For reference, this topic was discussed last August as well: https://mail.mozilla.org/pipermail/rust-dev/2013-August/005113.html
On Thu, Feb 13, 2014 at 10:05 AM, Simon Sapin <simon.sa...@exyr.org> wrote: > Hi, > > The Rust documentation currently makes iterators behavior undefined after > .next() has returned None once. > > http://static.rust-lang.org/doc/master/std/iter/trait.Iterator.html >> >> The Iterator protocol does not define behavior after None is >> returned. A concrete Iterator implementation may choose to behave >> however it wishes, either by returning None infinitely, or by doing >> something else. > > > http://static.rust-lang.org/doc/master/guide-container.html >> >> In general, you cannot rely on the behavior of the next() method >> after it has returned None. Some iterators may return None forever. >> Others may behave differently. > > > > This is unfortunate. Code that accepts any iterator as input and does with > it anything more complicated than a single 'for' loop will have to be > defensive in order to not fall into undefined behavior. > > The type system can not enforce anything about this, but I'd like that we > consider having conventions about "well-behaved" iterators. > > --- > > 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. > > 1. Iterators *should* be well-behaved. > > 2. Iterators in libstd and other libraries distributed with rustc *must* be > well-behaved. (I.e. not being well-behaved is a bug.) > > 3. When accepting an iterator as input, it's ok to assume it's well-behaved. > > 4. For iterator adaptors in particular, 3. means that 1. and 2. only apply > for well-behaved input. (So that, eg. std::iter::Map can stay as > straightforward as it is, and does not need to be coded defensively.) > > --- > > Does the general idea sound like something y'all want? I'm not overly > attached to the details. > > -- > Simon Sapin > _______________________________________________ > Rust-dev mailing list > Rust-dev@mozilla.org > https://mail.mozilla.org/listinfo/rust-dev _______________________________________________ Rust-dev mailing list Rust-dev@mozilla.org https://mail.mozilla.org/listinfo/rust-dev
