DIP30, delegates more destruction for your pleasure

[Maxim Fomin]

On Thursday, 14 March 2013 at 03:12:21 UTC, deadalnix wrote:
>> From " UFCS as delegates": example with function foo(ref uint 
>> a) raises concern about ABI implementation. Currently context 
>> pointer is passed through RDI and arguments are passed 
>> differently. There would be a problem with functions like 
>> foo() which do not know from where to take an argument - are 
>> they called directly or like a closure?
>>
>
> I don't think ABI should be part of D spec. Or should it ?
>
> Anyway, I don't see any reason to have all kind of different 
> ABI for function call, and this is a good opportunity to unify 
> everything using the context as a regular, first argument.

ABI, at least partly, is and should be part of the spec. 
Otherwise it has some of the C++ problems. And the point was not 
about ABI in a sense of adding piece of information to chapter in 
dlang.org, but about implementing compiler. I am not enthusiastic 
about most DIPs presented recently because 1) without Walter and 
Andrei approval 2) without somebody willing to implement it, DIP 
turns to be a paper intellect exercise and corresponding ideas 
defence in the forum.

>> Frankly, I see this simpler: delegate = function pointer + 
>> data pointer, so they should follow language rules (especially 
>> regarding qualifiers).
>>
>
> It is a tempting idea, but do not work. Consider :
>
> void delegate() immutable a;
> const void delegate() b = a;
>
> This would be forbidden as covariance of function parameters 
> and transitivity act in opposite directions.

The problem is that there is 1 qualifier in current syntax and 
two underlying objects.