3
我想写一个参数化功能if_found_update
如果存在的话,在哈希更新的值:DEREF强制使用泛型
use std::collections::HashMap;
fn if_found_update<K, V>(data: &mut HashMap<K, V>, k: &K, v: &V, f: &Fn(&V, &V) -> V) -> bool
where K: std::cmp::Eq,
K: std::hash::Hash
{
if let Some(e) = data.get_mut(k) {
*e = f(e, v);
return true;
}
false
}
fn main() {
let mut h: HashMap<String, i64> = HashMap::new();
h.insert("A".to_string(), 0);
let one = 1 as i64;
fn update(e1: &i64, e2: &i64) -> i64 {
e1 + e2
};
let k: &str = &"A".to_string();
println!("{}",
if_found_update(&mut h, &"A".to_string(), &one, &update)); // works
println!("{}", if_found_update(&mut h, k, &one, &update)); // fails to compile
}
if_found_update(&mut h, &"A".to_string(), &one, &update);
工作正常,但if_found_update(&mut h, k, &one, &update)
失败,编译:
error[E0308]: mismatched types
--> src/main.rs:24:44
|
24 | println!("{}", if_found_update(&mut h, k, &one, &update)); // fails to compile
| ^expected struct `std::string::String`, found str
|
= note: expected type `&std::string::String`
= note: found type `&str`
我认为这是因为它没有适当的deref强制。有没有办法让这样的事情发挥作用?
谢谢!我尝试过'借用',但我没有正确使用它。 – divbyzero