Don, do you have an idea of a simple change to the language that would
prevent at least the most pernicious of these issues?
Andrei
Don Clugston wrote:
The problem is that this code passes:
void main()
{
float x = 0;
x += 2u - 5u;
assert(x == uint.max - 3);
}
But it's pretty unexpected and unhelpful behaviour.
It *doesn't* pass if you set: x = x + 2u - 5u. But x += y is
equivalent to: x = x + cast(typeof(x))y; and since there's an
explicit cast, no error message is generated.
2010/1/21 Sean Kelly <[email protected]>:
I got a reasonable answer by casting to int before calling abs():
import std.math, std.stdio;
void main() {
auto a = [ 4, 4, 2, 3, 2 ];
float avgdist = 0;
uint count;
foreach (i, e1; a) {
foreach (j, e2; a) {
if (i == j) continue;
if (e1 != e2) continue;
++count;
writeln("adding ", cast(int)(i - j));
avgdist += abs(cast(int)(i - j));
}
}
writeln(count, " ", avgdist / count);
}
On Jan 21, 2010, at 12:41 AM, Andrei Alexandrescu wrote:
The problem persists even if I remove the call to abs(). At least its removal
makes things look more suspicious.
Andrei
Don Clugston wrote:
2010/1/21 Sean Kelly <[email protected]>:
My first inclination would be for abs to only accept signed values. Unsigned
values don't really seem appropriate for unchecked math operations.
I agree, it doesn't make sense to take the absolute value of something
which doesn't have a sign. With range checking, it ought to be
possible to implicitly cast from uint to int, which would allow all of
the sensible uses. Unfortunately, implicit casting and templates don't
interact well. So I think abs() might need to go back to being a
non-template function.
On Jan 20, 2010, at 8:50 PM, Andrei Alexandrescu wrote:
Is there anything we can do about this?
Andrei
-------- Original Message --------
Subject: "Unsigned-related bugs never occur in real code."
Date: Wed, 20 Jan 2010 20:42:50 -0800
From: Andrei Alexandrescu <[email protected]>
Organization: Digital Mars
Newsgroups: digitalmars.D
"It's an academic problem. Don't worry about it and move on."
That's what Walter kept on telling me. Yet I've spent the better part of
an hour reducing a bug down to the following:
import std.math, std.stdio;
void main() {
auto a = [ 4, 4, 2, 3, 2 ];
float avgdist = 0;
uint count;
foreach (i, e1; a) {
foreach (j, e2; a) {
if (i == j) continue;
if (e1 != e2) continue;
++count;
avgdist += abs(i - j);
}
}
writeln(count, " ", avgdist / count);
}
May this post be an innocent victim of the war against unsigned-related
bugs.
Andrei
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