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//! 用于处理借用数据的模块。

#![stable(feature = "rust1", since = "1.0.0")]

use core::cmp::Ordering;
use core::hash::{Hash, Hasher};
use core::ops::Deref;
#[cfg(not(no_global_oom_handling))]
use core::ops::{Add, AddAssign};

#[stable(feature = "rust1", since = "1.0.0")]
pub use core::borrow::{Borrow, BorrowMut};

use crate::fmt;
#[cfg(not(no_global_oom_handling))]
use crate::string::String;

use Cow::*;

#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, B: ?Sized> Borrow<B> for Cow<'a, B>
where
    B: ToOwned,
    <B as ToOwned>::Owned: 'a,
{
    fn borrow(&self) -> &B {
        &**self
    }
}

/// `Clone` 对借用数据的泛化。
///
/// 某些类型通常可以通过实现 `Clone` trait 从借用变为拥有。
/// 但是 `Clone` 仅适用于从 `&T` 到 `T` 的情况。
/// `ToOwned` trait 泛化 `Clone` 来构造给定类型的任何借用数据。
///
#[cfg_attr(not(test), rustc_diagnostic_item = "ToOwned")]
#[stable(feature = "rust1", since = "1.0.0")]
pub trait ToOwned {
    /// 获得所有权后的结果类型。
    #[stable(feature = "rust1", since = "1.0.0")]
    type Owned: Borrow<Self>;

    /// 从借用的数据创建拥有的数据,通常是通过克隆。
    ///
    /// # Examples
    ///
    /// 基本用法:
    ///
    /// ```
    /// let s: &str = "a";
    /// let ss: String = s.to_owned();
    ///
    /// let v: &[i32] = &[1, 2];
    /// let vv: Vec<i32> = v.to_owned();
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use = "cloning is often expensive and is not expected to have side effects"]
    fn to_owned(&self) -> Self::Owned;

    /// 使用借来的数据来替换拥有的数据,通常是通过克隆。
    ///
    /// 这是 `Clone::clone_from` 的借用通用版本。
    ///
    /// # Examples
    ///
    /// 基本用法:
    ///
    /// ```
    /// # #![feature(toowned_clone_into)]
    /// let mut s: String = String::new();
    /// "hello".clone_into(&mut s);
    ///
    /// let mut v: Vec<i32> = Vec::new();
    /// [1, 2][..].clone_into(&mut v);
    /// ```
    #[unstable(feature = "toowned_clone_into", reason = "recently added", issue = "41263")]
    fn clone_into(&self, target: &mut Self::Owned) {
        *target = self.to_owned();
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T> ToOwned for T
where
    T: Clone,
{
    type Owned = T;
    fn to_owned(&self) -> T {
        self.clone()
    }

    fn clone_into(&self, target: &mut T) {
        target.clone_from(self);
    }
}

/// 写时克隆智能指针。
///
/// `Cow` 类型是一种智能指针,提供了写时克隆功能:它可以封装并提供对借用数据的不可变访问,并在需要可变的或所有权时懒惰地克隆数据。
///
/// 该类型旨在通过 `Borrow` trait 处理常规借用数据。
///
/// `Cow` 实现了 `Deref`,这意味着您可以直接在它包含的数据上调用非可变方法。
/// 如果需要进行可变的,则 `to_mut` 将获得一个拥有值的变量引用,必要时进行克隆。
///
/// 如果需要引用计数指针,请注意 [`Rc::make_mut`][crate::rc::Rc::make_mut] 和 [`Arc::make_mut`][crate::sync::Arc::make_mut] 也可以提供写时克隆功能。
///
/// # Examples
///
/// ```
/// use std::borrow::Cow;
///
/// fn abs_all(input: &mut Cow<[i32]>) {
///     for i in 0..input.len() {
///         let v = input[i];
///         if v < 0 {
///             // 如果尚未拥有,则克隆到 vector 中。
///             input.to_mut()[i] = -v;
///         }
///     }
/// }
///
/// // 因为 `input` 不需要可变的,所以不会发生克隆。
/// let slice = [0, 1, 2];
/// let mut input = Cow::from(&slice[..]);
/// abs_all(&mut input);
///
/// // 发生克隆是因为需要对 `input` 进行可变的。
/// let slice = [-1, 0, 1];
/// let mut input = Cow::from(&slice[..]);
/// abs_all(&mut input);
///
/// // 因为 `input` 已被拥有,所以不会发生克隆。
/// let mut input = Cow::from(vec![-1, 0, 1]);
/// abs_all(&mut input);
/// ```
///
/// 另一个示例显示如何将 `Cow` 保留在结构体中:
///
/// ```
/// use std::borrow::Cow;
///
/// struct Items<'a, X: 'a> where [X]: ToOwned<Owned = Vec<X>> {
///     values: Cow<'a, [X]>,
/// }
///
/// impl<'a, X: Clone + 'a> Items<'a, X> where [X]: ToOwned<Owned = Vec<X>> {
///     fn new(v: Cow<'a, [X]>) -> Self {
///         Items { values: v }
///     }
/// }
///
/// // 根据切片的借用值创建容器
/// let readonly = [1, 2];
/// let borrowed = Items::new((&readonly[..]).into());
/// match borrowed {
///     Items { values: Cow::Borrowed(b) } => println!("borrowed {:?}", b),
///     _ => panic!("expect borrowed value"),
/// }
///
/// let mut clone_on_write = borrowed;
/// // 将切片中的数据可变的为拥有的 vec,并在顶部推入新值
/// clone_on_write.values.to_mut().push(3);
/// println!("clone_on_write = {:?}", clone_on_write.values);
///
/// // 数据被可变的。让我们检查一下。
/// match clone_on_write {
///     Items { values: Cow::Owned(_) } => println!("clone_on_write contains owned data"),
///     _ => panic!("expect owned data"),
/// }
/// ```
///
///
///
///
///
///
#[stable(feature = "rust1", since = "1.0.0")]
#[cfg_attr(not(test), rustc_diagnostic_item = "Cow")]
pub enum Cow<'a, B: ?Sized + 'a>
where
    B: ToOwned,
{
    /// 借用的数据。
    #[stable(feature = "rust1", since = "1.0.0")]
    Borrowed(#[stable(feature = "rust1", since = "1.0.0")] &'a B),

