different unrelated parts of DMD, making any cleanup
attempt rather challenging, to say the least. And of course, any
non-correspondence between any of these parts means yet another AA bug
waiting to happen.

Cleaning up this mess once and for all will unquestionably do a world of
good to D.


T

-- 
You are only young once, but you can stay immature indefinitely. -- azephrahel