Deprecate Some from prelude

[Soni]

@steffahn

In particular if let Some(x) = ... or while let Some(y) = ... is super common

this should be in the prelude: from_fn in std::iter - Rust. (also Option has into_iter.)

@steffahn

Also note that into has problems with type inference that make it less useful than an explicit Some . E. g. you can write let x = Some(y) today, try doing this with into .

...doesn't that work fine if x is used?

warnings aren't breaking changes, but see also Option shorthand pre-pre-rfc. tl;dr: there isn't enough momentum for Into, so it's unlikely we'll ever get syntax for Into... so the solution is to encourage ppl to use Into and then there'll be momentum for Into and then there'll be syntax for Into.