range.rs.html -- source
Description: Source to the Rust file `src/libcore/ops/range.rs`.
Keywords: rust, rustlang, rust-lang

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    use fmt;
    use hash::{Hash, Hasher};

    /// An unbounded range (`..`).
    ///
    /// `RangeFull` is primarily used as a [slicing index], its shorthand is `..`.
    /// It cannot serve as an [`Iterator`] because it doesn't have a starting point.
    ///
    /// # Examples
    ///
    /// The `..` syntax is a `RangeFull`:
    ///
    /// ```
    /// assert_eq!((..), std::ops::RangeFull);
    /// ```
    ///
    /// It does not have an [`IntoIterator`] implementation, so you can't use it in
    /// a `for` loop directly. This won't compile:
    ///
    /// ```compile_fail,E0277
    /// for i in .. {
    ///    // ...
    /// }
    /// ```
    ///
    /// Used as a [slicing index], `RangeFull` produces the full array as a slice.
    ///
    /// ```
    /// let arr = [0, 1, 2, 3];
    /// assert_eq!(arr[ .. ], [0,1,2,3]);  // RangeFull
    /// assert_eq!(arr[ ..3], [0,1,2  ]);
    /// assert_eq!(arr[1.. ], [  1,2,3]);
    /// assert_eq!(arr[1..3], [  1,2  ]);
    /// ```
    ///
    /// [`IntoIterator`]: ../iter/trait.Iterator.html
    /// [`Iterator`]: ../iter/trait.IntoIterator.html
    /// [slicing index]: ../slice/trait.SliceIndex.html
    #[doc(alias = "..")]
    #[derive(Copy, Clone, 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, "..")
        }
    }

    /// A (half-open) range bounded inclusively below and exclusively above
    /// (`start..end`).
    ///
    /// The `Range` `start..end` contains all values with `x >= start` and
    /// `x < end`.  It is empty unless `start < end`.
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!((3..5), std::ops::Range { start: 3, end: 5 });
    /// assert_eq!(3 + 4 + 5, (3..6).sum());
    ///
    /// let arr = ['a', 'b', 'c', 'd'];
    /// assert_eq!(arr[ .. ], ['a', 'b', 'c', 'd']);
    /// assert_eq!(arr[ ..3], ['a', 'b', 'c',    ]);
    /// assert_eq!(arr[1.. ], [     'b', 'c', 'd']);
    /// assert_eq!(arr[1..3], [     'b', 'c'     ]);  // Range
    /// ```
    #[doc(alias = "..")]
    #[derive(Clone, PartialEq, Eq, Hash)]  // not Copy -- see #27186
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct Range<Idx> {
        /// The lower bound of the range (inclusive).
        #[stable(feature = "rust1", since = "1.0.0")]
        pub start: Idx,
        /// The upper bound of the range (exclusive).
        #[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 {
            write!(fmt, "{:?}..{:?}", self.start, self.end)
        }
    }

    impl<Idx: PartialOrd<Idx>> Range<Idx> {
        /// Returns `true` if `item` is contained in the range.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(range_contains)]
        ///
        /// use std::f32;
        ///
        /// 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));
        /// ```
        #[unstable(feature = "range_contains", reason = "recently added as per RFC", issue = "32311")]
        pub fn contains<U>(&self, item: &U) -> bool
        where
            Idx: PartialOrd<U>,
            U: ?Sized + PartialOrd<Idx>,
        {
            <Self as RangeBounds<Idx>>::contains(self, item)
        }

        /// Returns `true` if the range contains no items.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(range_is_empty)]
        ///
        /// assert!(!(3..5).is_empty());
        /// assert!( (3..3).is_empty());
        /// assert!( (3..2).is_empty());
        /// ```
        ///
        /// The range is empty if either side is incomparable:
        ///
        /// ```
        /// #![feature(range_is_empty)]
        ///
        /// use std::f32::NAN;
        /// assert!(!(3.0..5.0).is_empty());
        /// assert!( (3.0..NAN).is_empty());
        /// assert!( (NAN..5.0).is_empty());
        /// ```
        #[unstable(feature = "range_is_empty", reason = "recently added", issue = "48111")]
        pub fn is_empty(&self) -> bool {
            !(self.start < self.end)
        }
    }

