From: Larry Evans (jcampbell3_at_[hidden])
Date: 2001-06-25 15:31:43
Vesa Karvonen wrote:
>
> Anyway, I'm interested in seeing plausible uses of template template
> parameters. I think that this subject might be more appropriate for a C++
> newsgroup, except that I'm mainly interested in seeing actual use of template
> template parameters in existing libraries.
The smart pointer garbage collection classes in the zip files in:
http://groups.yahoo.com/group/boost/files/GarbageCollectByTmplSpecializa/
use template template parameters. I'd be interested in knowing if they can
be avoided.
>
> ...
>
> At least in template metaprogramming, template template parameters seem to
> have limited use and member templates seem much more powerful. The only truly
> plausible "use" I know of, is that of adapting a metafunction into a
> "metafunction object" (is there a better name for this concept?):
>
> template
> < template<class> class fun
> >
> struct make_fun_obj
> { template
> < class T
> >
> struct code : fun<T>
> {
> };
> };
>
> Metafunction objects, which rely on member templates make it possible to:
> - bind parameters (and curry):
>
> template
> < class fun_obj
> , class p1
> >
> struct bind_2nd
> { template
> < class p0
> >
> struct code : fun_obj::template code<p0,p1>
> {
> };
> };
>
> - return a metafunction object or store it in a type data structure.
>
> These techniques are quite powerful. For instance, I'm using lists that
This technique was also used in the subjprox_vec and subjprox_one templates
in GarbageCollectByTmplSpecializa to enable the smart pointer analog to
vector of vectors and pointers to pointers.