#
core/ops/
range.rs

    1use crate::fmt;
    2use crate::hash::Hash;
    3
    4/// An unbounded range (`..`).
    5///
    6/// `RangeFull` is primarily used as a [slicing index], its shorthand is `..`.
    7/// It cannot serve as an [`Iterator`] because it doesn't have a starting point.
    8///
    9/// # Examples
    10///
    11/// The `..` syntax is a `RangeFull`:
    12///
    13/// ```
    14/// assert_eq!(.., std::ops::RangeFull);
    15/// ```
    16///
    17/// It does not have an [`IntoIterator`] implementation, so you can't use it in
    18/// a `for` loop directly. This won't compile:
    19///
    20/// ```compile_fail,E0277
    21/// for i in .. {
    22///     // ...
    23/// }
    24/// ```
    25///
    26/// Used as a [slicing index], `RangeFull` produces the full array as a slice.
    27///
    28/// ```
    29/// let arr = [0, 1, 2, 3, 4];
    30/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]); // This is the `RangeFull`
    31/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
    32/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
    33/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
    34/// assert_eq!(arr[1.. 3], [   1, 2      ]);
    35/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
    36/// ```
    37///
    38/// [slicing index]: crate::slice::SliceIndex
    39#[lang = "RangeFull"]
    40#[doc(alias = "..")]
    41#[derive(Copy, Clone, Default, PartialEq, Eq, Hash)]
    42#[stable(feature = "rust1", since = "1.0.0")]
    43pub struct RangeFull;
    44
    45#[stable(feature = "rust1", since = "1.0.0")]
    46impl fmt::Debug for RangeFull {
    47    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
    48        write!(fmt, "..")
    49    }
    50}
    51
    52/// A (half-open) range bounded inclusively below and exclusively above
    53/// (`start..end`).
    54///
    55/// The range `start..end` contains all values with `start <= x < end`.
    56/// It is empty if `start >= end`.
    57///
    58/// # Examples
    59///
    60/// The `start..end` syntax is a `Range`:
    61///
    62/// ```
    63/// assert_eq!((3..5), std::ops::Range { start: 3, end: 5 });
    64/// assert_eq!(3 + 4 + 5, (3..6).sum());
    65/// ```
    66///
    67/// ```
    68/// let arr = [0, 1, 2, 3, 4];
    69/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
    70/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
    71/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
    72/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
    73/// assert_eq!(arr[1.. 3], [   1, 2      ]); // This is a `Range`
    74/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
    75/// ```
    76#[lang = "Range"]
    77#[doc(alias = "..")]
    78#[derive(Clone, Default, PartialEq, Eq, Hash)] // not Copy -- see #27186
    79#[stable(feature = "rust1", since = "1.0.0")]
    80pub struct Range<Idx> {
    81    /// The lower bound of the range (inclusive).
    82    #[stable(feature = "rust1", since = "1.0.0")]
    83    pub start: Idx,
    84    /// The upper bound of the range (exclusive).
    85    #[stable(feature = "rust1", since = "1.0.0")]
    86    pub end: Idx,
    87}
    88
    89#[stable(feature = "rust1", since = "1.0.0")]
    90impl<Idx: fmt::Debug> fmt::Debug for Range<Idx> {
    91    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
    92        self.start.fmt(fmt)?;
    93        write!(fmt, "..")?;
    94        self.end.fmt(fmt)?;
    95        Ok(())
    96    }
    97}
    98
    99impl<Idx: PartialOrd<Idx>> Range<Idx> {
    100    /// Returns `true` if `item` is contained in the range.
    101    ///
    102    /// # Examples
    103    ///
    104    /// ```
    105    /// assert!(!(3..5).contains(&2));
    106    /// assert!( (3..5).contains(&3));
    107    /// assert!( (3..5).contains(&4));
    108    /// assert!(!(3..5).contains(&5));
    109    ///
    110    /// assert!(!(3..3).contains(&3));
    111    /// assert!(!(3..2).contains(&3));
    112    ///
    113    /// assert!( (0.0..1.0).contains(&0.5));
    114    /// assert!(!(0.0..1.0).contains(&f32::NAN));
    115    /// assert!(!(0.0..f32::NAN).contains(&0.5));
    116    /// assert!(!(f32::NAN..1.0).contains(&0.5));
    117    /// ```
    118    #[inline]
    119    #[stable(feature = "range_contains", since = "1.35.0")]
    120    pub fn contains<U>(&self, item: &U) -> bool
    121    where
    122        Idx: PartialOrd<U>,
    123        U: ?Sized + PartialOrd<Idx>,
    124    {
    125        <Self as RangeBounds<Idx>>::contains(self, item)
    126    }
    127
    128    /// Returns `true` if the range contains no items.
