Is there plan to add `Result<T, E>.expect_err` method?

[FuGangqiang]

Result<T, E> has unwrap and expect method yielding Ok,
but only has unwrap_err yielding Err, there isn't expect_err method.

[abonander]

Not enough demand, maybe? Rust follows a minimalist philosophy: the standard library doesn't try to cover all possible use-cases, only the ones that appear to be the most common.

That said, this sounds like it could be pretty useful, especially in unit tests that are expecting failure. I don't see any mention of an expect_err counterpart on the discussion for the original Result::expect() RFC. I guess no one thought to consider it.

If you want to try drafting an RFC to propose adding Result::expect_err(), this is a good place to start. It's common practice to post the draft on https://internals.rust-lang.org first to get feedback on it.

[steveklabnik]

Triage: today, small additions like this don't need a full RFC, just a PR. @FuGangqiang if you (or anyone else) would like to send a PR in for this, it can be discussed there. But since this is a small request and nobody has commented in over a year, I'm going to give this issue a close. Thanks!