Re: Finding out whether a class instantiates a template

Date	2012-03-22 22:30 -0400
From	Ed Anson <EdAnson@comcast.net>
Newsgroups	comp.lang.c++
Subject	Re: Finding out whether a class instantiates a template
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On 3/22/12 10:49 AM, cartec69@gmail.com wrote:
> On Thursday, March 1, 2012 6:10:48 PM UTC-6, Ed Anson wrote:
>> My problem involves template parameters (of class templates) -- not
>> function parameters. What I have looks something like this:
>>
>> template<class T>  class foo {};
>> template<class U>  class bar {};
>>
>> where T is required to be an instantiation of bar<U>, such as
>>
>> bar<foo<int>  >  A;
>>
>
> I'm assuming you mean "U is required to be an instantiation of foo<>" since that's what your example is. I think it's standard practice to use a "trait" template for this:
>
> template<typename T>  struct is_foo { static const bool value = false; };
> template<typename T>  struct is_foo<  foo<T>  >  { static const bool value = true; };
>
> So T is an instation of foo iff is_foo<T>::value == true.

Yes. And yes! Thank you. Of course it's obvious, now that you show it to me.

/Ed

Thread

Finding out whether a class instantiates a template Ed Anson <EdAnson@comcast.net> - 2012-02-29 19:50 -0500
  Re: Finding out whether a class instantiates a template Christian Gollwitzer <auriocus@gmx.de> - 2012-03-01 07:58 +0100
    Re: Finding out whether a class instantiates a template Ed Anson <EdAnson@comcast.net> - 2012-03-01 19:10 -0500
      Re: Finding out whether a class instantiates a template cartec69@gmail.com - 2012-03-22 07:49 -0700
        Re: Finding out whether a class instantiates a template Ed Anson <EdAnson@comcast.net> - 2012-03-22 22:30 -0400
          Re: Finding out whether a class instantiates a template Ed Anson <EdAnson@comcast.net> - 2012-03-23 18:31 -0400
            Re: Finding out whether a class instantiates a template Marc <marc.glisse@gmail.com> - 2012-03-24 23:08 +0000

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