Please provide a FromIterator impl

[joshtriplett]

fst has all the necessary infrastructure for FromIterator to work; please consider implementing it, so that collect works, and in particular to make it easy to collect into Result<Fst, ...> or Result<Set, ...>.

Thank you!

[BurntSushi]

It's not clear to me that this is a good idea. Is there any precedent for implementing FromIterator for fallible operations? As an example, Set::from_iter already exists, but note that it returns a Result. That is, you cannot construct a Set from any iterator. The keys must be lexicographically sorted. So as far as I can see, there are only two possible implementations for FromIterator:

• Consume the iterator into memory, sort the keys and then build the set.
• Panic if the iterator yields an unsorted key.

Neither option seems particularly good to me.

[joshtriplett]

Yes, there's precedent for fallible FromIterator; that's what allows .collect::<Result<Vec<_>, SomeError>().

[BurntSushi]

Sure, but that only works because of a blanket impl on Result itself. Which means you can't implement FromIterator<Vec<u8>> for Result<Fst<Vec<u8>>, fst::Error>. Unless I'm missing something. If so, can you show me how? I don't see it.

Playground: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=e997d571f41f88f3eba30660ee7b4429

Do you know of any FromIterator impls that are themselves fallible? I can't think of any off the top of my head in std. And a quick glance of the impls of FromIterator in std doesn't seem to show any. For example, if fallible FromIterator impls were allowed, then I'd expect to see a FromIterator<u8> for String, but I don't think such a thing can exist (without panicking or doing lossy decoding).