Rust code shared from the playground

playground.rs

struct ATypeReturnedWithAnError;

struct IAmAnErrorType;
struct TheErrorIWant;

impl From<IAmAnErrorType> for TheErrorIWant {
    fn from(_: IAmAnErrorType) -> Self {
        unimplemented!()
    }
}

fn function_easy_error() -> Result<(), IAmAnErrorType> {
    unimplemented!()
}

fn function_less_easy_error() -> Result<(), (ATypeReturnedWithAnError, IAmAnErrorType)> {
    unimplemented!()
}

fn main() {
    let _: Result<_, TheErrorIWant> = function_easy_error().map_err(From::from);

    let _: Result<_, TheErrorIWant> = function_less_easy_error().map_err(|(_, a)| a.into());
}