"Peter Dimov" <[EMAIL PROTECTED]> writes:
> From: "David Abrahams" <[EMAIL PROTECTED]>
>> "Paul Mensonides" <[EMAIL PROTECTED]> writes:
>>
>> > I do, however, agree that we need more support from the language for
>> > generic programming and some type of standardized API into the
>> > compiler's type system. And I definitely think that "undefined
>> > behavior" is unreasonable when the situation is easily diagnosable
>> > and not platform specific.
>>
>> 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 ;-)
>
> But how does this apply to is_convertible<X, int> when a private X::operator
> int()? Or are you discussing something else?
See below.
> I see no reason to make that undefined behavior. It's either "false", "true"
> (Comeau says true BTW), "unspecified", or "ill formed, no diagnostic
> required" - in order of preference.
"Ill formed with diagnostic required" was the possibility I was
thinking of.
You're right; undefined behavior is certainly not in the picture for
this case.
Never mind my brainless interjection, please ;-)
--
David Abrahams
[EMAIL PROTECTED] * http://www.boost-consulting.com
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