Re: [boost] [static_if] Is there interest in a `static if` emulation library?

Subject: Re: [boost] [static_if] Is there interest in a `static if` emulation library?
From: Robert Ramey (ramey_at_[hidden])
Date: 2014-09-03 12:39:33

Kyle Lutz wrote
> On Tue, Sep 2, 2014 at 10:19 PM, Robert Ramey <

> ramey@

> > wrote:
> 
>> It's been pointed out that the unused branch needs to be compiled even if
>> the result is to be thrown away so that the program won't contain invalid
>> code which will only create a surprise when another type for T is used.
>> Actually, I'm quite sympathetic to this argument.  Generic code shouldn't
>> resolve to invalid code for some types. That mean that it's not really
>> generic.
> 
> Despite your expectations, this is not how optimizers work (or are
> allowed to work). Would you expect the following to compile?
> 
> int main()
> {
>     if(1 == 2){
>         !@#$%^&*();
>     }
>     return 0;
> }

No - I think that's what I said above.

Your example here doesn't depend upon any template parameter so I don't
think it has a lot do with the discussion.  In practice the compile will
trap with an error and the programmer will eliminate the offending code and
that will be the end of it.  If the compiler just through it away, that
would be the end of it as well.  No real difference.  Except that in this
case its very clear that the programmer has some sort of intention which he
hasn't been able to express - so compiling the obviously incorrect code will
tell he hasn't thought enough about what he wants or he made a typographical
mistake.

So far I haven't seen anyone propose an example which benefits from the
original proposal.   Seems to me a solution to a non-existent problem.

Robert Ramey

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