Syntax for returning early with an error

language design
62

Actually if one were to make enum variants first class types, then this special casing could be done cleanly, and even let x = Err(1); x? would be a terminator, as x would be inferred of type Result::Err instead of Result, and then Result::Err could implement a new "TryResidual" trait that would trigger the behavior.

I think this requires a new edition though as I think it's not backward compatible to make this inference change in general, but it might actually be a viable solution, perhaps (for older editions, macros or functions could be provided that produces the enum variant explicitly).

63

I think that with never_type we already got all we need. No need for anything fancy/new/involving-editions/etc…

#![feature(never_type)]

fn yeet<E>(e: E) -> Result<!, E> {
    Err(e)
}

fn foo() -> Result<i32, bool> {
    yeet(false)?;
    // unreachable
}

(playground)

3 Likes
64

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