On 24/08/2012 19:50, pavel wrote:
hi all i post this in the hope someone finds this technique useful
to make long story short, here is a snippet:
template<typename t> //tag deducing util struct base_tag { typedef decltype(get_tag((t*)42)) type; };
template<typename type, typename tag = typename base_tag<type>::type> struct Base //crtp base class { friend tag get_tag(type*); //helper declaration, never defined };
template<typename type> //no mention of tag void f(const Base<type>&) //tag is deduced automatically {}
struct Foo : Base<Foo, void> //derived type {};
int main() { Foo foo; f(foo); }
What's the advantage over template<class T> struct tag_of; template<class Derived> struct Base { typedef typename tag_of<Derived>::type tag; }; struct Foo : Base<Foo> { }; template<> struct tag_of<Foo> { typedef void type; };