C++汎用プログラミング学習std::conditional

eg:
std::conditional //   true，      
std::conditional::type   T
std::conditional//   false，      
std::conditional::type   U

eg:
int j = 10
std::conditional100), int, 
    std::conditional80), float, 
         std::conditional60), char, double>::type
    >::type
>::type var;

std::cout<