Question on holding related data in a struct.
from modulus@lemmy.ml to rust@programming.dev on 25 Mar 2024 11:14
https://lemmy.ml/post/13621174
from modulus@lemmy.ml to rust@programming.dev on 25 Mar 2024 11:14
https://lemmy.ml/post/13621174
I have a struct that looks like this:
pub struct Game {
/// A HashSet with the players waiting to play as account strings.
lobby: HashSet<String>,
/// capacity determines how many people a match contains.
capacity: u8,
/// A vector of ongoing matches.
matches: Vec<Match>,
/// HashSet indicating for each player which match they are in.
players: HashMap<String, usize>,
}
I realised that this won’t work because if there are 3 matches (0, 1, 2) and I remove 1 because it ends, the players that used to point at 2 will be pointing outside the vector or to an incorrect match.
So I thought the obvious solution was to use a reference to the match: players: HashMap<String, &Match>. But this makes lifetimes very complicated.
What’s a good way to deal with a case like these where data are interrelated in the same struct?
threaded - newest
You could store the matches in a
HashMapas well, using someMatchIdtype as the key, i.e.,HashMap<MatchId, Match>. Then you can use that as the reference inplayers: HashMap<String, MatchID>. Only downside is that you have to generate uniqueMatchIds, e.g., by using some counter.This is exactly the use case that slotmap is meant for. I highly recommend using the library rather than reinventing the concept.
Ah, that does seem like it will solve the problem. Thanks!
I don’t think there is a good way of having references within the same struct, but you could store reference counted matches:
You would still have to make sure that the
playersmap is updated, maybe weak references are useful there.Maybe you could also consider storing the players of a match in the match itself, not outside.
Thanks, the RC is a possible approach. It seems to violate DRY a bit but maybe there’s no way around it.
The reason I had the players outside the match is that I need them there anyway, because when I get a player action I need to check in which match they are, who are their opponent(s) and so on. So even if they’re in, they’ll have to be out too as there are concurrent matches and the player actions come all through the same network stream.
Could you not have a hashmap keyed on matches pointing to vectors of strings for the players in each match? Basically modeling the data how you want rather than relying on indexing.
Not sure I understand. What I’m trying to do is something like this:
So what I have as a key is a player name (AP username) and from that I need to find which match they’re in.
There’s nothing semantically useful about a match ID.
If you instead made your
lobbyfield aHashMap<String, MatchId>, then whenever you get an event from a known player, you can lookup the match they are in from the lobby map and use that to lookup other data about the match (such as the other players) via thematchesfield (assuming that was also changed to be a hashmap as described in my previous comment)..