I have a class that I want to have accept 0-5 arguments in any order for it's constructor. Each argument is a const references to one of 5 possible class types. All arguments must be distinct in type, passing the same type twice in an error. Passing an argument that is not one of the 5 supported types is also an error. How do you go about implementing something like this? I figure first you have to create a constructor for each arity but then how do you constrain the constructors as described above? I imagine it would involve enable_if. class widget { widget(); template< class A > widget( const A& a ); template< class A, class B > widget( const A& a, const B& b ); template< class A, class B, class C > widget( const A& a, const B& b, const C& c ); template< class A, class B, class C, class D > widget( const A& a, const B& b, const C& c, const D& d ); template< class A, class B, class C, class D, class E > widget( const A& a, const B& b, const C& c, const D& d, const E& e ); };