hashmap

use std::collections::HashMap;

fn main() {
    //hashmap会根据首次存放任意类型的数据
    let mut map = HashMap::new();
    map.insert(1,2);
    for (i,v) in map {
        println!("{} {}",i,v);
    }
    let mut map2 = HashMap::new();
    map2.insert(String::from("aaa"),2);
    map2.insert(String::from("bbb"),3);
    let key = String::from("aaa");
    let value = map2.get(&key);
    println!("value {:?}",value);
    println!("before update");
    for (key, value) in &map2 {
        println!("{}: {}", key, value);
    }

    println!("after update");
    //尝试插入存在则不插入
    map2.entry(String::from("aaa")).or_insert(1);
    //直接插入已存在的key则是修改
    map2.insert(String::from("bbb"),33);
    //尝试插入不存在则插入
    map2.entry(String::from("ddd")).or_insert(4);
    for (key, value) in &map2 {
        println!("{}: {}", key, value);
    }
    //map.insert(1,2);
}

1 2
value Some(2)
before update
aaa: 2
bbb: 3
after update
ddd: 4
aaa: 2
bbb: 33