Re: [c++, cxx-reflection] Initial thoughts on type reflection.

[Phil Edwards <phil at jaj dot com>]

On Sun, Mar 09, 2003 at 07:42:13PM -0800, Zack Weinberg wrote:
> Phil Edwards <phil at jaj dot com> writes:
> 
> > Gaby and I have been discussing this in private, on and off, for a few weeks.
> > I've made 3 or 4 implementations with varying tradeoffs.  Even though the
> > cxx-reflection-branch is experimental, it would nice to get some public
> > discussion before any code starts getting checked in.
> 
> Is this intended for C as well as C++?  I can certainly see uses -
> <tgmath.h> for instance.

Yes.

> Your magic reflection expressions want to be (extended) integer
> constant expressions, and in particular suitable for use in template
> parameters.  Which I bet you've already thought of, but it does mean
> that there are ABI implications here.

Thought of and implemented.  :-)

I wouldn't mind a subthread forking here and discussing the ABI implications.
These are meant to be removed/collapsed/folded/whatever before code
generation begins.  All reflection work should take place on the host,
none on the target.

For example, the "is it const" code fragment you have below -- which,
incidentally, I already have wrappers for :-) -- becomes

    if (true)

after builtins are expanded.


> >     enum __CVQualifier__
> 
> 1) Calling these "CV" qualifiers is inappropriate: it's an
>    abbreviation for "const or volatile" and now we have restrict too.
>    Suggest you just call them qualifiers and use __qual_ as a prefix.

Good idea.

> 2) These should be bitmasks, so you can write
> 
>    if (__builtin_qualifiers (type) & __qual_const)
>      /* type is const-qualified; don't care about volatile or restrict */

They already are; I left out the enum values because I thought it might be
a distraction, but I should have left them in.  Choices which are mutually
exclusive start at 0 and increase monotonically; ones such as __Qualifier__
and __SpecialFunctions__, for which multiple choices are possible, are
bitmasks for precisely the above usage.


Phil

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