ToOwned

为了解决 Clone trait 无法复制引用的值本身, 引入了 ToOwned trait. 它可以复制引用的真正的数据, 比如 &str 引用的 String, 只需要为 str 实现 ToOwned<Owned=String> 即可.

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

&str.to_owned()

将字符串切片转换成 String 对象:

#![allow(unused)]
fn main() {
let s: String = "hello".to_owned();
}

用到了 ToOwned trait:

use std::mem;

impl ToOwned for str {
    type Owned = String;
    #[inline]
    fn to_owned(&self) -> String {
        unsafe { String::from_utf8_unchecked(self.as_bytes().to_owned()) }
    }

    fn clone_into(&self, target: &mut String) {
        let mut b = mem::take(target).into_bytes();
        self.as_bytes().clone_into(&mut b);
        *target = unsafe { String::from_utf8_unchecked(b) }
    }
}

当然, 也可以这样写:

#![allow(unused)]
fn main() {
let s: String = "hello".to_string();
}

因为用到了 ToString trait:

impl ToString for str {
    #[inline]
    fn to_string(&self) -> String {
        String::from(self)
    }
}

相关信息

• Clone
• Cow