Clone 是 Rust 编程语言中一个核心特质（trait）， 定义了类型如何安全、明确地创建其值的深拷贝（deep copy）。
下面用实例来演示Clone的作用，先看一下如下的代码，注意此代码编译不过。
#[derive(Debug)]
struct Item{value: i32,
}fn main() {let a = Item{value:7};let b = a;println!("value a {:?}, value b {:?}", a, b);
}编译报错：
cargo run
error[E0382]: borrow of moved value: `a`
--> src/main.rs:10:44
|
8 | let a = Item{value:7};
| - move occurs because `a` has type `Item`, which does not implement the `Copy` trait
9 | let b = a;
| - value moved here
10 | println!("value a {:?}, value b {:?}", a, b);
| ^ value borrowed here after move
|
note: if `Item` implemented `Clone`, you could clone the value
--> src/main.rs:3:1
|
3 | struct Item{
| ^^^^^^^^^^^ consider implementing `Clone` for this type
...
9 | let b = a;
| - you could clone this value
= note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)For more information about this error, try `rustc --explain E0382`.
报错的意思是变量a的所有权已经被移动到b，所以println！无法再使用a。
如果要想Item类的变量赋值后所有权继续有效，就需要Item类实现clone()。
方案一：手动为Item类实现trait Clone
#[derive(Debug)]
struct Item{value: i32,
}impl Clone for Item{fn clone(&self) -> Self{Item { value: self.value, }}
}fn main() {let a = Item{value:7};let b = a.clone();println!("value a {:?}, value b {:?}", a, b);
}编译运行：
Running `target\debug\greeting.exe`
value a Item { value: 7 }, value b Item { value: 7 }
方案二：
使用属性（Attribute）
#[derive(Debug, Clone)]
struct Item{value: i32,
}fn main() {let a = Item{value:7};let b = a.clone();println!("value a {:?}, value b {:?}", a, b);
}编译运行
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.01s
Running `target\debug\greeting.exe`
value a Item { value: 7 }, value b Item { value: 7 }
