use crate::fmt;
use crate::hash::Hash;

/// 无限制范围 (`..`)。
///
/// `RangeFull` 主要用作 [slicing index]，其简写为 `..`。
/// 它不能用作 [`Iterator`]，因为它没有起点。
///
/// # Examples
///
/// `..` 语法是 `RangeFull`:
///
/// ```
/// assert_eq!((..), std::ops::RangeFull);
/// ```
///
/// 它没有 [`IntoIterator`] 实现，因此不能直接在 `for` 循环中使用它。
/// 这不会编译:
///
/// ```compile_fail,E0277
/// for i in .. {
///     // ...
/// }
/// ```
///
/// 用作 [slicing index] 时，`RangeFull` 产生完整的阵列作为切片。
///
/// ```
/// let arr = [0, 1, 2, 3, 4];
/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]); // 这是 `RangeFull`
/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
/// assert_eq!(arr[1.. 3], [   1, 2      ]);
/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
/// ```
///
/// [slicing index]: crate::slice::SliceIndex
#[lang = "RangeFull"]
#[doc(alias = "..")]
#[derive(Copy, Clone, Default, PartialEq, Eq, Hash)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct RangeFull;

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Debug for RangeFull {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(fmt, "..")
    }
}

/// (half-open) 范围包括在 (`start..end`) 之下和仅在 (`start..end`) 之上。
///
///
/// 范围 `start..end` 包含 `start <= x < end` 的所有值。
/// 如果为 `start >= end`，则为空。
///
/// # Examples
///
/// `start..end` 语法是 `Range`:
///
/// ```
/// assert_eq!((3..5), std::ops::Range { start: 3, end: 5 });
/// assert_eq!(3 + 4 + 5, (3..6).sum());
/// ```
///
/// ```
/// let arr = [0, 1, 2, 3, 4];
/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
/// assert_eq!(arr[1.. 3], [   1, 2      ]); // 这是 `Range`
/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
/// ```
#[lang = "Range"]
#[doc(alias = "..")]
#[derive(Clone, Default, PartialEq, Eq, Hash)] // 没有 Copy - 请参见 #27186
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Range<Idx> {
    /// (inclusive) 范围的下限。
    #[stable(feature = "rust1", since = "1.0.0")]
    pub start: Idx,
    /// 范围 (exclusive) 的上限。
    #[stable(feature = "rust1", since = "1.0.0")]
    pub end: Idx,
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<Idx: fmt::Debug> fmt::Debug for Range<Idx> {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.start.fmt(fmt)?;
        write!(fmt, "..")?;
        self.end.fmt(fmt)?;
        Ok(())
    }
}

impl<Idx: PartialOrd<Idx>> Range<Idx> {
    /// 如果范围中包含 `item`，则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!(!(3..5).contains(&2));
    /// assert!( (3..5).contains(&3));
    /// assert!( (3..5).contains(&4));
    /// assert!(!(3..5).contains(&5));
    ///
    /// assert!(!(3..3).contains(&3));
    /// assert!(!(3..2).contains(&3));
    ///
    /// assert!( (0.0..1.0).contains(&0.5));
    /// assert!(!(0.0..1.0).contains(&f32::NAN));
    /// assert!(!(0.0..f32::NAN).contains(&0.5));
    /// assert!(!(f32::NAN..1.0).contains(&0.5));
    /// ```
    #[stable(feature = "range_contains", since = "1.35.0")]
    pub fn contains<U>(&self, item: &U) -> bool
    where
        Idx: PartialOrd<U>,
        U: ?Sized + PartialOrd<Idx>,
    {
        <Self as RangeBounds<Idx>>::contains(self, item)
    }

    /// 如果范围不包含任何项，则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!(!(3..5).is_empty());
    /// assert!( (3..3).is_empty());
    /// assert!( (3..2).is_empty());
    /// ```
    ///
    /// 如果任何一方都无法比拟，则范围为空:
    ///
    /// ```
    /// assert!(!(3.0..5.0).is_empty());
    /// assert!( (3.0..f32::NAN).is_empty());
    /// assert!( (f32::NAN..5.0).is_empty());
    /// ```
    #[stable(feature = "range_is_empty", since = "1.47.0")]
    pub fn is_empty(&self) -> bool {
        !(self.start < self.end)
    }
}

