pub trait Branch {
    type Output;
    type Residual;
    fn branch(self) -> ControlFlow<Self::Residual, Self::Output>;
}
pub trait FromOutput<O = <Self as Branch>::Output>: Branch {
    fn from_output(output: O) -> Self;
}
pub trait FromResidual<R = <Self as Branch>::Residual>: Branch {
    fn from_residual(residual: R) -> Self;
}
pub trait Try = Branch + FromResidual + FromOutput;
pub trait Residual<O>: Sized {
    type TryType: Try<Output = O, Residual = Self>;
}

impl<'a, T, E> Branch for &'a Result<T, E> {
    type Output = &'a T;
    type Residual = Result<Infallible, &'a E>;

    fn branch(self) -> ControlFlow<Self::Residual, Self::Output> { … }
}

fn as_ref<R>(x: R) -> <R::Residual as Residual<<R as Branch>::Output>>::TryType
where
    R: Branch<Residual: Residual<<R as Branch>::Output>>
 { …  }

let x: Result<&i32, &()> = as_ref(&Ok::<i32, ()>(1));