rust - 如何传递具有特征的 Arc 作为引用？

Question

如何传递对 Arc<A> 的引用以便以下代码编译成功？

use std::sync::Arc;

trait A {
    fn send(&self);
}

struct B;
impl A for B {
    fn send(&self) {
        println!("SENT");
    }
}

fn ss(a: &Arc<A>) {
    let aa = a.clone();
    aa.send();
}

fn main() {
    let a = Arc::new(B);
    ss(&a);
}

( playground )

如果我省略引用，它可以编译，但 Clippy 警告我在这种情况下 in 是没有意义的。

code without reference 上的 Clippy 错误:

  Compiling playground v0.0.1 (file:///playground)
warning: this argument is passed by value, but not consumed in the function body
  --> src/main.rs:13:10
   |
13 | fn ss(a: Arc<A>) {
   |          ^^^^^^ help: consider taking a reference instead: `&Arc<A>`
   |
   = note: #[warn(needless_pass_by_value)] on by default
   = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.186/index.html#needless_pass_by_value

Answer 1

您可以改为传递对 Arc 内容的引用。

fn ss(a: &A) {
    a.send();
}

fn main() {
    let a = Arc::new(B);
    ss(&*a);
}