C++20 brought us a modules, and while compilers support of this language feature is weak, some already provide at least partial support. 

VS2019 claim that has experimental support of modules. But how make it works?

From microft's docs [Overview of modules in C++](https://docs.microsoft.com/en-us/cpp/cpp/modules-cpp?view=vs-2019) I know that I need file with .ixx extension, let's call it Foo.ixx:
  
    export module Foo;
    
    namespace Foo
    {
       export int f() 
       {
          return 42;
       }
    }
    
 and test.cpp:

    import Foo;
    import std.core;
    
    int main()
    {
        std::cout << "The result of f() is " << Foo::f() << '\n';
    }

How can I build this example from Visual Studio 2019 Developer Command Prompt?