/// 范围仅包括 (`start..`) 以下的范围。
///
/// `RangeFrom` `start..` 包含 `x >= start` 的所有值。
///
/// *Note*: [`Iterator`] 实现中的溢出 (当所包含的数据类型达到其数值限制时) 允许 panic，自动换行或饱和。
/// 此行为由 [`Step`] trait 的实现定义。
/// 对于原始整数，这遵循正常规则，并遵守溢出检查配置文件 (调试中为 panic，释放中为包装)。
/// 还要注意，溢出发生的时间比您想像的要早: 溢出发生在 `next` 的调用中，该调用会产生最大值，因为必须将范围设置为产生下一个值的状态。
///
///
/// [`Step`]: crate::iter::Step
///
/// # Examples
///
/// `start..` 语法是 `RangeFrom`:
///
/// ```
/// assert_eq!((2..), std::ops::RangeFrom { start: 2 });
/// assert_eq!(2 + 3 + 4, (2..).take(3).sum());
/// ```
///
/// ```
/// let arr = [0, 1, 2, 3, 4];
/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]); // 这是 `RangeFrom`
/// assert_eq!(arr[1.. 3], [   1, 2      ]);
/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
/// ```
///
///
///
#[lang = "RangeFrom"]
#[doc(alias = "..")]
#[derive(Clone, PartialEq, Eq, Hash)] // 没有 Copy - 请参见 #27186
#[stable(feature = "rust1", since = "1.0.0")]
pub struct RangeFrom<Idx> {
    /// (inclusive) 范围的下限。
    #[stable(feature = "rust1", since = "1.0.0")]
    pub start: Idx,
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<Idx: fmt::Debug> fmt::Debug for RangeFrom<Idx> {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.start.fmt(fmt)?;
        write!(fmt, "..")?;
        Ok(())
    }
}

impl<Idx: PartialOrd<Idx>> RangeFrom<Idx> {
    /// 如果范围中包含 `item`，则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!(!(3..).contains(&2));
    /// assert!( (3..).contains(&3));
    /// assert!( (3..).contains(&1_000_000_000));
    ///
    /// assert!( (0.0..).contains(&0.5));
    /// assert!(!(0.0..).contains(&f32::NAN));
    /// assert!(!(f32::NAN..).contains(&0.5));
    /// ```
    #[stable(feature = "range_contains", since = "1.35.0")]
    pub fn contains<U>(&self, item: &U) -> bool
    where
        Idx: PartialOrd<U>,
        U: ?Sized + PartialOrd<Idx>,
    {
        <Self as RangeBounds<Idx>>::contains(self, item)
    }
}

/// 范围仅排在 (`..end`) 之上。
///
/// `RangeTo` `..end` 包含 `x < end` 的所有值。
/// 它不能用作 [`Iterator`]，因为它没有起点。
///
/// # Examples
///
/// `..end` 语法是 `RangeTo`:
///
/// ```
/// assert_eq!((..5), std::ops::RangeTo { end: 5 });
/// ```
///
/// 它没有 [`IntoIterator`] 实现，因此不能直接在 `for` 循环中使用它。
/// 这不会编译:
///
/// ```compile_fail,E0277
/// // 错误 [E0277]: trait bound`std::RangeTo <{integer}>:
/// // std::Iterator` 不满足
/// for i in ..5 {
///     // ...
/// }
/// ```
///
/// 当用作 [slicing index] 时，`RangeTo` 会在 `end` 所指示的索引之前生成所有数组元素的切片。
///
///
/// ```
/// let arr = [0, 1, 2, 3, 4];
/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
/// assert_eq!(arr[ .. 3], [0, 1, 2      ]); // 这是 `RangeTo`
/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
/// assert_eq!(arr[1.. 3], [   1, 2      ]);
/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
/// ```
///
/// [slicing index]: crate::slice::SliceIndex
#[lang = "RangeTo"]
#[doc(alias = "..")]
#[derive(Copy, Clone, PartialEq, Eq, Hash)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct RangeTo<Idx> {
    /// 范围 (exclusive) 的上限。
    #[stable(feature = "rust1", since = "1.0.0")]
    pub end: Idx,
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<Idx: fmt::Debug> fmt::Debug for RangeTo<Idx> {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(fmt, "..")?;
        self.end.fmt(fmt)?;
        Ok(())
    }
}

