Re: RFC, problem with g++4

[Florian Weimer <fw@deneb.enyo.de>]

* Goswin von Brederlow:

> The proper use of this construct seems to be:
>
> template <typename T>
> struct Foo {
>   static const unsigned N = T::N;
>   char bar[N];
> };
>
> struct Bla {
>   static const unsigned N;
> };
>
> const unsigned Bla::N = 10;
>
> int main() {
>   Foo<Bla> foo;
> }

This program is ill-formed.  

Bla::N is not an integral constant expression (5.19/1) and thus does
not make Foo::N an integral constant expression, either (9.4.2/4).

I will file a couple of bug reports.  Some of these things might
actually undocumented G++ extensions.

> Correct me if I'm wrong but doesn't that
>
> 1.) Only move the const declaration from the template into the
> template parameter?
>
> 2.) Cause the template to have static member N in every file that uses
> the template and for every type?
>
> 3.) Cause Bla to have a static member N in every file that uses
> the template and for every type?

I don't understand these questions.

If the definition of Bla::N appears in multiple translation units, the
one definition rule is violated and the program is ill-formed.