    /// A range only bounded inclusively below (`start..`).
    ///
    /// The `RangeFrom` `start..` contains all values with `x >= start`.
    ///
    /// *Note*: Currently, no overflow checking is done for the [`Iterator`]
    /// implementation; if you use an integer range and the integer overflows, it
    /// might panic in debug mode or create an endless loop in release mode. **This
    /// overflow behavior might change in the future.**
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!((2..), std::ops::RangeFrom { start: 2 });
    /// assert_eq!(2 + 3 + 4, (2..).take(3).sum());
    ///
    /// let arr = [0, 1, 2, 3];
    /// assert_eq!(arr[ .. ], [0,1,2,3]);
    /// assert_eq!(arr[ ..3], [0,1,2  ]);
    /// assert_eq!(arr[1.. ], [  1,2,3]);  // RangeFrom
    /// assert_eq!(arr[1..3], [  1,2  ]);
    /// ```
    ///
    /// [`Iterator`]: ../iter/trait.IntoIterator.html
    #[doc(alias = "..")]
    #[derive(Clone, PartialEq, Eq, Hash)]  // not Copy -- see #27186
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct RangeFrom<Idx> {
        /// The lower bound of the range (inclusive).
        #[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 {
            write!(fmt, "{:?}..", self.start)
        }
    }

    impl<Idx: PartialOrd<Idx>> RangeFrom<Idx> {
        /// Returns `true` if `item` is contained in the range.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(range_contains)]
        ///
        /// use std::f32;
        ///
        /// 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));
        /// ```
        #[unstable(feature = "range_contains", reason = "recently added as per RFC", issue = "32311")]
        pub fn contains<U>(&self, item: &U) -> bool
        where
            Idx: PartialOrd<U>,
            U: ?Sized + PartialOrd<Idx>,
        {
            <Self as RangeBounds<Idx>>::contains(self, item)
        }
    }

    /// A range only bounded exclusively above (`..end`).
    ///
    /// The `RangeTo` `..end` contains all values with `x < end`.
    /// It cannot serve as an [`Iterator`] because it doesn't have a starting point.
    ///
    /// # Examples
    ///
    /// The `..end` syntax is a `RangeTo`:
    ///
    /// ```
    /// assert_eq!((..5), std::ops::RangeTo { end: 5 });
    /// ```
    ///
    /// It does not have an [`IntoIterator`] implementation, so you can't use it in
    /// a `for` loop directly. This won't compile:
    ///
    /// ```compile_fail,E0277
    /// // error[E0277]: the trait bound `std::ops::RangeTo<{integer}>:
    /// // std::iter::Iterator` is not satisfied
    /// for i in ..5 {
    ///     // ...
    /// }
    /// ```
    ///
    /// When used as a [slicing index], `RangeTo` produces a slice of all array
    /// elements before the index indicated by `end`.
    ///
    /// ```
    /// let arr = [0, 1, 2, 3];
    /// assert_eq!(arr[ .. ], [0,1,2,3]);
    /// assert_eq!(arr[ ..3], [0,1,2  ]);  // RangeTo
    /// assert_eq!(arr[1.. ], [  1,2,3]);
    /// assert_eq!(arr[1..3], [  1,2  ]);
    /// ```
    ///
    /// [`IntoIterator`]: ../iter/trait.Iterator.html
    /// [`Iterator`]: ../iter/trait.IntoIterator.html
    /// [slicing index]: ../slice/trait.SliceIndex.html
    #[doc(alias = "..")]
    #[derive(Copy, Clone, PartialEq, Eq, Hash)]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct RangeTo<Idx> {
        /// The upper bound of the range (exclusive).
        #[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)
        }
    }

    impl<Idx: PartialOrd<Idx>> RangeTo<Idx> {
        /// Returns `true` if `item` is contained in the range.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(range_contains)]
        ///
        /// use std::f32;
        ///
        /// 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));
        /// ```
        #[unstable(feature = "range_contains", reason = "recently added as per RFC", issue = "32311")]
        pub fn contains<U>(&self, item: &U) -> bool
        where
            Idx: PartialOrd<U>,
            U: ?Sized + PartialOrd<Idx>,
        {
            <Self as RangeBounds<Idx>>::contains(self, item)
        }
    }

