Is it possible to convert the option <Result <T, E >> to the result <Option <T>, E> without using a match?

Question

My first thought is the map Option , but I cannot use try! from inside closure. The match statement seems unnecessary, but I cannot figure out how to simplify it.

 fn example<T, E>(val: Option<Result<T, E>>) -> Result<Option<T>, E> { Ok(match val { Some(v) => Some(v?), None => None }) } 

Answer 1

You can use Option::map_or() :

 val.map_or(Ok(None), |v| v.map(Some)) 

Answer 2

In Rust 1.33, transpose() is stable, so you can just call it:

 fn main() { let x: Result<Option<i32>, ()> = Ok(Some(5)); let y: Option<Result<i32, ()>> = Some(Ok(5)); assert_eq!(x, y.transpose()); }