Why can I call .iter() on an immutable empty array?

[scottmcm]

@bes

intellectually I think indexing should return an Option unless statically provable

"Bad person" is definitely too strong. Of late I've been talking about places with algorithmic invariants as being where dogmatically returning Option/Result can hurt more than it helps. That's not unlike what you said about "statically provable", but acknowledging that actually putting that proof machinery in the language may be impractical.

Related previous conversations:

Why does rust have [ ] indexing?

While it's important to offer a way to do things that doesn't panic, it's also important to think about what people will realistically do on errors. If something like 99% of the time people will just say "shut up compiler; I checked that already", then it can actually be better for the short-named one to be the panicking one, with a separate try_blah-style method available as an option. Note that this is generally only true when it's easy to http://wiki.c2.com/?LookBeforeYouLeap -- like it is …

Or, more generally, To panic or to Result - #4 by scottmcm