Rust 笔记 - ToOwned trait

在Rust中，一般通过clone 方法来获取变量的副本。但有的类型，如&str 或 &[u8]等无法通过实现Clone trait 来实现 clone方法。于是便有了ToOwned trait。下面看一下定义：

trait ToOwned {
    type Owned: Borrow<Self>;
    fn to_owned(&self) -> Self::Owned;
}

下面是实现例子：

use std::borrow::Borrow;

#[derive(Debug)]
struct Any<'a, T> {
    content: &'a T,
}

#[derive(Debug)]
struct One<'a, T> {
    any: Any<'a, T>,
}

impl<'a, T> std::borrow::Borrow<Any<'a, T>> for One<'a, T> {
    fn borrow(&self) -> &Any<'a, T> {
        &self.any
    }
}

impl<'a, T> std::borrow::ToOwned for Any<'a, T> {
    type Owned = One<'a, T>;
    fn to_owned(&self) -> Self::Owned {
        One {
            any: Any {
                content: self.content.clone(),
            },
        }
    }
}

fn main() {
    let content = "hello".to_owned();
    let o = One { any: Any { content: &content },};
    let b: &Any<String> = o.borrow();
    println!("{:?}", b); // Any { content: "hello" }

    let a = Any { content: &content };
    let b = a.to_owned();
    println!("{:?}", b); // One { any: Any { content: "hello" } }
}