Re: template template parameters not working with STL containers

From:

SG <s.gesemann@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Thu, 19 Feb 2009 01:13:51 CST

Message-ID:

<68c649ab-9154-4057-ab9a-f00a00c4d69a@p20g2000yqi.googlegroups.com>

On 18 Feb., 14:26, vl106 <vl...@hotmail.com> wrote:

template <typename T,
template <typename> class CONT = std::deque>

[...]

error C3201: the template parameter list for class template
'std::deque' does not match the template parameter list for template
parameter 'CONT'

This is because std::deque is a class template that takes more than
one template parameter "typename T". It also takes an allocator
"class Alloc".

For reasons I'm not aware of the C++ standard says that you can't pass
such a class template -- even with a default allocator type -- as a
template template parameter that only takes one template parameter.

This is probably one reason why template template parameters are not
so popular. In future C++ you will be able to do a "template typedef"

   template<typename T>
   using vector_with_standard_alloc = std::vector<T>;

so you can use "vector_with_standard_alloc" as default template
argument. Another workaround is to define your own container class
template with only one template parameter (like MyVector).

Cheers!
SG

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