C++泛型编程学习 std::conditional

eg:
std::conditional<true, T, U> //第一个true， 那个么  
std::conditional<true, T, U>::type  为T
std::conditional<true, T, U>//第一个false， 那个么  
std::conditional<true, T, U>::type  为U

eg:
int j = 10
std::conditional<(j>100), int, 
    std::conditional<(j>80), float, 
         std::conditional<(j>60), char, double>::type
    >::type
>::type var;

std::cout<<typeid(decltype(var)).name()<<std::endl;