Trait core::clone::Clone

1.0.0 · source ·

pub trait Clone: Sized {
    // Required method
    fn clone(&self) -> Self;

    // Provided method
    fn clone_from(&mut self, source: &Self) { ... }
}

Expand description

通用的 trait，用于显式复制对象。

与 Copy 的不同之处在于 Copy 是隐式的并且是廉价的按位复制，而 Clone 始终是显式的并且可能昂贵也可能不昂贵。为了强制执行这些特性，Rust 不允许您重新实现 Copy，但是您可以重新实现 Clone 并运行任意代码。

由于 Clone 比 Copy 更通用，因此您可以自动将 Copy 设为 Clone。

Derivable

如果所有字段均为 Clone，则此 trait 可以与 #[derive] 一起使用。Clone 的 derived 实现在每个字段上调用 clone。

对于泛型结构体，#[derive] 通过在泛型参数上添加绑定的 Clone 有条件地实现 Clone。

// 当 T 是 Clone 时，`derive` 为 Reading<T> 实现了 Clone。
#[derive(Clone)]
struct Reading<T> {
    frequency: T,
}

Run

如何实现 `Clone`？

Copy 类型应该实现 Clone 的简单实现。更正式地：如果 T: Copy，x: T 和 y: &T，则 let x = y.clone(); 等效于 let x = *y;。手动执行时应注意保持不变。但是，不安全的代码一定不能依靠它来确保内存安全。

一个示例是持有函数指针的泛型结构体。在这种情况下，不能对 Clone 的实现进行派生操作，而可以将其实现为：

struct Generate<T>(fn() -> T);

impl<T> Copy for Generate<T> {}

impl<T> Clone for Generate<T> {
    fn clone(&self) -> Self {
        *self
    }
}

Run

其他实现者

除了下面列出的实现者外，以下类型还实现了 Clone：

函数项类型 (即，为每个函数定义的不同类型)
函数指针类型 (例如 fn() -> i32)
闭包类型，如果它们没有从环境中捕获任何值，或者所有此类捕获的值本身都实现了 Clone。请注意，由共享引用捕获的变量始终实现 Clone (即使引用对象没有实现)，而由变量引用捕获的变量从不实现 Clone。

Required Methods§

source

fn clone(&self) -> Self

返回值的副本。

Examples

let hello = "Hello"; // &str 实现克隆

assert_eq!("Hello", hello.clone());

Run

Provided Methods§

source

fn clone_from(&mut self, source: &Self)

从 source 执行复制分配。

a.clone_from(&b) 在功能上等同于 a = b.clone()，但可以被覆盖以重用 a 的资源以避免不必要的分配。

Trait core::clone::Clone

Required Methods§

fn clone(&self) -> Self

Provided Methods§

fn clone_from(&mut self, source: &Self)

Implementors§

impl Clone for AsciiChar

impl Clone for core::cmp::Ordering

impl Clone for Infallible

impl Clone for core::fmt::Alignment

impl Clone for IpAddr

impl Clone for Ipv6MulticastScope

impl Clone for SocketAddr

impl Clone for FpCategory

impl Clone for IntErrorKind

impl Clone for Which

impl Clone for SearchStep

impl Clone for core::sync::atomic::Ordering

impl Clone for bool

impl Clone for char

impl Clone for f32

impl Clone for f64

impl Clone for i8

impl Clone for i16

impl Clone for i32

impl Clone for i64

impl Clone for i128

impl Clone for isize

impl Clone for !

impl Clone for u8

impl Clone for u16

impl Clone for u32

impl Clone for u64

impl Clone for u128

impl Clone for ()

impl Clone for usize

impl Clone for AllocError

impl Clone for Layout

impl Clone for LayoutError

impl Clone for TypeId

impl Clone for float64x1_t

impl Clone for float64x1x2_t

impl Clone for float64x1x3_t

impl Clone for float64x1x4_t

impl Clone for float64x2_t

impl Clone for float64x2x2_t

impl Clone for float64x2x3_t

impl Clone for float64x2x4_t

impl Clone for int16x2_t

impl Clone for uint16x2_t

impl Clone for float32x2_t

impl Clone for float32x2x2_t

impl Clone for float32x2x3_t

impl Clone for float32x2x4_t

impl Clone for float32x4_t

impl Clone for float32x4x2_t

impl Clone for float32x4x3_t

impl Clone for float32x4x4_t

impl Clone for int8x4_t

impl Clone for int8x8_t

impl Clone for int8x8x2_t

impl Clone for int8x8x3_t

impl Clone for int8x8x4_t

impl Clone for int8x16_t

impl Clone for int8x16x2_t

impl Clone for int8x16x3_t

impl Clone for int8x16x4_t

impl Clone for int16x4_t

impl Clone for int16x4x2_t

impl Clone for int16x4x3_t

impl Clone for int16x4x4_t

impl Clone for int16x8_t

impl Clone for int16x8x2_t

impl Clone for int16x8x3_t

impl Clone for int16x8x4_t

impl Clone for int32x2_t

impl Clone for int32x2x2_t

impl Clone for int32x2x3_t

impl Clone for int32x2x4_t

impl Clone for int32x4_t