andThen()

[veewee]

Introduce new andThen method: https://doc.rust-lang.org/rust-by-example/error/option_unwrap/and_then.html
This method can be used to e.g. map an Option into another option:

some(1)->andThen(fn(int $value) => $value > 1 ? some($value) : none())  == none();

They apply to:

• Result
• Option
• maybe: Promise?

❗ Currently Result::then() allows returning a promise which automatically gets unwrapped. That logic should be deprecated and removed in v3 since it's rather magically. The new andThen function should be used for this purpose. We'll have to add a note for that in the code and release notes.

(to investigate: if it makes sense to keep on supporting it during runtime, but make psalm fail)

[azjezz]

(to investigate: if it makes sense to keep on supporting it during runtime, but make psalm fail)

I think that's the right way of deprecating it, as it won't break peoples code, only SA builds.