[phobos] Design question - is return type Algebraic?

[Shin Fujishiro]

My Any implementation used auto ref for return types.  But it turned
out to be too restrictive for Algebraic.  Consider this:
----------
Algebraic!(int, BigInt) x;
auto y = ++x;
// Error: mismatched function return type inference of BigInt and int
----------

Maybe operator overloads should return Algebraic!(int, BigInt).  Then,
should we do the same for opDispatch() for unity?
----------
Algebraic!(R1, R2, ...) opDispatch(string method, Args...)(Args args)
{
    final switch (_which) {
        case A: return Algebraic( objA.method(args) );
        case B: return Algebraic( objB.method(args) );
        ...
    }
}
----------

I'm a bit reluctant to do so.  Returning Algebraic disables return-by-
ref facility.  Furthermore, we can't do the following if a result is
packed in an Algebraic:
----------
void fun(R)(R r) if (isSomeChar!(ElementType!R))
{
}
Algebraic!(string, CharReader) r;
r = "abc";
fun(r);     // Error!  ElementType is Algebraic!(dchar)
----------
Too bad, Algebraic r is not a 'duck' anymore.

I'm stucked.  Do you have any ideas?


Shin