ジェネリックラムダ２つを受け取りどちらか１つを返す関数型言語のif式っぽいの

Generic_lambda_If.hpp

//sample http://txt-txt.hateblo.jp/entry/2014/01/21/180633
#include<boost\variant\variant.hpp>
#include<type_traits>
#include<utility>


template<class F1,class F2>
class BiGenLambda
{
	template<class F>
	using Result_of = typename std::result_of<F>::type;
	template<class ...Args>
	using Check_result_of_is_same=typename std::enable_if<
			std::is_same<
				Result_of<F1(Args...)>, Result_of<F2(Args...)>
			>::value
		>::type;
public:
	BiGenLambda(const F1&f)
		:data_(f)
	{}
	BiGenLambda(const F2&f)
		:data_(f)
	{}
	template<class F,class Result_Type>
	struct Visitor
	{
		F f_;
		using result_type = Result_Type;
		Visitor(const F&f)
			:f_(f)
		{}
		template <class T>
		result_type operator()(T& x)const
		{
			return f_(x);
		}
		template <class T>
		result_type operator()(const T& x)const
		{
			return f_(x);
		}
	};

	template<class ...Args, class = Check_result_of_is_same<Args...>>
	auto operator()(Args&&...args)
		->Result_of<F1(Args...)>
	{
		auto vi = [&args...](auto c){return c(args...); };
		using Vi = decltype(vi);
		return boost::apply_visitor(Visitor<Vi, Result_of<F1(Args...)>>(vi), data_);
	}
private:
	boost::variant<F1, F2> data_;
};



template<class Than,class Else>
BiGenLambda<Than, Else>  If(bool r, Than&&than_, Else&&else_)
{
	if (r)return than_;
	else return else_;
}