How can I use an alias thats defined in a header file, in the return type (signature) of a function in the .cpp file?

  alias, c++, signature, using, using-declaration

I have a class, Foo, where a using declaration is declared in the header file, e.g. using myInt = int;

If I declare a function in the .cpp file:

myInt Foo::doSomething(){ // myInt is not in recognized here
   myInt x = 5; // myInt is ok here, because its inside Foo namespace

How can I make the myInt valid in the function signature?

Source: Windows Questions C++