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 {}
I think this only happens to work by accident, because compilers tend to defer instantiation of function templates until the end of the translation unit, when a proper instantiation of Base is available. But without a compiler that doesn't I don't think I can come up with code that shows this. In any case, this makes *my* head hurt, and that's saying something. Sebastian