    /// A range bounded inclusively below and above (`start..=end`).
    ///
    /// The `RangeInclusive` `start..=end` contains all values with `x >= start`
    /// and `x <= end`.  It is empty unless `start <= end`.
    ///
    /// This iterator is [fused], but the specific values of `start` and `end` after
    /// iteration has finished are **unspecified** other than that [`.is_empty()`]
    /// will return `true` once no more values will be produced.
    ///
    /// [fused]: ../iter/trait.FusedIterator.html
    /// [`.is_empty()`]: #method.is_empty
    ///
    /// # Examples
    ///
    /// ```
    /// assert_eq!((3..=5), std::ops::RangeInclusive::new(3, 5));
    /// assert_eq!(3 + 4 + 5, (3..=5).sum());
    ///
    /// let arr = [0, 1, 2, 3];
    /// assert_eq!(arr[ ..=2], [0,1,2  ]);
    /// assert_eq!(arr[1..=2], [  1,2  ]);  // RangeInclusive
    /// ```
    #[doc(alias = "..=")]
    #[derive(Clone)]  // not Copy -- see #27186
    #[stable(feature = "inclusive_range", since = "1.26.0")]
    pub struct RangeInclusive<Idx> {
        pub(crate) start: Idx,
        pub(crate) end: Idx,
        pub(crate) is_empty: Option<bool>,
        // This field is:
        //  - `None` when next() or next_back() was never called
        //  - `Some(false)` when `start <= end` assuming no overflow
        //  - `Some(true)` otherwise
        // The field cannot be a simple `bool` because the `..=` constructor can
        // accept non-PartialOrd types, also we want the constructor to be const.
    }

    trait RangeInclusiveEquality: Sized {
        fn canonicalized_is_empty(range: &RangeInclusive<Self>) -> bool;
    }
    impl<T> RangeInclusiveEquality for T {
        #[inline]
        default fn canonicalized_is_empty(range: &RangeInclusive<Self>) -> bool {
            range.is_empty.unwrap_or_default()
        }
    }
    impl<T: PartialOrd> RangeInclusiveEquality for T {
        #[inline]
        fn canonicalized_is_empty(range: &RangeInclusive<Self>) -> bool {
            range.is_empty()
        }
    }

    #[stable(feature = "inclusive_range", since = "1.26.0")]
    impl<Idx: PartialEq> PartialEq for RangeInclusive<Idx> {
        #[inline]
        fn eq(&self, other: &Self) -> bool {
            self.start == other.start && self.end == other.end
                && RangeInclusiveEquality::canonicalized_is_empty(self)
                    == RangeInclusiveEquality::canonicalized_is_empty(other)
        }
    }

    #[stable(feature = "inclusive_range", since = "1.26.0")]
    impl<Idx: Eq> Eq for RangeInclusive<Idx> {}

    #[stable(feature = "inclusive_range", since = "1.26.0")]
    impl<Idx: Hash> Hash for RangeInclusive<Idx> {
        fn hash<H: Hasher>(&self, state: &mut H) {
            self.start.hash(state);
            self.end.hash(state);
            RangeInclusiveEquality::canonicalized_is_empty(self).hash(state);
        }
    }

    impl<Idx> RangeInclusive<Idx> {
        /// Creates a new inclusive range. Equivalent to writing `start..=end`.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::ops::RangeInclusive;
        ///
        /// assert_eq!(3..=5, RangeInclusive::new(3, 5));
        /// ```
        #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
        #[inline]
        #[rustc_promotable]
        pub const fn new(start: Idx, end: Idx) -> Self {
            Self { start, end, is_empty: None }
        }

