C++ typedef for partial templates
i need to do a typedef like this.
template< class A, class B, class C >
class X
{
};
template< class B, class C >
typedef X< std::vector<B>, B, C > Y;
I just found that it is not supported in C++. Can someone advise me on how to achie开发者_高级运维ve the same through alternative means?
Thanks, Gokul.
If you have a C++0x/C++1x compiler, that will be allowed with a slightly different syntax (it seems as if compilers don't still support this feature):
template <typename B, typename C>
using Y = X< std::vector<B>, B, C >;
You can use other techniques, like defining an enclosed type in a templated struct (like Pieter suggests), or abusing inheritance (avoid if possible):
template <typename B, typename C>
class Y : public X< std::vector<B>, B, C > {};
By placing it in a struct. This idea is called template alias and is part of the C++0x standard (the proposal). But a work-around is given by:
template<class B, class C>
struct Y {
typedef X<std::vector<B>, B, C> type;
};
and use Y<B, C>::type
as your desired type.
And you might be inclined to think gcc4.5 or VS2010 might already support it, as is the case with a big subset of C++0x, but I have to disappoint you, it is as we speak still unsupported :).
精彩评论