    /// 拥有的数据。
    #[stable(feature = "rust1", since = "1.0.0")]
    Owned(#[stable(feature = "rust1", since = "1.0.0")] <B as ToOwned>::Owned),
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<B: ?Sized + ToOwned> Clone for Cow<'_, B> {
    fn clone(&self) -> Self {
        match *self {
            Borrowed(b) => Borrowed(b),
            Owned(ref o) => {
                let b: &B = o.borrow();
                Owned(b.to_owned())
            }
        }
    }

    fn clone_from(&mut self, source: &Self) {
        match (self, source) {
            (&mut Owned(ref mut dest), &Owned(ref o)) => o.borrow().clone_into(dest),
            (t, s) => *t = s.clone(),
        }
    }
}

impl<B: ?Sized + ToOwned> Cow<'_, B> {
    /// 如果借用了数据 (即 `to_mut` 需要其他工作),则返回 true。
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(cow_is_borrowed)]
    /// use std::borrow::Cow;
    ///
    /// let cow = Cow::Borrowed("moo");
    /// assert!(cow.is_borrowed());
    ///
    /// let bull: Cow<'_, str> = Cow::Owned("...moo?".to_string());
    /// assert!(!bull.is_borrowed());
    /// ```
    #[unstable(feature = "cow_is_borrowed", issue = "65143")]
    #[rustc_const_unstable(feature = "const_cow_is_borrowed", issue = "65143")]
    pub const fn is_borrowed(&self) -> bool {
        match *self {
            Borrowed(_) => true,
            Owned(_) => false,
        }
    }

    /// 如果数据已拥有,即 `to_mut` 为无操作,则返回 true。
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(cow_is_borrowed)]
    /// use std::borrow::Cow;
    ///
    /// let cow: Cow<'_, str> = Cow::Owned("moo".to_string());
    /// assert!(cow.is_owned());
    ///
    /// let bull = Cow::Borrowed("...moo?");
    /// assert!(!bull.is_owned());
    /// ```
    #[unstable(feature = "cow_is_borrowed", issue = "65143")]
    #[rustc_const_unstable(feature = "const_cow_is_borrowed", issue = "65143")]
    pub const fn is_owned(&self) -> bool {
        !self.is_borrowed()
    }

    /// 获取对数据拥有形式的可变引用。
    ///
    /// 如果数据尚未拥有,则克隆数据
    ///
    /// # Examples
    ///
    /// ```
    /// use std::borrow::Cow;
    ///
    /// let mut cow = Cow::Borrowed("foo");
    /// cow.to_mut().make_ascii_uppercase();
    ///
    /// assert_eq!(
    ///   cow,
    ///   Cow::Owned(String::from("FOO")) as Cow<str>
    /// );
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn to_mut(&mut self) -> &mut <B as ToOwned>::Owned {
        match *self {
            Borrowed(borrowed) => {
                *self = Owned(borrowed.to_owned());
                match *self {
                    Borrowed(..) => unreachable!(),
                    Owned(ref mut owned) => owned,
                }
            }
            Owned(ref mut owned) => owned,
        }
    }

