Mapped class to wrapped value types can't work as expected

Elements Elements Bugs
4

This issue is found because I try to make things like:

#if ECHOES
public __mapped struct gint => int {
}
#elif COOPER || NOUGAT
public __mapped class gint => int? {
}
#endif

So I can use gint to implement generic interface/delegate with a clean code:

public interface ITestInterface<T>{
    T get();
}

public class TestClass : ITestInterface<gint>{
    public gint get() => 5;
}

Otherwise, cross-platform code will be terrible:

public class TestClass : ITestInterface<int>{
    #if ECHOES
    public int get() => 5;
    #else
    public int? get() => 5;
    #endif
}

Another example:

public class List<T> {
    public delegate int Comparer<T>(T a, T b);

    public void sort(Comparer<T> comparer) {
        // ...
    }
}

public static class ListComparer {

    // Without gint
    #if ECHOES
    public static int intDescent(int a, int b) {
    #else
    public static int intDescent(int? a, int? b) {
    #endif
        return b - a;
    }


    // With gint
    public static int intDescent(gint a, gint b) {
        return b - a;
    }
}

public class TestCode {
    public void test() {
        var list = new List<int>();
        list.sort(ListComparer.intDescent);
    }
}