yosh

Wrote down another one I ran into last week - Rust's `.unwrap_or()` methods: https://github.com/yoshuawuyts/papercuts/blob/master/2018-05-16-rust-or-else.md …

`unwrap_or` can't return a Result because that wouldn't be unwrapped­. it sounds like `or_else()?` might be a good fit though? `self.cache.get(key).or_else(|| self.db.get(key))?`

It's not because its always executed, which defeats the purpose. I cover both versions in the post - perhaps it wasn't being clear enough :/

`or_else` takes a closure which is only executed if the Result is an Err and which returns a new Result. i think it's actually the same as your `unwrap_or_result` idea https://doc.rust-lang.org/std/result/enum.Result.html#method.or_else …

Ahhhh, yes okay - that looks a lot closer! Looks like it only applies to Result types though, not Option types. So still don't think it would solve this case. But it's getting closer!

Option has or_else which you can return another Option from, and `ok_or_else(fn)` which turns an Option<T> into a Result<T, E> in a similar way https://doc.rust-lang.org/std/option/enum.Option.html#method.ok_or_else …

Yeah, but I'm still not seeing any way where we can handle errors inside the None branch. How would the initial example be expressed with these statements? I feel like I'm missing something obvious?

let node = self.cache.get(key) // Option<K> .ok_or_else(|| self.db.get(key))?; // Result<K, E> can be ?-ed // node is now a K