Okay, we all [hopefully] know what a discriminated union is, and those
of us who are trying out D2 can probably generally agree that
std.variant.Algebraic makes life a good deal easier in this arena. The
actual usage is different, but it is definitely a gift from heaven.
Except there's one thing it can't do: recursive types.
// D1
struct MyVar {
// ...
union {
int i;
double f;
char[] s;
MyVar[] l; // lists good to go
MyVar[MyVar] h; // hashtables good to go
}
// ...
}
// D2
alias Algebraic!(int, double, string, MyVar[], MyVar[MyVar]) MyVar;
Bzzzzzt! Big ole error!
Fooey. Because I want this, badly (its absolutely necessary for a
program I'm working on). I asked Andrei if he had any suggestion,
especially since it is a known limitation mentioned explicitly in the
specs. No luck. He did have an idea on syntax:
Algebraic!(int, double, string, This[])
Where the 'This' token is recognized specially as recursive. It reads
well, although my first thought was '_' similar to the way std.bind
works. The million dollar question is: how to make this work?
-- Chris Nicholson-Sauls
PS: Apologies, as I just got home from a very long day, so the brain is
a bit tired and I probably came off silly.