impl<Idx: PartialOrd<Idx>> RangeTo<Idx> {
    /// 如果范围中包含 `item`，则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!( (..5).contains(&-1_000_000_000));
    /// assert!( (..5).contains(&4));
    /// assert!(!(..5).contains(&5));
    ///
    /// assert!( (..1.0).contains(&0.5));
    /// assert!(!(..1.0).contains(&f32::NAN));
    /// assert!(!(..f32::NAN).contains(&0.5));
    /// ```
    #[stable(feature = "range_contains", since = "1.35.0")]
    pub fn contains<U>(&self, item: &U) -> bool
    where
        Idx: PartialOrd<U>,
        U: ?Sized + PartialOrd<Idx>,
    {
        <Self as RangeBounds<Idx>>::contains(self, item)
    }
}

/// 范围包括 (`start..=end`) 的上下边界。
///
/// `RangeInclusive` `start..=end` 包含 `x >= start` 和 `x <= end` 的所有值。除非 `start <= end`，否则为空。
///
/// 这个迭代器是 [fused]，但是迭代完成后 `start` 和 `end` 的特定值是未指定的，除了 [`.is_empty()`]之外，一旦不再产生值，就会返回 `true`。
///
///
/// [fused]: crate::iter::FusedIterator
/// [`.is_empty()`]: RangeInclusive::is_empty
///
/// # Examples
///
/// `start..=end` 语法是 `RangeInclusive`:
///
/// ```
/// assert_eq!((3..=5), std::ops::RangeInclusive::new(3, 5));
/// assert_eq!(3 + 4 + 5, (3..=5).sum());
/// ```
///
/// ```
/// let arr = [0, 1, 2, 3, 4];
/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
/// assert_eq!(arr[1.. 3], [   1, 2      ]);
/// assert_eq!(arr[1..=3], [   1, 2, 3   ]); // 这是 `RangeInclusive`
/// ```
///
///
#[lang = "RangeInclusive"]
#[doc(alias = "..=")]
#[derive(Clone, PartialEq, Eq, Hash)] // 没有 Copy - 请参见 #27186
#[stable(feature = "inclusive_range", since = "1.26.0")]
pub struct RangeInclusive<Idx> {
    // 请注意，此处的字段不是公开的，以允许更改 future 中的表示形式。尤其是，尽管我们可能公开 start/end，但在不更改 (future/current) 私有字段的情况下对其进行修改可能会导致错误的行为，因此我们不希望支持该模式。
    //
    //
    //
    //
    pub(crate) start: Idx,
    pub(crate) end: Idx,

    // 该字段是:
    //  - `false` 创建时
    //  - `false` 当迭代产生一个元素并且迭代器没有耗尽时
    //  - `true` 当迭代已用于耗尽迭代器时
    //
    // 这是支持 PartialEq 和 Hash 而没有 PartialOrd 绑定或特殊化所必需的。
    pub(crate) exhausted: bool,
}

impl<Idx> RangeInclusive<Idx> {
    /// 创建一个新的包含范围。等同于编写 `start..=end`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::ops::RangeInclusive;
    ///
    /// assert_eq!(3..=5, RangeInclusive::new(3, 5));
    /// ```
    #[lang = "range_inclusive_new"]
    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
    #[inline]
    #[rustc_promotable]
    #[rustc_const_stable(feature = "const_range_new", since = "1.32.0")]
    pub const fn new(start: Idx, end: Idx) -> Self {
        Self { start, end, exhausted: false }
    }

    /// 返回范围 (inclusive) 的下限。
    ///
    /// 当使用包含范围进行迭代时，在迭代结束后未指定 `start()` 和 [`end()`] 的值。
    /// 若要确定包含范围是否为空，请使用 [`is_empty()`] 方法而不是比较 `start() > end()`。
    ///
    /// Note: 范围迭代到穷竭之后，此方法返回的值是不确定的。
    ///
    /// [`end()`]: RangeInclusive::end
    /// [`is_empty()`]: RangeInclusive::is_empty
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!((3..=5).start(), &3);
    /// ```
    ///
    ///
    ///
    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
    #[rustc_const_stable(feature = "const_inclusive_range_methods", since = "1.32.0")]
    #[inline]
    pub const fn start(&self) -> &Idx {
        &self.start
    }

