rust two ways

v1.rs

use std::collections::HashMap;

#[derive(Hash, Eq, PartialEq, Debug)]
struct Item {
    rank: u32,
    revision: u32,
}

fn should_insert(item: &Item, acc: &HashMap<u32, Item>) -> bool {
    match acc.get(&item.rank) {
        Some(existing) if existing.revision < item.revision => true,
        None => true,
        _ => false,
    }
}

fn main() {
    let data = vec![
        Item { rank: 1, revision: 1 },
        Item { rank: 0, revision: 1 },
        Item { rank: 4, revision: 1 },
        Item { rank: 1, revision: 2 },
        Item { rank: 0, revision: 2 },
        Item { rank: 3, revision: 1 },
    ];

    let mut result: HashMap<u32, Item> = HashMap::new();

    for item in data {
        if should_insert(&item, &result) {
            result.insert(item.rank, item);
        }
    }
    
    println!("{:?}", result);
}

v2.rs

use std::collections::HashMap;

#[derive(Hash, Eq, PartialEq, Debug)]
struct Item {
    rank: u32,
    revision: u32,
}

fn main() {
    let data = vec![
        Item { rank: 1, revision: 1 },
        Item { rank: 0, revision: 1 },
        Item { rank: 4, revision: 1 },
        Item { rank: 1, revision: 2 },
        Item { rank: 0, revision: 2 },
        Item { rank: 3, revision: 1 },
    ];

    let mut result: HashMap<u32, Item> = HashMap::new();

    for item in data {
        // Decide if item should be kept or discarded
        let to_insert = match result.get(&item.rank) {
            // Mark item for insert if key exists and revision is greater than existing
            Some(existing) if existing.revision < item.revision => Some(item),
            // or if key doesn't exist yet
            None => Some(item),
            // otherwise discard
            _ => None,
        };
        // Insert item if marked
        if let Some(new_item) = to_insert {
            result.insert(new_item.rank, new_item);
        }
    }
    
    println!("{:?}", result);
}