and_modify method should be part of the HashMap's Documentation.

[SeniorMars]

I understand that and_modify deals with the Entry enum; however, I believe the method would be advantageous to developers when dealing with HashMaps.

A common pattern I see when using hashmaps is something like this:

strings.into_iter().for_each(|string| {
    let value = map.entry(string).or_insert(0);
    *value += 1;
});

However, with and_modify this turns into this:

strings.into_iter().for_each(|string| {
    map.entry(string)
        .and_modify(|value| *value += 1)
        .or_insert(1);
});

Which leans more into idiomatic rust. I just learned of and_modify today, and I believe more rust users would use it if they knew it existed. I think the problem is that and_modify is part of the Entry API.

[eggyal]

To be clear, are you suggesting that the documentation for HashMap::entry should include an example using and_modify? That seems pretty reasonable.

@rustbot label +A-docs +E-easy

[SeniorMars]

Yes, I am. Can I work on the PR for the issue? Thanks!

[SeniorMars]

@rustbot claim

[SkiFire13]

strings.into_iter().for_each(|string| {
    let value = map.entry(string).or_insert(0);
    *value += 1;
});

I would shorten this to:

strings.into_iter().for_each(|string| {
    *map.entry(string).or_insert(0) += 1;
});

IMO this is more idiomatic than the and_modify example, but this is probably subjective. It just seems more linear and thus simplier to me:

• if an entry is empty the default value is 0 (this is in addition to what normally happens)
• then increase it (this always happens)

In contrast with and_modify:

• if there's an entry increase it (which is conditional on not being the first element)
• else set it to 1 (which is condition to being the first element)

Anyway with #98125 I suppose this could be closed?

[SeniorMars]

So honestly, I agree with what you are saying! However, if we look at the HashMap documentation right now we see this:

// update a key, guarding against the key possibly not being set
let stat = player_stats.entry("attack").or_insert(100);
*stat += random_stat_buff();

I believe that and_modfiy should be used for this type of example. However, for the example I gave which was not the best I admit, I agree that it would be simpler than to do it in one liner.