[Boost-users] [enable_if] How to enable a constructor

Hi all, I am playing around with enable_if and I want to create a constructor switch. The code is the following: ------------------------------------------------ struct NullType{}; struct TestType{}; struct NonNull{}; template struct TemplateStruct { TemplateStruct(int i, typename boost::enable_if, void* >::type dummy = 0) { std::cout << "One Param == " << i << std::endl; } TemplateStruct(int i, int j, typename boost::disable_if, void* >::type dummy = 0) { std::cout << "Two Param == " << i << "," << j << std::endl; } }; int main(int /*argc*/, char**) { TemplateStruct<TestType>(1); TemplateStruct(1,2); return 0; } ------------------------------------- I want that the first Ctor is only available when a NullType is passed in and if not that the second one is available but not the first. I don't want to do a class specialization because the class is rather big and extracting all the methods to a common class would be difficult. So how can I reuse the template parameter U for the Ctors enable_if? Or is this simply not possible? Regards, Michael