Pre-RFC: Catching Functions

language design
70

I like idea behind throw, but T catch E as a sugar for Result<T, E> looks quite unnecessary to me and hides enum nature of error handling, which I think will hurt learnability. The only case for which it looks a bit useful is when return type is Result<(), E>, but I am not sure if it’s enough for such addition. Also as was noted by others usage of throw/catch will probably be a big source of confusion for newcommers. Same goes for Ok wrapping, while I too don’t like Ok(()) that much, I don’t think that hiding it behind magic is a good idea, especially considering that this behaviour will be non-generic.

I would like to have instead two new keywords (lets call them reta and retb for now) which will work in conjunction with this trait:

trait RetTrait {
    type A;
    type B;

    fn reta(val: Self::A) -> Self;
    fn retb<V: Into<Self::B>>(val: V) -> Self;
}

impl<T, E> RetTrait for Result<T, E> {
    type A = T;
    type B = E;
    
    fn reta(val: Self::A) -> Self {
        Ok(val)
    }
    
    fn retb<V: Into<Self::B>>(val: V) -> Self {
        Err(val.into())
    }
}

So if we’ll write reta 1; in case of Result it will be sugar for return Ok(1); and retb "error text"; will be sugar for return Err(From::from("error text"));. And it can be easily extended to other types.

2 Likes