using type alias such as using A = int(int)

With type alias we could introduce new type alias for example

using A = int(*)(int);

is similar to

typedef int(*A)(int);

I find the following code is also legal for current C++ compiler

using A = int(int);

I was wondering what's the type of A and how to use it ( I did not find it useful myself)

Here's the code, it works in gcc 6.3 and clang 4.0

#include <iostream>
#include <functional>
#include <typeinfo>
#include <cxxabi.h>
using namespace std;
using A = int(int);
using B = int(*)(int);

int main(){
    int status;
    cout<<sizeof(A)<<endl; //Error in clang 4.0
    cout<<sizeof(B)<<endl;
    cout<<sizeof(function<int(int)>)<<endl;
    cout<<typeid(A).name()<<endl;
    cout<<typeid(B).name()<<endl;
    cout<<typeid(function<int(int)>).name()<<endl;
    cout<<abi::__cxa_demangle(typeid(A).name(), 0, 0, &status)<<endl;
    cout<<abi::__cxa_demangle(typeid(B).name(), 0, 0, &status)<<endl;
    cout<<abi::__cxa_demangle(typeid(function<int(int)>).name(), 0, 0, &status)<<endl;
    return 0;
}

The output is

1
4
16
FiiE
PFiiE
St8functionIFiiEE
int (int)
int (*)(int)
std::function<int (int)>