Boost logo

Boost :

Subject: Re: [boost] Provisional Boost.Generic and Boost.Auto_Function (concepts without concepts)
From: Dean Michael Berris (mikhailberis_at_[hidden])
Date: 2010-12-14 06:34:02

On Tue, Dec 14, 2010 at 6:14 PM, Dave Abrahams <dave_at_[hidden]> wrote:
> At Tue, 14 Dec 2010 15:35:04 +0800,
> Dean Michael Berris wrote:
>> I don't see an obvious problem here in terms of ODR here because you
>> are using a template -- which by definition still gets instantiated
>> anyway across multiple translation units,
> No, not by definition.  EDG still has a link-time instantiation
> option.

Ah, I haven't had much experience with EDG and link-time template
instantiation. Interesting, I haven't looked for that in other

>> and is not required to have a single definition anyway.
> That would be news to me!  Do you have a reference?

Actually, I was referring to having the template have a single
definition per translation unit. However, as you've pointed out, EDG
has a link-time instantiation option for templates, which is also
standards compliant behavior.

> That said, if all the type difference occurs *within* the decltype
> *and* within the decltype there are no ODR violations, I *think* there
> is technically no ODR violation.  But I suggest asking a real
> hard-core core-language expert on this one if you care about technical
> correctness.

That was what I was thinking too -- because Matt's relying on the
decltype being the "discriminant" or the thing that differentiates it
from other instantiations of the template, then it wouldn't
technically be an ODR violation. I have to get my hands on the latest
draft standard to see whether the ODR rules have changed for C++0x.

Maybe those writing the compilers (and those involved in the standard
committee and this section that are also in this list) can chime in
and correct all of my mis-interpretations. ;)

>> The only worrying thing is that if the nested function invocation
>> referred to has a static but non-extern linkage, and thus will be
>> defined in multiple translation units -- some compilers issue a
>> diagnostic on this occurrence although I forget if the standard
>> requires that a diagnostic be emitted in cases where you have nested
>> static functions in templates. Maybe those who actually know enough
>> about the relevant sections of the standard can chime in.
> If someone prepares a _minimal_ representative example of the question, I'll
> be happy to run it by someone who knows for you.

Let me see if I can come up with a simple C++03 example to illustrate
what I meant above. :)

Dean Michael Berris

Boost list run by bdawes at, gregod at, cpdaniel at, john at