Forward declarations of template specilizations.

[Bill Baxter]

On Sun, Nov 16, 2008 at 5:14 PM, Christian Kamm
<kamm-incasoftware at removethis.de> wrote:
>> I have an interesting issue, that makes me curious on how D handles it.
>>
>> (Traits template code)
>
> You cannot spread out template specializations across modules. If you define
>
> template Trait(T : S); in a.d and
> template Trait(T : C); in b.d and try to use
> alias Trait!(S) sinst; in use.d, you'll get
> Error: a.Trait(T : S) at a.d(3) conflicts with b.Trait(T : C) at b.d(3)
>
> because the two Traits live in separate scopes. This makes C++ style trait
> templates just not work in D.
>
> Does anyone know an equivalent?

I think what Ryan said there is the general approach you have to take.
Don't specialize the traits template, but rather pass in a whole new
template as an alias parameter to the main template.

This would be a good thing to add here:
http://www.prowiki.org/wiki4d/wiki.cgi?PortingFromCxx
Is there some canonical example of where you use specialized traits
templates in C++?  Or is this maybe a more general issue, like porting
ADL code in C++.

Not traits templates, but another ADL example is how you see IO done
often in C++.  With overloads for some common function like
"write(Stream& o, ModuleSpecificType& val)".  This pattern doesn't
translate directly to D either.  Suggestions?

--bb