Support into() for filter_map (Rust 1.12)

[saschagrunert]

Hey 👋 there,

What do you think of the idea of implementing the new From for Option for some libcore functions like filter_map? The benefit would be to return just a value T instead of Some(T).

Best regards,
Sascha

[SimonSapin]

I assume you mean changing the return type of the closure in Iterator::filter_map from Option<B> to a generic O: Into<Option<B>>. The problem is that even if the return type is generic, for one given closure it has to be the same in all code paths. So any closure that sometimes returns B (taking advantage of the new From<B> for Option<B> impl) instead of Option<B> has to always do so and thus acts as if it were always returning Some(_: B). In that case there is no point in using filter_map, map could be used instead.

[saschagrunert]

Ah okay so it makes no sense in any case?

[SimonSapin]

I makes sense in that we could do it and it wouldn’t break things, but as far as I can tell it would never be useful.

[saschagrunert]

Alright, thank you for the feedback.