Comment by saghm

I'm fortunate enough not to have to often write code in other languages anymore, but my experience that writing code in ways that satisfies the compiler actually ends up being code I prefer anyhow. I was somewhat surprised at the first example because I haven't run into something like that, but it's also not really the style I would write that function personally (I'm not a big fan of repetitions like having `Some(x)` repeated both as a capture pattern and a return value), so on a whim I tried what would have been the way I'd write that function, and it doesn't trigger the same error:

    fn double_lookup_mut(map: &mut HashMap<String, String>, mut k: String) -> Option<&mut String> {
        map.get_mut(&k)?;
        k.push_str("-default");
        map.get_mut(&k)
    }

I wouldn't have guessed that this happened to be a way around a compiler error that people might run into with other ways of writing it; it just genuinely feels like a cleaner way for me to implement a function like that.