        /// Returns the lower bound of the range (inclusive).
        ///
        /// When using an inclusive range for iteration, the values of `start()` and
        /// [`end()`] are unspecified after the iteration ended. To determine
        /// whether the inclusive range is empty, use the [`is_empty()`] method
        /// instead of comparing `start() > end()`.
        ///
        /// Note: the value returned by this method is unspecified after the range
        /// has been iterated to exhaustion.
        ///
        /// [`end()`]: #method.end
        /// [`is_empty()`]: #method.is_empty
        ///
        /// # Examples
        ///
        /// ```
        /// assert_eq!((3..=5).start(), &3);
        /// ```
        #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
        #[inline]
        pub const fn start(&self) -> &Idx {
            &self.start
        }

        /// Returns the upper bound of the range (inclusive).
        ///
        /// When using an inclusive range for iteration, the values of [`start()`]
        /// and `end()` are unspecified after the iteration ended. To determine
        /// whether the inclusive range is empty, use the [`is_empty()`] method
        /// instead of comparing `start() > end()`.
        ///
        /// Note: the value returned by this method is unspecified after the range
        /// has been iterated to exhaustion.
        ///
        /// [`start()`]: #method.start
        /// [`is_empty()`]: #method.is_empty
        ///
        /// # Examples
        ///
        /// ```
        /// assert_eq!((3..=5).end(), &5);
        /// ```
        #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
        #[inline]
        pub const fn end(&self) -> &Idx {
            &self.end
        }

        /// Destructures the `RangeInclusive` into (lower bound, upper (inclusive) bound).
        ///
        /// Note: the value returned by this method is unspecified after the range
        /// has been iterated to exhaustion.
        ///
        /// # 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)
        }
    }

    #[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 {
            write!(fmt, "{:?}..={:?}", self.start, self.end)
        }
    }

    impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
        /// Returns `true` if `item` is contained in the range.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(range_contains)]
        ///
        /// use std::f32;
        ///
        /// 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));
        /// ```
        #[unstable(feature = "range_contains", reason = "recently added as per RFC", issue = "32311")]
        pub fn contains<U>(&self, item: &U) -> bool
        where
            Idx: PartialOrd<U>,
            U: ?Sized + PartialOrd<Idx>,
        {
            <Self as RangeBounds<Idx>>::contains(self, item)
        }

        /// Returns `true` if the range contains no items.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(range_is_empty)]
        ///
        /// assert!(!(3..=5).is_empty());
        /// assert!(!(3..=3).is_empty());
        /// assert!( (3..=2).is_empty());
        /// ```
        ///
        /// The range is empty if either side is incomparable:
        ///
        /// ```
        /// #![feature(range_is_empty)]
        ///
        /// use std::f32::NAN;
        /// assert!(!(3.0..=5.0).is_empty());
        /// assert!( (3.0..=NAN).is_empty());
        /// assert!( (NAN..=5.0).is_empty());
        /// ```
        ///
        /// This method returns `true` after iteration has finished:
        ///
        /// ```
        /// #![feature(range_is_empty)]
        ///
        /// let mut r = 3..=5;
        /// for _ in r.by_ref() {}
        /// // Precise field values are unspecified here
        /// assert!(r.is_empty());
        /// ```
        #[unstable(feature = "range_is_empty", reason = "recently added", issue = "48111")]
        #[inline]
        pub fn is_empty(&self) -> bool {
            self.is_empty.unwrap_or_else(|| !(self.start <= self.end))
        }

        // If this range's `is_empty` is field is unknown (`None`), update it to be a concrete value.
        #[inline]
        pub(crate) fn compute_is_empty(&mut self) {
            if self.is_empty.is_none() {
                self.is_empty = Some(!(self.start <= self.end));
            }
        }
    }

