[Rust 基础] 哈希 map

创建一个HashMap
类似于 vector，哈希 map 是同质的：所有的键必须是相同类型，值也必须都是相同类型。

use std::collections::HashMap;
let mut scores = HashMap::new();
scores.insert(String::from("Blue"), 10);
scores.insert(String::from("Yellow"), 50);
--------------------------------------------
use std::collections::HashMap;
let teams  = vec![String::from("Blue"), String::from("Yellow")];
let initial_scores = vec![10, 50];
let scores: HashMap<_, _> = teams.iter().zip(initial_scores.iter()).collect();

[

哈希 map 和所有权

](https://kaisery.github.io/trpl-zh-cn/ch08-03-hash-maps.html#%E5%93%88%E5%B8%8C-map-%E5%92%8C%E6%89%80%E6%9C%89%E6%9D%83)`i32` 这样的实现了 Copy trait 的类型，其值可以拷贝进哈希 map
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[

use std::collections::HashMap;
let field_name = String::from("Favorite color");
let field_value = String::from("Blue");
let mut map = HashMap::new();
map.insert(field_name, field_value);
// 这里 field_name 和 field_value 不再有效，
// 尝试使用它们看看会出现什么编译错误！

](https://kaisery.github.io/trpl-zh-cn/ch08-03-hash-maps.html#%E5%93%88%E5%B8%8C-map-%E5%92%8C%E6%89%80%E6%9C%89%E6%9D%83)

访问哈希map的值

use std::collections::HashMap;
let mut scores = HashMap::new();
scores.insert(String::from("Blue"), 10);
scores.insert(String::from("Yellow"), 50);
let team_name = String::from("Blue");
let score = scores.get(&team_name);

遍历哈希map的值

use std::collections::HashMap;
let mut scores = HashMap::new();
scores.insert(String::from("Blue"), 10);
scores.insert(String::from("Yellow"), 50);
for (key, value) in &scores {
    println!("{}: {}", key, value);
}

[

更新哈希 map

](https://kaisery.github.io/trpl-zh-cn/ch08-03-hash-maps.html#%E6%9B%B4%E6%96%B0%E5%93%88%E5%B8%8C-map)[

覆盖一个值

](https://kaisery.github.io/trpl-zh-cn/ch08-03-hash-maps.html#%E8%A6%86%E7%9B%96%E4%B8%80%E4%B8%AA%E5%80%BC)[

use std::collections::HashMap;
let mut scores = HashMap::new();
scores.insert(String::from("Blue"), 10);
scores.insert(String::from("Blue"), 25);
println!("{:?}", scores);

](https://kaisery.github.io/trpl-zh-cn/ch08-03-hash-maps.html#%E6%9B%B4%E6%96%B0%E5%93%88%E5%B8%8C-map)[ ](https://kaisery.github.io/trpl-zh-cn/ch08-03-hash-maps.html#%E8%A6%86%E7%9B%96%E4%B8%80%E4%B8%AA%E5%80%BC)[

只在键没有对应值时插入

](https://kaisery.github.io/trpl-zh-cn/ch08-03-hash-maps.html#%E5%8F%AA%E5%9C%A8%E9%94%AE%E6%B2%A1%E6%9C%89%E5%AF%B9%E5%BA%94%E5%80%BC%E6%97%B6%E6%8F%92%E5%85%A5)[

](https://kaisery.github.io/trpl-zh-cn/ch08-03-hash-maps.html#%E8%A6%86%E7%9B%96%E4%B8%80%E4%B8%AA%E5%80%BC)[```rust use std::collections::HashMap;

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

scores.entry(String::from(“Yellow”)).or_insert(50); scores.entry(String::from(“Blue”)).or_insert(50);

println!(“{:?}”, scores);

](https://kaisery.github.io/trpl-zh-cn/ch08-03-hash-maps.html#%E6%9B%B4%E6%96%B0%E5%93%88%E5%B8%8C-map)[<a name="79a8ebab"></a>
#### 根据旧值更新一个值
](https://kaisery.github.io/trpl-zh-cn/ch08-03-hash-maps.html#%E6%A0%B9%E6%8D%AE%E6%97%A7%E5%80%BC%E6%9B%B4%E6%96%B0%E4%B8%80%E4%B8%AA%E5%80%BC)[<a name="d41d8cd9-1"></a>
#### 
](https://kaisery.github.io/trpl-zh-cn/ch08-03-hash-maps.html#%E8%A6%86%E7%9B%96%E4%B8%80%E4%B8%AA%E5%80%BC)如果是第一次看到某个单词，就插入值 `0`[<a name="d41d8cd9-2"></a>
#### 
](https://kaisery.github.io/trpl-zh-cn/ch08-03-hash-maps.html#%E8%A6%86%E7%9B%96%E4%B8%80%E4%B8%AA%E5%80%BC)[```rust
use std::collections::HashMap;
let text = "hello world wonderful world";
let mut map = HashMap::new();
for word in text.split_whitespace() {
    let count = map.entry(word).or_insert(0);
    *count += 1;
}
println!("{:?}", map);

](https://kaisery.github.io/trpl-zh-cn/ch08-03-hash-maps.html#%E6%9B%B4%E6%96%B0%E5%93%88%E5%B8%8C-map)