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Re: Template alias destructor call

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On 22.01.2020 16:01, Paavo Helde wrote:
> Please consider:
> 
> #include <new>
> 
> template <typename T, typename U>
> class A {};
> 
> template <typename T>
> using B = A<T, int>;
> 
> template <typename T>
> void foo(B<T>* x) {
>      x->~B<T>();  // this line failing with clang
> }
> 
> int main() {
>      alignas(sizeof(B<int>)) char buff[sizeof(B<int>)];
>      B<int>* p = new (buff) B<int>;
>      foo(p);
> }
> 
> gcc and msvc compile this just fine. However, clang refuses:
> 
> test1.cpp:11:6: error: no member named 'B' in 'A<int, int>'
>          x->~B<T>();
>              ^
> test1.cpp:17:2: note: in instantiation of function template 
> specialization 'foo<int>' requested here
>          foo(p);
>          ^
> 1 error generated.
> 
> Who is right? And if clang, then how to write an explicit B<T> 
> destructor call without relying on how B<T> happens to be defined?

C++17 §10.1.7.2/1 defines the /type-name/ after `~` as one of

   class-name
   enum-name
   typedef-name
   simple-template-id

This suggests that no matter how /simple-template-id/ turns out a fix 
can be to use a /typedef-name/.

§17.2/1 defines /simple-template-id/ as (transcribed to typewriter-ish)

   template-name `<` template-argument-list OPTIONAL `>`

The question is then whether your template alias `B` is a 
/template-name/. The very same paragraph defines /template-name/ 
syntactically as

    identifier

It then explains (in a non-normative note plus in normative text in 
paragraph 3) that it's the name lookup that determines if a name is a 
/template-name/. I fail to find that. However, §17.5.7 states that

      An alias template is a name for a family of types. The name of the 
alias template is a /template-name/.

So this is a bug in dang.

Workaround probably as mentioned above.

- Alf

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Template alias destructor call Paavo Helde <myfirstname@osa.pri.ee> - 2020-01-22 17:01 +0200
  Re: Template alias destructor call "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2020-01-23 11:26 +0100
    Re: Template alias destructor call Paavo Helde <myfirstname@osa.pri.ee> - 2020-01-23 13:09 +0200
      Re: Template alias destructor call Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-01-27 01:40 -0800

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