    /// 返回范围 (inclusive) 的上限。
    ///
    /// 当使用包含范围进行迭代时，在迭代结束后未指定 [`start()`] 和 `end()` 的值。
    /// 若要确定包含范围是否为空，请使用 [`is_empty()`] 方法而不是比较 `start() > end()`。
    ///
    /// Note: 范围迭代到穷竭之后，此方法返回的值是不确定的。
    ///
    /// [`start()`]: RangeInclusive::start
    /// [`is_empty()`]: RangeInclusive::is_empty
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!((3..=5).end(), &5);
    /// ```
    ///
    ///
    ///
    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
    #[rustc_const_stable(feature = "const_inclusive_range_methods", since = "1.32.0")]
    #[inline]
    pub const fn end(&self) -> &Idx {
        &self.end
    }

    /// 将 `RangeInclusive` 分解为 (下限 (inclusive) 上限)。
    ///
    /// Note: 范围迭代到穷竭之后，此方法返回的值是不确定的。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!((3..=5).into_inner(), (3, 5));
    /// ```
    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
    #[inline]
    pub fn into_inner(self) -> (Idx, Idx) {
        (self.start, self.end)
    }
}

impl RangeInclusive<usize> {
    /// 转换为 `SliceIndex` 实现的专用 `Range`。
    /// 调用者负责处理 `end == usize::MAX`。
    #[inline]
    pub(crate) fn into_slice_range(self) -> Range<usize> {
        // 如果我们不筋疲力尽，我们只想切片 `start..end + 1`。
        // 如果我们筋疲力尽，则使用 `end + 1..end + 1` 切片会为我们提供一个空范围，该范围仍受该端点的边界检查的影响。
        //
        let exclusive_end = self.end + 1;
        let start = if self.exhausted { exclusive_end } else { self.start };
        start..exclusive_end
    }
}

#[stable(feature = "inclusive_range", since = "1.26.0")]
impl<Idx: fmt::Debug> fmt::Debug for RangeInclusive<Idx> {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.start.fmt(fmt)?;
        write!(fmt, "..=")?;
        self.end.fmt(fmt)?;
        if self.exhausted {
            write!(fmt, " (exhausted)")?;
        }
        Ok(())
    }
}

impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
    /// 如果范围中包含 `item`，则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!(!(3..=5).contains(&2));
    /// assert!( (3..=5).contains(&3));
    /// assert!( (3..=5).contains(&4));
    /// assert!( (3..=5).contains(&5));
    /// assert!(!(3..=5).contains(&6));
    ///
    /// assert!( (3..=3).contains(&3));
    /// assert!(!(3..=2).contains(&3));
    ///
    /// assert!( (0.0..=1.0).contains(&1.0));
    /// assert!(!(0.0..=1.0).contains(&f32::NAN));
    /// assert!(!(0.0..=f32::NAN).contains(&0.0));
    /// assert!(!(f32::NAN..=1.0).contains(&1.0));
    /// ```
    ///
    /// 迭代完成后，此方法总是返回 `false`:
    ///
    /// ```
    /// let mut r = 3..=5;
    /// assert!(r.contains(&3) && r.contains(&5));
    /// for _ in r.by_ref() {}
    /// // 此处未指定精确的字段值
    /// assert!(!r.contains(&3) && !r.contains(&5));
    /// ```
    #[stable(feature = "range_contains", since = "1.35.0")]
    pub fn contains<U>(&self, item: &U) -> bool
    where
        Idx: PartialOrd<U>,
        U: ?Sized + PartialOrd<Idx>,
    {
        <Self as RangeBounds<Idx>>::contains(self, item)
    }

    /// 如果范围不包含任何项，则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!(!(3..=5).is_empty());
    /// assert!(!(3..=3).is_empty());
    /// assert!( (3..=2).is_empty());
    /// ```
    ///
    /// 如果任何一方都无法比拟，则范围为空:
    ///
    /// ```
    /// assert!(!(3.0..=5.0).is_empty());
    /// assert!( (3.0..=f32::NAN).is_empty());
    /// assert!( (f32::NAN..=5.0).is_empty());
    /// ```
    ///
    /// 迭代完成后，此方法返回 `true`:
    ///
    /// ```
    /// let mut r = 3..=5;
    /// for _ in r.by_ref() {}
    /// // 此处未指定精确的字段值
    /// assert!(r.is_empty());
    /// ```
    #[stable(feature = "range_is_empty", since = "1.47.0")]
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.exhausted || !(self.start <= self.end)
    }
}

