On 11/11/06 9:10 PM, "Sascha Krissler" <boost-dev@k.datenfreihafen.de> wrote:
i had this little idea. when yo want to customize a class with a container like
template <typename T, typename Container> struct Foo;
then you must instanciate it with:
Foo<int, std::vector<int> >
the second int is redundant. [TRUNCATE failed solution with a template-based template parameter and a better solution with MPL reading or writing template parameters]
No, it's not redundant. STL stuff involving containers is set up so a direct, non-template, class can be used as a container. Solutions involving certain template games will break that philosophy. I use asserts to make sure a container is compliant with what I need. Here is an example from some code I'm putting in the Sandbox: //======================================================================== #include <memory> // for std::allocator #include <boost/type_traits/is_same.hpp> // for boost::is_same #include <boost/static_assert.hpp> // for BOOST_STATIC_ASSERT namespace boost { namespace math { //... template < int Radix, class Allocator = ::std::allocator<int> > class big_radix_whole { // Pre-conditions // (SNIP constraints on "Radix") BOOST_STATIC_ASSERT( (is_same<int, typename Allocator::value_type>::value) ); // ... }; //... } } //======================================================================== Now I can use a non-template allocator class like: //======================================================================== #include <cstddef> class my_int_allocator // Note: _no_ "template" preamble! { public: typedef int value_type; typedef std::size_t size_type; typedef std::ptrdiff_t difference_type; typedef int * pointer; typedef int const * const_pointer; typedef int & reference; typedef int const & const_reference; // You're screwed if you need "rebind". // Put address, max_size, allocate, deallocate, etc. here... }; //======================================================================== -- Daryle Walker Mac, Internet, and Video Game Junkie darylew AT hotmail DOT com