Possible improvement for hashmaps3

[YDX-2147483647]

Problem & possible solution

hashmaps3 plays a scores table using scores: HashMap<String, Team>, where Team: { name: String, … } — both the key and the value describe the team name, leading to the ownership puzzle mentioned in #1074. (See below)

I think we should refactor the map: “team name ↦ scores” or “team ↦ scores”, instead of “team name ↦ team and scores”.

// After refactoring
let board_1 = scores.entry(team_1_name)
    .or_insert(ScoreBoard {
        goals_scored: 0,
        goals_conceded: 0,
    });
board_1.goals_scored += team_1_score;
board_1.goals_conceded += team_2_score;

The ownership puzzle

To be specific, there are two solutions here currently.

1. Use scores.entry(…).or_insert(…).

   Graceful, but most of the clones are redundant. (Only the first time is necessary.)

   let team_1 = scores.entry(team_1_name.clone())
       .or_insert(Team {
           name: team_1_name.clone(),
           goals_scored: 0,
           goals_conceded: 0,
       });
   team_1.goals_scored += team_1_score;
   team_1.goals_conceded += team_2_score;
   

   Remark: If you don’t clone for entry(), you have nothing to set name in or_insert().

2. Manually get, check and insert.

   It only clones when necessary, but becomes more complicated.

   let team_2 = match scores.get_mut(&team_2_name) {
       Some(team) => team,
       None => {
           scores.insert(
               team_2_name.clone(),
               Team {
                   name: team_2_name.clone(),
                   goals_scored: 0,
                   goals_conceded: 0,
               },
           );
           scores.get_mut(&team_2_name).unwrap()
       }
   };
   team_2.goals_scored += team_2_score;
   team_2.goals_conceded += team_1_score;
   

Or using if let.

---

Besides, storing two team names for each team can be confusing. If two names conflict with each other, which should be taken?

[YDX-2147483647]

Related: #1160

[Ben2917]

I believe this merged PR closes this issue: https://github.com/rust-lang/rustlings/pull/1547

[YDX-2147483647]

Thank you for remind me! I agree. Let's close it.