/// 范围仅包括 (`..=end`) 以上的范围。
///
/// `RangeToInclusive` `..=end` 包含 `x <= end` 的所有值。
/// 它不能用作 [`Iterator`]，因为它没有起点。
///
/// # Examples
///
/// `..=end` 语法是 `RangeToInclusive`:
///
/// ```
/// assert_eq!((..=5), std::ops::RangeToInclusive{ end: 5 });
/// ```
///
/// 它没有 [`IntoIterator`] 实现，因此不能直接在 `for` 循环中使用它。这不会编译:
///
/// ```compile_fail,E0277
/// // 错误 [E0277]: trait bound`std::RangeToInclusive <{integer}>:
/// // std::Iterator` 不满足
/// for i in ..=5 {
///     // ...
/// }
/// ```
///
/// 当用作 [slicing index] 时，`RangeToInclusive` 会生成所有数组元素的切片，直到并包括 `end` 指示的索引。
///
///
/// ```
/// let arr = [0, 1, 2, 3, 4];
/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]); // 这是 `RangeToInclusive`
/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
/// assert_eq!(arr[1.. 3], [   1, 2      ]);
/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
/// ```
///
/// [slicing index]: crate::slice::SliceIndex
///
#[lang = "RangeToInclusive"]
#[doc(alias = "..=")]
#[derive(Copy, Clone, PartialEq, Eq, Hash)]
#[stable(feature = "inclusive_range", since = "1.26.0")]
pub struct RangeToInclusive<Idx> {
    /// 范围 (inclusive) 的上限
    #[stable(feature = "inclusive_range", since = "1.26.0")]
    pub end: Idx,
}

#[stable(feature = "inclusive_range", since = "1.26.0")]
impl<Idx: fmt::Debug> fmt::Debug for RangeToInclusive<Idx> {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(fmt, "..=")?;
        self.end.fmt(fmt)?;
        Ok(())
    }
}

impl<Idx: PartialOrd<Idx>> RangeToInclusive<Idx> {
    /// 如果范围中包含 `item`，则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!( (..=5).contains(&-1_000_000_000));
    /// assert!( (..=5).contains(&5));
    /// assert!(!(..=5).contains(&6));
    ///
    /// assert!( (..=1.0).contains(&1.0));
    /// assert!(!(..=1.0).contains(&f32::NAN));
    /// assert!(!(..=f32::NAN).contains(&0.5));
    /// ```
    #[stable(feature = "range_contains", since = "1.35.0")]
    pub fn contains<U>(&self, item: &U) -> bool
    where
        Idx: PartialOrd<U>,
        U: ?Sized + PartialOrd<Idx>,
    {
        <Self as RangeBounds<Idx>>::contains(self, item)
    }
}

// RangeToInclusive<Idx> 无法暗示 From<RangeTo<Idx>>，因为 (..0) .into () 可能会发生下溢
//

/// 一系列键的端点。
///
/// # Examples
///
/// 边界是范围端点:
///
/// ```
/// use std::ops::Bound::*;
/// use std::ops::RangeBounds;
///
/// assert_eq!((..100).start_bound(), Unbounded);
/// assert_eq!((1..12).start_bound(), Included(&1));
/// assert_eq!((1..12).end_bound(), Excluded(&12));
/// ```
///
/// 使用 `Bound`s 的元组作为 [`BTreeMap::range`] 的参数。
/// 请注意，在大多数情况下，最好改用范围语法 (`1..5`)。
///
/// ```
/// use std::collections::BTreeMap;
/// use std::ops::Bound::{Excluded, Included, Unbounded};
///
/// let mut map = BTreeMap::new();
/// map.insert(3, "a");
/// map.insert(5, "b");
/// map.insert(8, "c");
///
/// for (key, value) in map.range((Excluded(3), Included(8))) {
///     println!("{}: {}", key, value);
/// }
///
/// assert_eq!(Some((&3, &"a")), map.range((Unbounded, Included(5))).next());
/// ```
///
/// [`BTreeMap::range`]: ../../std/collections/btree_map/struct.BTreeMap.html#method.range
#[stable(feature = "collections_bound", since = "1.17.0")]
#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
pub enum Bound<T> {
    /// 包容性范围。
    #[stable(feature = "collections_bound", since = "1.17.0")]
    Included(#[stable(feature = "collections_bound", since = "1.17.0")] T),
    /// 排他性约束。
    #[stable(feature = "collections_bound", since = "1.17.0")]
    Excluded(#[stable(feature = "collections_bound", since = "1.17.0")] T),
    /// 无限端点。指示此方向没有界限。
    #[stable(feature = "collections_bound", since = "1.17.0")]
    Unbounded,
}

