libstdc++ not conforming with --enable-concepts-check?

[Matt Austern]

On Sep 22, 2004, at 8:55 AM, Nathan Myers wrote:

> On Wed, Sep 22, 2004 at 04:35:40PM +0200, Paolo Carlini wrote:
>> magfr@lysator.liu.se wrote:
>>
>>> Hello.
>>>
>>> If I try to compile the attached program and have built the compiler 
>>> with
>>> --enable-concept-checks that fails but as far as I can see from the
>>> standard
>>> queue only requires that the elements should be CopyConstructible, 
>>> there is
>>> no requirement for DefaultConstructability, so I think that is a bug 
>>> in the
>>> concept checking code.
>>
>> Hi and thanks for your message: in my opinion, indeed, we have a bug.
>>
>>      // Matt Austern's book puts DefaultConstructible here, the C++
>>      // standard places it in Container
>
> Maybe std::queue shouldn't require DefaultConstructible, but isn't its
> default container std::deque, and shouldn't deque be enforcing it?
> Why is it failing to do so?

There are two different issues: does the container type have to be 
default constructible (yes: it says so in table 65), and do the 
container elements have to be default constructible (no; 23.1/3 gives 
the requirements on container elements, and "default constructible" 
isn't one of them, and implementations go to a great deal of effort to 
make sure that they don't require it by accident).

If our concept checking code is requiring container elements to be 
default constructible, that's just a bug.  Probably a very simple one.

			--Matt