module blah;

alias BS = BSA;

alias BS = BSB;

​

template BSA(alias T)

{

}

​

template BSB(T)

{

}

​

void foo()

{

    void bar(alias composite)()

    {

        foreach (member; __traits(allMembers, composite))

            enum a = __traits(compiles, __traits(getMember, composite, member));

    }

​

    bar!blah;

}