impl<T> Bound<T> {
    /// 从 `&Bound<T>` 转换为 `Bound<&T>`。
    #[inline]
    #[unstable(feature = "bound_as_ref", issue = "80996")]
    pub fn as_ref(&self) -> Bound<&T> {
        match *self {
            Included(ref x) => Included(x),
            Excluded(ref x) => Excluded(x),
            Unbounded => Unbounded,
        }
    }

    /// 从 `&mut Bound<T>` 转换为 `Bound<&mut T>`。
    #[inline]
    #[unstable(feature = "bound_as_ref", issue = "80996")]
    pub fn as_mut(&mut self) -> Bound<&mut T> {
        match *self {
            Included(ref mut x) => Included(x),
            Excluded(ref mut x) => Excluded(x),
            Unbounded => Unbounded,
        }
    }

    /// 映射一个 `Bound` 通过将函数应用于包含的值 (包括 `Included` 和 `Excluded`)，返回相同类型的 `Bound`。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(bound_map)]
    /// use std::ops::Bound::*;
    ///
    /// let bound_string = Included("Hello, World!");
    ///
    /// assert_eq!(bound_string.map(|s| s.len()), Included(13));
    /// ```
    ///
    /// ```
    /// #![feature(bound_map)]
    /// use std::ops::Bound;
    /// use Bound::*;
    ///
    /// let unbounded_string: Bound<String> = Unbounded;
    ///
    /// assert_eq!(unbounded_string.map(|s| s.len()), Unbounded);
    /// ```
    #[inline]
    #[unstable(feature = "bound_map", issue = "86026")]
    pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Bound<U> {
        match self {
            Unbounded => Unbounded,
            Included(x) => Included(f(x)),
            Excluded(x) => Excluded(f(x)),
        }
    }
}

impl<T: Clone> Bound<&T> {
    /// Map 通过克隆绑定的内容将 `Bound<&T>` 更改为 `Bound<T>`。
    ///
    /// # Examples
    ///
    /// ```
    /// use std::ops::Bound::*;
    /// use std::ops::RangeBounds;
    ///
    /// assert_eq!((1..12).start_bound(), Included(&1));
    /// assert_eq!((1..12).start_bound().cloned(), Included(1));
    /// ```
    #[stable(feature = "bound_cloned", since = "1.55.0")]
    pub fn cloned(self) -> Bound<T> {
        match self {
            Bound::Unbounded => Bound::Unbounded,
            Bound::Included(x) => Bound::Included(x.clone()),
            Bound::Excluded(x) => Bound::Excluded(x.clone()),
        }
    }
}

/// `RangeBounds` 由 Rust 的内置范围类型实现，该范围类型由范围语法 (例如 `..`，`a..`，`..b`，`..=c`，`d..e` 或 `f..=g`) 产生。
///
#[stable(feature = "collections_range", since = "1.28.0")]
pub trait RangeBounds<T: ?Sized> {
    /// 开始索引绑定。
    ///
    /// 以 `Bound` 形式返回起始值。
    ///
    /// # Examples
    ///
    /// ```
    /// # fn main() {
    /// use std::ops::Bound::*;
    /// use std::ops::RangeBounds;
    ///
    /// assert_eq!((..10).start_bound(), Unbounded);
    /// assert_eq!((3..10).start_bound(), Included(&3));
    /// # }
    /// ```
    #[stable(feature = "collections_range", since = "1.28.0")]
    fn start_bound(&self) -> Bound<&T>;

    /// 结束索引绑定。
    ///
    /// 将结束值返回为 `Bound`。
    ///
    /// # Examples
    ///
    /// ```
    /// # fn main() {
    /// use std::ops::Bound::*;
    /// use std::ops::RangeBounds;
    ///
    /// assert_eq!((3..).end_bound(), Unbounded);
    /// assert_eq!((3..10).end_bound(), Excluded(&10));
    /// # }
    /// ```
    #[stable(feature = "collections_range", since = "1.28.0")]
    fn end_bound(&self) -> Bound<&T>;