    /// 提取拥有的数据。
    ///
    /// 如果数据尚未拥有,则克隆数据
    ///
    /// # Examples
    ///
    /// 在 `Cow::Borrowed` 上调用 `into_owned` 会克隆底层数据并成为 `Cow::Owned`:
    ///
    ///
    /// ```
    /// use std::borrow::Cow;
    ///
    /// let s = "Hello world!";
    /// let cow = Cow::Borrowed(s);
    ///
    /// assert_eq!(
    ///   cow.into_owned(),
    ///   String::from(s)
    /// );
    /// ```
    ///
    /// 禁止在 `Cow::Owned` 上调用 `into_owned`:
    ///
    /// ```
    /// use std::borrow::Cow;
    ///
    /// let s = "Hello world!";
    /// let cow: Cow<str> = Cow::Owned(String::from(s));
    ///
    /// assert_eq!(
    ///   cow.into_owned(),
    ///   String::from(s)
    /// );
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn into_owned(self) -> <B as ToOwned>::Owned {
        match self {
            Borrowed(borrowed) => borrowed.to_owned(),
            Owned(owned) => owned,
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_deref", issue = "88955")]
impl<B: ?Sized + ToOwned> const Deref for Cow<'_, B>
where
    B::Owned: ~const Borrow<B>,
{
    type Target = B;

    fn deref(&self) -> &B {
        match *self {
            Borrowed(borrowed) => borrowed,
            Owned(ref owned) => owned.borrow(),
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<B: ?Sized> Eq for Cow<'_, B> where B: Eq + ToOwned {}

#[stable(feature = "rust1", since = "1.0.0")]
impl<B: ?Sized> Ord for Cow<'_, B>
where
    B: Ord + ToOwned,
{
    #[inline]
    fn cmp(&self, other: &Self) -> Ordering {
        Ord::cmp(&**self, &**other)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, 'b, B: ?Sized, C: ?Sized> PartialEq<Cow<'b, C>> for Cow<'a, B>
where
    B: PartialEq<C> + ToOwned,
    C: ToOwned,
{
    #[inline]
    fn eq(&self, other: &Cow<'b, C>) -> bool {
        PartialEq::eq(&**self, &**other)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, B: ?Sized> PartialOrd for Cow<'a, B>
where
    B: PartialOrd + ToOwned,
{
    #[inline]
    fn partial_cmp(&self, other: &Cow<'a, B>) -> Option<Ordering> {
        PartialOrd::partial_cmp(&**self, &**other)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<B: ?Sized> fmt::Debug for Cow<'_, B>
where
    B: fmt::Debug + ToOwned<Owned: fmt::Debug>,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            Borrowed(ref b) => fmt::Debug::fmt(b, f),
            Owned(ref o) => fmt::Debug::fmt(o, f),
        }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<B: ?Sized> fmt::Display for Cow<'_, B>
where
    B: fmt::Display + ToOwned<Owned: fmt::Display>,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            Borrowed(ref b) => fmt::Display::fmt(b, f),
            Owned(ref o) => fmt::Display::fmt(o, f),
        }
    }
}

#[stable(feature = "default", since = "1.11.0")]
impl<B: ?Sized> Default for Cow<'_, B>
where
    B: ToOwned<Owned: Default>,
{
    /// 使用包含的拥有值的默认值创建一个拥有的 Cow<'a, B>。
    fn default() -> Self {
        Owned(<B as ToOwned>::Owned::default())
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<B: ?Sized> Hash for Cow<'_, B>
where
    B: Hash + ToOwned,
{
    #[inline]
    fn hash<H: Hasher>(&self, state: &mut H) {
        Hash::hash(&**self, state)
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + ToOwned> AsRef<T> for Cow<'_, T> {
    fn as_ref(&self) -> &T {
        self
    }
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "cow_add", since = "1.14.0")]
impl<'a> Add<&'a str> for Cow<'a, str> {
    type Output = Cow<'a, str>;

    #[inline]
    fn add(mut self, rhs: &'a str) -> Self::Output {
        self += rhs;
        self
    }
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "cow_add", since = "1.14.0")]
impl<'a> Add<Cow<'a, str>> for Cow<'a, str> {
    type Output = Cow<'a, str>;

    #[inline]
    fn add(mut self, rhs: Cow<'a, str>) -> Self::Output {
        self += rhs;
        self
    }
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "cow_add", since = "1.14.0")]
impl<'a> AddAssign<&'a str> for Cow<'a, str> {
    fn add_assign(&mut self, rhs: &'a str) {
        if self.is_empty() {
            *self = Cow::Borrowed(rhs)
        } else if !rhs.is_empty() {
            if let Cow::Borrowed(lhs) = *self {
                let mut s = String::with_capacity(lhs.len() + rhs.len());
                s.push_str(lhs);
                *self = Cow::Owned(s);
            }
            self.to_mut().push_str(rhs);
        }
    }
}

#[cfg(not(no_global_oom_handling))]
#[stable(feature = "cow_add", since = "1.14.0")]
impl<'a> AddAssign<Cow<'a, str>> for Cow<'a, str> {
    fn add_assign(&mut self, rhs: Cow<'a, str>) {
        if self.is_empty() {
            *self = rhs
        } else if !rhs.is_empty() {
            if let Cow::Borrowed(lhs) = *self {
                let mut s = String::with_capacity(lhs.len() + rhs.len());
                s.push_str(lhs);
                *self = Cow::Owned(s);
            }
            self.to_mut().push_str(&rhs);
        }
    }
}