Rust 如何使BTreeMap:：get返回字符串？

函数的

get（）

返回一个

选项

类型，该类型引用与键对应的值。因此，您在堆上存储了一个

字符串

，此函数根据键返回对该

字符串的引用

我把你的例子缩短了一点。您有一个未初始化的
BTreeMap
，所以我首先初始化了它-
让mut-map:BTreeMap=BTreeMap:：new（）。在您的情况下，您可以轻松地使用
if let
语句

src/main.rs:5:24: 5:39 error: mismatched types:
 expected `collections::string::String`,
    found `core::option::Option<&collections::string::String>`
(expected struct `collections::string::String`,
    found enum `core::option::Option`) [E0308]
src/main.rs:5     let name: String = map.get("name");
                                     ^~~~~~~~~~~~~~~
src/main.rs:5:24: 5:39 help: run `rustc --explain E0308` to see a detailed explanation
error: aborting due to previous error
Could not compile `hello_world`.

src/main.rs:5:24: 5:39 error: mismatched types:
 expected `collections::string::String`,
    found `core::option::Option<&collections::string::String>`
(expected struct `collections::string::String`,
    found enum `core::option::Option`) [E0308]
src/main.rs:5     let name: String = map.get("name");
                                     ^~~~~~~~~~~~~~~
src/main.rs:5:24: 5:39 help: run `rustc --explain E0308` to see a detailed explanation
error: aborting due to previous error
Could not compile `hello_world`.

use std::collections::BTreeMap;

fn main() {
    let mut map: BTreeMap<String, String> = BTreeMap::new();
    map.insert("name".into(), "aho".into());

    if let Some(name) = map.get("name") {
        println!("welcome, {}", name);
    } else {
        println!("welcome, stranger");
    }
}

use std::collections::BTreeMap;

fn main() {
    let mut map: BTreeMap<String, String> = BTreeMap::new();
    map.insert("name".into(), "aho".into());

    if let Some(name) = map.get("name") {
        let name: String = name.clone();
        println!("welcome, {}", name);
    } else {
        println!("welcome, stranger");
    }
}