RE: template template parameters (was Re: [boost] Re: Special fun ctions, octonions, quaternions in the CVS)

From: Aleksey Gurtovoy (alexy_at_[hidden])
Date: 2001-06-26 10:45:19

 Jeremy Siek wrote:
> Sure. The template template parameter workaround allows more 
> flexibility in the template types that are used as parameters. For 
> example, suppose the template parameter is a container:
> 
> #include <vector>
> 
> template <template <class U> class C>
> struct foo {
>   struct bar { };
>   C<bar> c;
> };
> 
> int main()
> {
>   foo<std::vector> f;
>   return 0;
> }
> 
> 
> Now, what if we don't want to use the default allocator of 
> std::vector, but some other allocator? How can we pass in std::vector into

> foo but also specify some other allocator? With template templates 
> parameters you can not do this. 

Actually, with template template parameters you cannot even do the above ;),

Comeau C/C++ 4.2.44 (Sep 30 2000 11:56:08) for _MS_WINDOWS_x86_BETA3

"E:\depot\libs\template_params.cpp", line 12: error #999: class template
          "std::vector" is not compatible with template template parameter
"C"
    foo<std::vector> f;
        ^