Iterator adapter like std::iter::Inspect, but which passes a mutable reference to the closure

[rust-itertools]

Iterator adapter like std::iter::Inspect, but which passes a mutable reference to the closure

[bluss]

Maybe the name .map_inplace()? Could even be a win for regular mapping in some weird scenario where moves are costly and don't optimize out.

Do you have a real use case in mind? Asking because we don't want to collect nice to haves that nobody needed. (We already have enough of that in itertools.. 😞 )

[abonander]

One example came up in a possible improvement to a solution I gave in this thread on /r/rust (with your suggested naming):

fn permutations(seq: Vec<i32>) -> Vec<Vec<i32>> {
    match seq.len() {
        0 => return vec![],
        1 => return vec![seq],
        _ => (),
    }

    seq.iter().enumerate().flat_map(|(head_idx, &head)| {
        let mut remainder = seq[..head_idx].to_owned();

        if seq.len() > head_idx + 1 {
            remainder.extend(&seq[head_idx + 1..]);
        }

        permutations(remainder).map_inplace(|perm| perm.insert(0, head))
    })
    .collect()
}

However, I don't know if .map_inplace() is the best name, since mapping suggests going from one type to another. For example, Vec::map_in_place() performed the conversion T -> U where mem::size_of::<T>() == mem::size_of::<U>().

I like .edit() or .update(), myself, with .mutate() coming in a close third.

[bluss]

I like update too.

[bluss]

Implemented by @lucasem in #232 and in itertools 0.7.4!