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Re: Allow use of constants and types from not-instantiation-ed template

From: William Linkmeyer <wlink10_at_[hidden]>
Date: Mon, 20 Dec 2021 14:18:34 -0500
Maybe introducing friendlier syntax for instantiating templates would work. Something like a “templating” block, similar to how the “using” block works with namespaces.

i.e.:

templating<class SomeClass> {
auto variable = Foo::bar;
}

Which would resolve as

auto variable = Foo<SomeClass>::bar;

WL

> On Dec 20, 2021, at 1:09 PM, Hani Deek via Std-Proposals <std-proposals_at_[hidden]> wrote:
>
> 
> >
> > Hello,
> >
> > So, let's just allow use of a types and static constants from
> > not-instantiation-ed template class (if possible):
> >
> > template<typename T>
> > struct Foo{
> > constexpr static int bar = 0x01;
> > };
> > int i = Foo::bar; // Doesn't compile now, but could
> > int j = Foo<class Nonexisting>::bar; // Ugly hack but works
> >
>
> I think the proposal should be to allow a namespace to have the same name as a class template.
>
> For example,
>
> ---------------------------------
> namespace Foo
> {
> constexpr int bar = 0x01;
> }
>
> template<typename T>
> struct Foo
> {
> static constexpr T bar = 0x02;
> };
>
> int i = Foo::bar; //Foo is a namespace name
> int j = Foo<short>::bar; //Foo is a class template name
> ---------------------------------
>
> In order for this proposal to work, we will need to add new rules to the name lookup rules. We will need to define contexts in which a name is assumed to be a namespace name rather than a template name, and other contexts for the opposite assumption. We will also need a disambiguation mechanism for contexts where both a namespace name and a template name may be used.
>
> Adding those new name lookup rules will be a radical change to C++, and I think that many people will oppose the proposal on the grounds that the benefits are not worth the hassle.
> --
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Received on 2021-12-20 13:18:38