C++ guys hate static_if?

[Artur Skawina]

On 03/09/13 05:34, H. S. Teoh wrote:
> On Fri, Mar 08, 2013 at 07:50:26PM -0800, Walter Bright wrote:
>> On 3/8/2013 5:19 PM, Brad Anderson wrote:
>>> On Saturday, 9 March 2013 at 00:48:59 UTC, DypthroposTheImposter wrote:
>>>>      Are they full of it? Has it caused the problems they mention
>>>> in
>>>> D?
>>>
>>> Well, the two guys with an alternative proposal (concepts-lite) seem
>>> to hate static if (along with a third guy).
>>>
>>> There seems to be a lot of strawman arguments in this paper.
>>
>> Many of the criticisms in the paper are addressed by our positive
>> experience with static if in D.
> 
> I didn't read the paper, but I have to say that static if in D has been
> extremely, extremely useful in my code. Now that I've become acquianted
> with it, I can't live without it. It's pretty much a necessity when
> writing heavily-templated code. But given C++'s broken template design,
> I can see why its value may not have been appreciated by some people.
> 
> D may still have its warts, but in terms of being a "better C++", I
> think it has done a superb job, especially in the area of templates and
> compile-time mechanisms. Static if + CTFE + sane template syntax =
> readable template code = total win for D over C++.


Let me quote a paragraph from that paper:
> Being a new and realtively simple-to-use new feature, static_if would un-
> doubtedly be used by many who have no need for the relatively small increme-
> natal improvement in performance offered. The library writers for which such
> techniques really are important, already have to tools and skills needed.

No skilled Real Programmer would ever use a language feature that was simple
to use.

Seriously though, they point out several problems, some of which are C++
context specific (like mixing CPP w/ static-if and lack of introspection).
Other mentioned issues are not real problems in practice, or not even
problems at all.

What's left is:
 - static-if not creating scopes /is/ confusing, but what would be a better
   alternative?
 - (static-)if in templates or as template constraints - 
    a) prevents pre-instantiation verification - true, applies to D, but
         not really a big problem, assuming sane application of static-if,
    b) make constraint-based overloading ugly and fragile - true, something
         better is needed for D too. But until that exists, careful use
         of constraints mostly works.

artur