Proposal: user defined attributes

[Steven Schveighoffer]

On Fri, 16 Mar 2012 14:33:37 -0400, Adam D. Ruppe  
<destructionator at gmail.com> wrote:

> On Friday, 16 March 2012 at 18:07:18 UTC, Steven Schveighoffer wrote:
>> Quote from TDPL (section 5.9.1 on page 156):
>
> Huh. There's nothing I can see in the compiler that even
> hints at this. The @ thing is just another storage class
> as far as it's concerned right now.

Right, the user-defined portion is not implemented.

>
>> Nor do I see a huge number of library or user-defined ones springing up.
>
> Yeah.
>
> I still really like my expression idea though, but
> thinking about your strategy, we could say:
>
> When you see @, if it is a compiler word after it,
> parse it that way. Otherwise, try to get a function
> call out of it.

The way I'd like to see it work (and not being a compiler writer, I have  
no idea if/how this would work) is:

When you see @, call a CTFE function with that name.

The compiler defines intrinsic functions @property, @disable, etc.  which  
return intrinsic data types that get appended to the attribute list.  Then  
the compiler recognizes those data types in the attribute list when  
deciding how things should be compiled.

This might not be feasible given the current implementation, or how  
compilers are designed, I have no idea.

> The return value is appended to the declaration's
> attribute expression list (so the end result is the same
> as I was thinking.)

Yes.  And I'd like to see the other intrinsic attributes appended (and  
queryable) as well.

What we also may need in the @annotation declaration is an alias of the  
thing being compiled (again, don't know how feasible this is)

for example:

@annotation property(alias sym)() { static assert(is(sym == function));  
return INTRINSIC.isProperty;}

Maybe that's going too far :)

-Steve