【Rust】HashMap

1. new

2. 所有权

3. get

4. iterator

5. insert

6. or_insert

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1. new

let mut scores = HashMap::new();
scores.insert(String::from("Blue"), 10);

2. 所有权

let key: String = String::from("key1");
let value: String = String::from("value2");
let mut scores = HashMap::new();
// 对于像 String 这样拥有所有权的值，其值将被移动而哈希 map 会成为这些值的所有者
scores.insert(key, value);
// println!("{},{}",key,value); // key和value不再有效

3. get

let mut scores = HashMap::new();
scores.insert(String::from("name"), String::from("Tom Smith"));
let k = String::from("name");
let v: Option<&String> = scores.get(&k);
match v {
    Some(x) => println!("{}",x),
    None => println!("none value"),
}

4. iterator

let mut scores = HashMap::new();
scores.insert(String::from("name"), String::from("Tom Smith"));
for (key, value) in &scores {
    println!("{}: {}", key, value);
}

5. insert

let mut scores = HashMap::new();
scores.insert(String::from("name"), String::from("Tom Smith"));
scores.insert(String::from("name"), String::from("Tom Smith 2"));// 使用新值覆盖老值
println!("{:?}", scores);

6. or_insert

let mut scores = HashMap::new();
scores.insert(String::from("name"), String::from("Tom Smith"));
scores.entry(String::from("name")).or_insert(String::from("Tom Smith 2"));// 不存在时才插入，存在返回这个值的可变引用
println!("{:?}", scores);