    /// A range only bounded inclusively above (`..=end`).
    ///
    /// The `RangeToInclusive` `..=end` contains all values with `x <= end`.
    /// It cannot serve as an [`Iterator`] because it doesn't have a starting point.
    ///
    /// # Examples
    ///
    /// The `..=end` syntax is a `RangeToInclusive`:
    ///
    /// ```
    /// assert_eq!((..=5), std::ops::RangeToInclusive{ end: 5 });
    /// ```
    ///
    /// It does not have an [`IntoIterator`] implementation, so you can't use it in a
    /// `for` loop directly. This won't compile:
    ///
    /// ```compile_fail,E0277
    /// // error[E0277]: the trait bound `std::ops::RangeToInclusive<{integer}>:
    /// // std::iter::Iterator` is not satisfied
    /// for i in ..=5 {
    ///     // ...
    /// }
    /// ```
    ///
    /// When used as a [slicing index], `RangeToInclusive` produces a slice of all
    /// array elements up to and including the index indicated by `end`.
    ///
    /// ```
    /// let arr = [0, 1, 2, 3];
    /// assert_eq!(arr[ ..=2], [0,1,2  ]);  // RangeToInclusive
    /// assert_eq!(arr[1..=2], [  1,2  ]);
    /// ```
    ///
    /// [`IntoIterator`]: ../iter/trait.Iterator.html
    /// [`Iterator`]: ../iter/trait.IntoIterator.html
    /// [slicing index]: ../slice/trait.SliceIndex.html
    #[doc(alias = "..=")]
    #[derive(Copy, Clone, PartialEq, Eq, Hash)]
    #[stable(feature = "inclusive_range", since = "1.26.0")]
    pub struct RangeToInclusive<Idx> {
        /// The upper bound of the range (inclusive)
        #[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)
        }
    }

    #[unstable(feature = "range_contains", reason = "recently added as per RFC", issue = "32311")]
    impl<Idx: PartialOrd<Idx>> RangeToInclusive<Idx> {
        /// Returns `true` if `item` is contained in the range.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(range_contains)]
        ///
        /// use std::f32;
        ///
        /// 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));
        /// ```
        #[unstable(feature = "range_contains", reason = "recently added as per RFC", issue = "32311")]
        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> cannot impl From<RangeTo<Idx>>
    // because underflow would be possible with (..0).into()

    /// An endpoint of a range of keys.
    ///
    /// # Examples
    ///
    /// `Bound`s are range endpoints:
    ///
    /// ```
    /// 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));
    /// ```
    ///
    /// Using a tuple of `Bound`s as an argument to [`BTreeMap::range`].
    /// Note that in most cases, it's better to use range syntax (`1..5`) instead.
    ///
    /// ```
    /// 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> {
        /// An inclusive bound.
        #[stable(feature = "collections_bound", since = "1.17.0")]
        Included(#[stable(feature = "collections_bound", since = "1.17.0")] T),
        /// An exclusive bound.
        #[stable(feature = "collections_bound", since = "1.17.0")]
        Excluded(#[stable(feature = "collections_bound", since = "1.17.0")] T),
        /// An infinite endpoint. Indicates that there is no bound in this direction.
        #[stable(feature = "collections_bound", since = "1.17.0")]
        Unbounded,
    }

    #[stable(feature = "collections_range", since = "1.28.0")]
    /// `RangeBounds` is implemented by Rust's built-in range types, produced
    /// by range syntax like `..`, `a..`, `..b` or `c..d`.
    pub trait RangeBounds<T: ?Sized> {
        /// Start index bound.
        ///
        /// Returns the start value as a `Bound`.
        ///
        /// # 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>;

        /// End index bound.
        ///
        /// Returns the end value as a `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>;

        /// Returns `true` if `item` is contained in the range.
        ///
        /// # Examples
        ///
        /// ```
        /// #![feature(range_contains)]
        ///
        /// use std::f32;
        ///
        /// 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));
        #[unstable(feature = "range_contains", reason = "recently added as per RFC", issue = "32311")]
        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> {
            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)
        }
    }

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