On Wednesday, 3 April 2013 at 14:54:03 UTC, Steven Schveighoffer
wrote:
On Wed, 03 Apr 2013 07:33:05 -0400, Don
<turnyourkidsintoc...@nospam.com> wrote:
Yeah, but I think that what this is, is demonstrating what a
useful concept a positive integer type is. There's huge value
in statically knowing that the sign bit is never negative.
Unfortunately, using uint for this purpose gives the wrong
semantics, and introduces these signed/unsigned issues, which
are basically silly.
Personally I suspect there aren't many uses for unsigned types
of sizes other than the full machine word. In all the other
sizes, a positive integer would be more useful.
Hm.. would it be useful to have a "guaranteed non-negative"
integer type? Like array length. Then the compiler could make
that assumption, and do something like what I did as an
optimization?
Subtracting from that type would result in a plain-old int.
-Steve
I think it would be extremely useful. I think "always positive"
is a fundamental mathematical property that isn't captured by the
type system. But I fear the heritage from C just has too much
momentum.
One thing we could do immediately, without changing anything in
the language definition at all, is add range propagation for
array length.
So that, for any array A, A.length is in the range 0 ..
(size_t.max/A[0].sizeof)
which would mean that unless A is of type byte, ubyte, void, or
char, the length is known to be a positive integer. And of course
for a static array, the exact length is known.
Although that has very limited applicability (only works within a
single expression), I think it might help quite a lot.
