Generic code: @autoconst, @autopure, @autonothrow

[Pillsy]

Andrei Alexandrescu Wrote:

> On 08/28/2010 08:29 PM, dsimcha wrote:

> > An issue that comes up very frequently when trying to use 
> > const, pure or nothrow in generic code is lack of knowledge 
> > of whether the functions you're calling are 
> > const/pure/nothrow.  For example:

> > T abs(T num) pure nothrow {
> >      return (num<  0) ? -1 * num : num;
> > }
[...]
> > A solution I propose is to allow the annotations @autoconst,
> > @autopure and @autonothrow for template functions.
[...]
> > Does this sound like it could feasibly be implemented and
> > would work well?

> Yah, with the growing interest in applying qualifiers at a larger scale 
> (and making Phobos a good example of such) this is quite timely. 
> I've been mulling myself over a similar proposal.

> What I had in mind is a bit more structured - it would allow 
> selecting a type or an expression and assessing its 
> constness/purity. That would be done just like .sizeof and 
> .stringof work - by defining two more special members
> .constof, .pureof, .nothrowof. For example:

> T abs(T num) (-1 * num).pureof (-1 * num).nothrowof {
>      return (num < 0) ? -1 * num : num;
> }

Could something along the lines of a .qualof member work, for those 
times where you want to duplicate all relevant qualifiers? That seems 
likely to be the general case, and could considerably reduce the 
verbosity involved. 

    T abs(T num) (-1 * num).qualof {
      return (num < 0) ? -1 * num : num;
    }

is even shorter, and would have the possibility of also handling concerns of constness and sharedness and the like properly. 

Cheers,
Pillsy