On Wednesday, 19 November 2014 at 17:55:26 UTC, Andrei
Alexandrescu wrote:
On 11/19/14 6:04 AM, Don wrote:
Almost everybody seems to think that unsigned means positive.
It does not.
That's an exaggeration. With only a bit of care one can use D's
unsigned types for positive numbers. Please let's not reduce
the matter to black and white.
Andrei
Even in the responses in this thread indicate that about half of
the people here don't understand unsigned.
"unsigned" means "I want to use modulo 2^^n arithmetic". It does
not mean, "this is an integer which cannot be negative".
Using modulo 2^^n arithmetic is *weird*. If you are using
uint/ulong to represent a non-negative integer, you are using the
incorrect type.
"With only a bit of care one can use D's unsigned types for
positive numbers."
I do not believe that that statement to be true. I believe that
bugs caused by unsigned calculations are subtle and require an
extraordinary level of diligence. I showed an example at DConf,
that I had found in production code.
It's particularly challenging in D because of the widespread use
of 'auto':
auto x = foo();
auto y = bar();
auto z = baz();
if (x - y > z) { ... }
This might be a bug, if one of these functions returns an
unsigned type. Good luck finding that. Note that if all
functions return unsigned, there isn't even any signed-unsigned
mismatch.
I believe the correct statement, is "With only a bit of care one
can use D's unsigned types for positive numbers and believe that
one's code is correct, even though it contains subtle bugs."
