rust data struct説明--HashMap

New HashMap

 std::collections::HashMap使用方法

１create new hashmap

use std::collections::HashMap
let mut scores = hashmap::new()

2 insert value into hashmap

scores.insert(key,value)

3 get value

onwerkey = String::from(key)
scores.get(&onwerkey)

4 Hash Mapの完全使用方法

use std::collections::HashMap;


//#[derive(Hash)] attribute is used to automatically generate a Hash implementation for a struct or an enum.
#[derive(Hash)]
struct Persion {
    first_name: string,
    last_name: String,
}

impl Person {
    fn new(first: &str, last: &str) -> Self {
        Person {
            first_name; first.to_string(),
            last_name: last.to_string(),
        }
    }
}

fn main() {
    let mut book = HashMap::new();
    book.insert(Person::new("John","smith","521-8976"));
    book.insert(Person::new("sandra","dee","521-9655"));
    book.insert(Person::new("Ted","smith","418-4165"));

    let P = Person::new("John","Smith");
    if let Some(phone) = book.get(&p) {
        //find the book that person haved
        println!("Phone number found: {}", phone);
    }
    //delete recode
    book.remove(&p)

    println!("Find Key:{}",book.contains_key(&p));




}

５ entry Apiの使用と基本使用の違う

// 基本使用,2回操作、１キーの確認２キーを増加
if map.contains_key(key) {
    map.insert(key,value);
}

//entry apiの使用
map.entry(key).or_insert(value)

6 hashmap中にキーの変更がダメです

use std::hash::{Hash, Hasher};
use std::collections::HashMap;
use std::cell::Cell;

#[derive(Eq, PartialEq)]
struct BadKey {
    value: Cell<i32>
}

impl BadKey {
    fn new(v: i32) -> Self {
        BadKey { value: Cell::new(v)}
    }
}

impl Hash for BadKey {
    fn hash<H: Hasher>(&self, state: &mut H){
        self.value.get().hash(state);
    }
}
fn main() {
    let mut map = HashMap::new();
    map.insert(BadKey::new(1),100);
    map.insert(BadKey::new(2),200);
    for key in map.keys() {
        key.value.set(key.value.get() * 2);
    }
    println!("Find key 1:{:?}",map.get(&BadKey::new(1)));
    println!("Find key 2:{:?}",map.get(&BadKey::new(2)));
    println!("Find key 4:{:?}",map.get(&BadKey::new(4)));

}
//response
//Find key 1:None
//Find key 2:None
//Find key 4:None

結果;変更のキーと変更しないのキーは探さない、その原因でkeyはdynamic keyはダメです

７ 存在のリストを付いて、Hash Mapを作成します

                                                                                                                                                 

use std::collections::HashMap;
let solar_distance = HashMap::from([
    ("Mercury", 0.4),
    ("Venus", 0.7),
    ("Earth", 1.0),
    ("Mars", 1.5),
]);

8別の方法

use std::collections::HashMap;
let a  = HashMap::new()

a.is_empty()
a.len()
//
a.drain().drain()(.take(1)
a.keys()
a.containers_key()
a.remove(&mut value) --> Removes a key from the map, returning the value at the key if the key was previously in the map.
a.remove_entry(&Mut value) -->Removes a key from the map, returning the stored key and value if the key was previously in the map.