Re: [boost] Re: is_convertible corner case

From: David Abrahams (dave_at_[hidden])
Date: 2003-01-24 20:32:47

"Paul Mensonides" <pmenso57_at_[hidden]> writes:

> ----- Original Message -----
> From: "David Abrahams" <dave_at_[hidden]>
>
>> I tend to agree on a "moral/aesthetic" level, but on a practical level
>> we have to tread carefully.  The question, "can we just have an
>> operator which produces a compile-time constant value saying whether
>> its operand is a valid expression?" has come up a few times in the
>> committee.  Each time, the implementors looked at their codebases and
>> said "oooh, that's really hard to do."  I think the short form of the
>> reason is that C++ compilers generally don't have the ability to
>> recover from errors reliably.  That may explain why your 2nd, 3rd,
>> 4th... diagnostic messages tend to be useless gibberish ;-)
>>
>> So, I'd like to push for something like that but practically speaking
>> I'm not sure how to get there.
>
> The problems are not insurmountable though (with an "is_valid_expression").
> You aren't dealing with entire language at this point, only an
> expression.

And which parts of the language does that fail to drag in?  Not many.

Actually, not that it matters, but I think I'm misquoting the original
request, which was, IIRC, "tell us whether evaluating this expression
should produce a compilation error."  Howard knows for sure...

-- 
                       David Abrahams
   dave_at_[hidden] * http://www.boost-consulting.com
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