Gabriel Dos Reis <dosreis@cmla.ens-cachan.fr> wrote in message news:<fl8zjmfm3h.fsf@sel.cmla.ens-cachan.fr>...
> kavdeiv@mail.ru (Kiril Avdeiv) writes:
>
> | Can anyone explain how detecting the extra template parameters through
> | template template parameters work.
>
>
>    template<template<typename> class Container>
>    void foo() { /* ... */ }
>
>    #include <valarray>
>
>    int main()
>    {
>       foo<std::valarray>();
>    }
>
> This won't work if there is an additional parameter (even hidden) for
> std::valarray -- yes, I know there is out there a broken compiler
> which doesn't mind about template template argument signture matching.

Thank you Gabriel!

Kiril

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I posted this one to comp.lang.c++.moderated but no one was able to
answer. Given that it's LWG's library issue list that made me write
that post, I hope to find an answer here...

On this new group I got to hear that the reason why extra template
parameters for the standard library classes are prohibited (even if
default template arguments are given) is because "it seems added
template parameters can be detected by a program using
template-template parameters".

Can anyone explain how detecting the extra template parameters through
template template parameters work.

Thank you
Kiril.

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kavdeiv@mail.ru (Kiril Avdeiv) writes:

| Can anyone explain how detecting the extra template parameters through
| template template parameters work.


   template<template<typename> class Container>
   void foo() { /* ... */ }

   #include <valarray>

   int main()
   {
      foo<std::valarray>();
   }

This won't work if there is an additional parameter (even hidden) for
std::valarray -- yes, I know there is out there a broken compiler
which doesn't mind about template template argument signture matching.

--
Gabriel Dos Reis, dosreis@cmla.ens-cachan.fr

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