On 04/03/2014 13:23, Tommi wrote:
On Thu, Feb 13, 2014 at 10:05 AM, Simon Sapin <simon.sa...@exyr.org
<mailto:simon.sa...@exyr.org>> wrote:
Proposal:
0. An iterator is said to be "well-behaved" if, after its .next()
method has
returned None once, any subsequent call also returns None.
I agree with the spirit of your proposal. But I would change that first
clause above to read:
/An iterator is said to be "well-behaved" when its .next() method always
returns None if the iterator logically has no elements to iterate over./
"No elements to iterate over" is already what None is supposed to mean,
so this doesn’t add anything.
And all iterators should, by convention, be well-behaved. Otherwise it's
impossible to pinpoint what exactly is the bug in the following code:
struct Digits {
n: int
}
impl Iterator<int> for Digits {
fn next(&mut self) -> Option<int> {
self.n += 1;
if self.n == 10 {
None
}
else {
Some(self.n)
}
}
}
I don’t see what’s unclear here. This is the canonical example of an
ill-behaved iterator. This code is buggy, `self.n` should only be
incremented when returning Some().
--
Simon Sapin
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