Rename Option::chain to Option::flat_map

[hanny24]

Option is a (special) kind of collection, thus we should provide an interface that as similar to the interface of vec (which has flat_map) as possible.

[brson]

Same for Result?

[hanny24]

Yes, that makes sence as well.

[huonw]

FWIW, many other things have a similar operation to chain (it's precisely a monadic bind, i.e. >>= operator from Haskell) but it makes little-to-no sense to call it flat_map, e.g. Futures. (I think it's quite a stretch even for Result.)

That said, there is quite possibly a precedent (other than just for vectors) for calling this operation flat_map rather than bind or chain; I don't know.

[huonw]

Triage: no progress that I know of: everything is still called chain.

[huonw]

Err, oops; I was incorrect: we've renamed Option.chain and Result.chain to and_then.

[catamorphism]

Nominating so we can discuss the naming.

[hexsel]

It is, to a certain degree a matter of opinion of course, but coming from Scala, it's nice to get a collection of Options and flatMap them into a collection of results, dropping the Nones in the process.

What I mean by that is that it is interesting to treat Option as a collection of 0-1 elements as hanny24 suggested (not what the specific method names are).

[huonw]

@hexsel already possible, due to the Option.iter method.

[pnkfelix]

declined and closing; leaving things as they are.