    /// 如果范围中包含 `item`，则返回 `true`。
    ///
    /// # Examples
    ///
    /// ```
    /// assert!( (3..5).contains(&4));
    /// assert!(!(3..5).contains(&2));
    ///
    /// assert!( (0.0..1.0).contains(&0.5));
    /// assert!(!(0.0..1.0).contains(&f32::NAN));
    /// assert!(!(0.0..f32::NAN).contains(&0.5));
    /// assert!(!(f32::NAN..1.0).contains(&0.5));
    #[stable(feature = "range_contains", since = "1.35.0")]
    fn contains<U>(&self, item: &U) -> bool
    where
        T: PartialOrd<U>,
        U: ?Sized + PartialOrd<T>,
    {
        (match self.start_bound() {
            Included(ref start) => *start <= item,
            Excluded(ref start) => *start < item,
            Unbounded => true,
        }) && (match self.end_bound() {
            Included(ref end) => item <= *end,
            Excluded(ref end) => item < *end,
            Unbounded => true,
        })
    }
}

use self::Bound::{Excluded, Included, Unbounded};

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T: ?Sized> RangeBounds<T> for RangeFull {
    fn start_bound(&self) -> Bound<&T> {
        Unbounded
    }
    fn end_bound(&self) -> Bound<&T> {
        Unbounded
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeFrom<T> {
    fn start_bound(&self) -> Bound<&T> {
        Included(&self.start)
    }
    fn end_bound(&self) -> Bound<&T> {
        Unbounded
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeTo<T> {
    fn start_bound(&self) -> Bound<&T> {
        Unbounded
    }
    fn end_bound(&self) -> Bound<&T> {
        Excluded(&self.end)
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for Range<T> {
    fn start_bound(&self) -> Bound<&T> {
        Included(&self.start)
    }
    fn end_bound(&self) -> Bound<&T> {
        Excluded(&self.end)
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeInclusive<T> {
    fn start_bound(&self) -> Bound<&T> {
        Included(&self.start)
    }
    fn end_bound(&self) -> Bound<&T> {
        if self.exhausted {
            // 当迭代器用尽时，我们通常有 start == end，但我们希望范围显示为空，不包含任何内容。
            //
            Excluded(&self.end)
        } else {
            Included(&self.end)
        }
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeToInclusive<T> {
    fn start_bound(&self) -> Bound<&T> {
        Unbounded
    }
    fn end_bound(&self) -> Bound<&T> {
        Included(&self.end)
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for (Bound<T>, Bound<T>) {
    fn start_bound(&self) -> Bound<&T> {
        match *self {
            (Included(ref start), _) => Included(start),
            (Excluded(ref start), _) => Excluded(start),
            (Unbounded, _) => Unbounded,
        }
    }

    fn end_bound(&self) -> Bound<&T> {
        match *self {
            (_, Included(ref end)) => Included(end),
            (_, Excluded(ref end)) => Excluded(end),
            (_, Unbounded) => Unbounded,
        }
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<'a, T: ?Sized + 'a> RangeBounds<T> for (Bound<&'a T>, Bound<&'a T>) {
    fn start_bound(&self) -> Bound<&T> {
        self.0
    }

    fn end_bound(&self) -> Bound<&T> {
        self.1
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeFrom<&T> {
    fn start_bound(&self) -> Bound<&T> {
        Included(self.start)
    }
    fn end_bound(&self) -> Bound<&T> {
        Unbounded
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeTo<&T> {
    fn start_bound(&self) -> Bound<&T> {
        Unbounded
    }
    fn end_bound(&self) -> Bound<&T> {
        Excluded(self.end)
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for Range<&T> {
    fn start_bound(&self) -> Bound<&T> {
        Included(self.start)
    }
    fn end_bound(&self) -> Bound<&T> {
        Excluded(self.end)
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeInclusive<&T> {
    fn start_bound(&self) -> Bound<&T> {
        Included(self.start)
    }
    fn end_bound(&self) -> Bound<&T> {
        Included(self.end)
    }
}

#[stable(feature = "collections_range", since = "1.28.0")]
impl<T> RangeBounds<T> for RangeToInclusive<&T> {
    fn start_bound(&self) -> Bound<&T> {
        Unbounded
    }
    fn end_bound(&self) -> Bound<&T> {
        Included(self.end)
    }
}