Make it clear that .map() returns None if None.

[ameknite]

Location

https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.map

Summary

I think it would be nice if the .map() documentation made it clear that when None is consumed by .map() returns None, to make it consistent with .map_or() and .map_or_else() because right now it just says:

Maps an Option<T> to Option<U> by applying a function to a contained value.

Example in .map.or()

"Returns the provided default result (if none), or applies a function to the contained value (if any)."

https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.map_or.

and maybe add a little example like:

let x: Option<&str> = None;
assert_eq!(x.map(|s| s.len()), None);

[jyn514]

@ameknite are you interested in making a PR adding this documentation? :) there are instructions at https://rustc-dev-guide.rust-lang.org/