散列表 HashMap
vector 通过整型索引来存储值,而 HashMap
(散列表)通过键(key)来存储值。HashMap
的键可以是布尔型、整型、字符串,或任意实现了 Eq
和 Hash
trait 的其他类型。在下一节将进一步介绍。
和 vector 类似,HashMap
也是可增长的,但 HashMap 在空间多余时能够缩小自身(原文:HashMaps can also shrink themselves when they have excess space. )。创建 HashMap,可以使用适当的初始化容器(starting capacity) HashMap::with_capacity(unit)
,或者使用 HashMap::new()
来获得一个带有默认初始容器的 HashMap(推荐方式)。
use std::collections::HashMap; fn call(number: &str) -> &str { match number { "798-1364" => "We're sorry, the call cannot be completed as dialed. Please hang up and try again.", "645-7689" => "Hello, this is Mr. Awesome's Pizza. My name is Fred. What can I get for you today?", _ => "Hi! Who is this again?" } } fn main() { let mut contacts = HashMap::new(); contacts.insert("Daniel", "798-1364"); contacts.insert("Ashley", "645-7689"); contacts.insert("Katie", "435-8291"); contacts.insert("Robert", "956-1745"); // 接受一个引用并返回 Option<&V> match contacts.get(&"Daniel") { Some(&number) => println!("Calling Daniel: {}", call(number)), _ => println!("Don't have Daniel's number."), } // 如果被插入的值为新内容,那么 `HashMap::insert()` 返回 `None`, // 否则返回 `Some(value)` contacts.insert("Daniel", "164-6743"); match contacts.get(&"Ashley") { Some(&number) => println!("Calling Ashley: {}", call(number)), _ => println!("Don't have Ashley's number."), } contacts.remove(&("Ashley")); // `HashMap::iter()` 返回一个迭代器,该迭代器获得 // 任意顺序的 (&'a key, &'a value) 对。 // (原文:`HashMap::iter()` returns an iterator that yields // (&'a key, &'a value) pairs in arbitrary order.) for (contact, &number) in contacts.iter() { println!("Calling {}: {}", contact, call(number)); } }
了解更多关于映射(map)和散列映射(hash map)(通常也称作散列表,哈希表)的实现原理,可以查看 Wikipedia 的词条散列表。