c++ - What's the difference between using-style and typedef-style?

using IntegerType1 = int;
typedef int IntegerType2;


int main()
{
    IntegerType1 n1 = 1; // OK
    IntegerType2 n2 = 2; // OK
}

My questions are:

1. What's the difference between using-style and typedef-style?




2. As we already have typedef-style, what's the motivation to make using-style become a C++ standard?

Answer

The "using-style" was introduced to allow templated typedefs:

template< typename T >
using int_map = std::map< int, T >;

You can not do this with typedef. I found it strange myself that it was decided to use using and not typedef as the keyword for this, but I guess the committee must have found some problem with extending the typedef syntax.