On Mon, 19 Sep 2011 23:09:45 +0100, Simen Kjaeraas
<[email protected]> wrote:
On Mon, 19 Sep 2011 23:20:47 +0200, bearophile
<[email protected]> wrote:
A tiny puzzle I've shown on IRC. This is supposed to create an inverted
array of cards, but what does it print instead?
import std.stdio, std.algorithm, std.range;
void main() {
int[52] cards;
copy(iota(cards.length - 1, -1, -1), cards[]);
writeln(cards);
}
Gawds, that's an ugly bug. For those who can't spot it,
typeof(cards.length) == uint, hence -1 is converted to a uint
(4_294_967_295, to be exact). iota then says 'that's fine, I'll just
return an empty range for you.'
Solution: knock some sense into integral promotion rules.
Workaround: cast(int)cards.length.
What was the rationale for having unsigned array lengths, again?
Well.. logically it makes sense as arrays cannot have negative lengths,
but practically, this bug is what happens as a result. This is the reason
I typically use signed int for lengths, unless I expect the length to
exceed max signed int. It's also a good idea if you ever do any
subtraction/calculation with them, as you don't want to underflow to max
signed int ever. It means that in my daily work I have to cast the return
value of strlen() everywhere (cos my compiler complains, but only in 64
bit mode..).. I mean, really, when are you going to have a string which is
longer than max signed int?! It's just nonsensical.
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