Sergey Gromov wrote:
Wed, 26 Nov 2008 09:12:12 -0600, Andrei Alexandrescu wrote:
Don wrote:
My suspicion is, that if you allowed all signed-unsigned operations when
at least one was a literal, and made everything else illegal, you'd fix
most of the problems. In particular, there'd be a big reduction in
people abusing 'uint' as a primitive range-limited int.
Well, part of my attempt is to transform that abuse into legit use. In
other words, I do want to allow people to consider uint a reasonable
model of natural numbers. It can't be perfect, but I believe we can make
it reasonable.
Notice that the fact that one operand is a literal does not solve all of
the problems I mentioned. There is for example no progress in typing u1
- u2 appropriately.
Although it would be nice to have a type which was range-limited, 'uint'
doesn't do it. Instead, it guarantees the number is between 0 and
int.max*2+1 inclusive. Allowing mixed operations encourages programmers
to focus the benefit of 'the lower bound is zero!' while forgetting that
there is an enormous downside ('I'm saying that this could be larger
than int.max!')
I'm not sure I understand this part. To me, the larger problem is
underflow, e.g. when subtracting two small uints results in a large uint.
I'm totally with Don here. In math, natural numbers are a subset if
integers. But uint is not a subset of int. If it were, most of the
problems would vanish. So it's probably feasible to ban uint from
SafeD, implement natural numbers by some other means, and leave uint for
low-level wizardry.
That's also a possibility - consider unsigned types just "bags of bits"
and disallow most arithmetic for them. They could actually be eliminated
entirely from the core language because they can be implemented as a
library. I'm not sure how that would feel like.
I guess length would return an int in that case?
Andrei