    129    ///
    130    /// # Examples
    131    ///
    132    /// ```
    133    /// assert!(!(3..5).is_empty());
    134    /// assert!( (3..3).is_empty());
    135    /// assert!( (3..2).is_empty());
    136    /// ```
    137    ///
    138    /// The range is empty if either side is incomparable:
    139    ///
    140    /// ```
    141    /// assert!(!(3.0..5.0).is_empty());
    142    /// assert!( (3.0..f32::NAN).is_empty());
    143    /// assert!( (f32::NAN..5.0).is_empty());
    144    /// ```
    145    #[inline]
    146    #[stable(feature = "range_is_empty", since = "1.47.0")]
    147    pub fn is_empty(&self) -> bool {
    148        !(self.start < self.end)
    149    }
    150}
    151
    152/// A range only bounded inclusively below (`start..`).
    153///
    154/// The `RangeFrom` `start..` contains all values with `x >= start`.
    155///
    156/// *Note*: Overflow in the [`Iterator`] implementation (when the contained
    157/// data type reaches its numerical limit) is allowed to panic, wrap, or
    158/// saturate. This behavior is defined by the implementation of the [`Step`]
    159/// trait. For primitive integers, this follows the normal rules, and respects
    160/// the overflow checks profile (panic in debug, wrap in release). Note also
    161/// that overflow happens earlier than you might assume: the overflow happens
    162/// in the call to `next` that yields the maximum value, as the range must be
    163/// set to a state to yield the next value.
    164///
    165/// [`Step`]: crate::iter::Step
    166///
    167/// # Examples
    168///
    169/// The `start..` syntax is a `RangeFrom`:
    170///
    171/// ```
    172/// assert_eq!((2..), std::ops::RangeFrom { start: 2 });
    173/// assert_eq!(2 + 3 + 4, (2..).take(3).sum());
    174/// ```
    175///
    176/// ```
    177/// let arr = [0, 1, 2, 3, 4];
    178/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
    179/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
    180/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
    181/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]); // This is a `RangeFrom`
    182/// assert_eq!(arr[1.. 3], [   1, 2      ]);
    183/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
    184/// ```
    185#[lang = "RangeFrom"]
    186#[doc(alias = "..")]
    187#[derive(Clone, PartialEq, Eq, Hash)] // not Copy -- see #27186
    188#[stable(feature = "rust1", since = "1.0.0")]
    189pub struct RangeFrom<Idx> {
    190    /// The lower bound of the range (inclusive).
    191    #[stable(feature = "rust1", since = "1.0.0")]
    192    pub start: Idx,
    193}
    194
    195#[stable(feature = "rust1", since = "1.0.0")]
    196impl<Idx: fmt::Debug> fmt::Debug for RangeFrom<Idx> {
    197    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
    198        self.start.fmt(fmt)?;
    199        write!(fmt, "..")?;
    200        Ok(())
    201    }
    202}
    203
    204impl<Idx: PartialOrd<Idx>> RangeFrom<Idx> {
    205    /// Returns `true` if `item` is contained in the range.
    206    ///
    207    /// # Examples
    208    ///
    209    /// ```
    210    /// assert!(!(3..).contains(&2));
    211    /// assert!( (3..).contains(&3));
    212    /// assert!( (3..).contains(&1_000_000_000));
    213    ///
    214    /// assert!( (0.0..).contains(&0.5));
    215    /// assert!(!(0.0..).contains(&f32::NAN));
    216    /// assert!(!(f32::NAN..).contains(&0.5));
    217    /// ```
    218    #[inline]
    219    #[stable(feature = "range_contains", since = "1.35.0")]
    220    pub fn contains<U>(&self, item: &U) -> bool
    221    where
    222        Idx: PartialOrd<U>,
    223        U: ?Sized + PartialOrd<Idx>,
    224    {
    225        <Self as RangeBounds<Idx>>::contains(self, item)
    226    }
    227}
    228
    229/// A range only bounded exclusively above (`..end`).
    230///
    231/// The `RangeTo` `..end` contains all values with `x < end`.
    232/// It cannot serve as an [`Iterator`] because it doesn't have a starting point.
    233///
    234/// # Examples
    235///
    236/// The `..end` syntax is a `RangeTo`:
    237///
    238/// ```
    239/// assert_eq!((..5), std::ops::RangeTo { end: 5 });
    240/// ```
    241///
    242/// It does not have an [`IntoIterator`] implementation, so you can't use it in
    243/// a `for` loop directly. This won't compile:
    244///
    245/// ```compile_fail,E0277
    246/// // error[E0277]: the trait bound `std::ops::RangeTo<{integer}>:
    247/// // std::iter::Iterator` is not satisfied
    248/// for i in ..5 {
    249///     // ...
    250/// }
    251/// ```
    252///
    253/// When used as a [slicing index], `RangeTo` produces a slice of all array
    254/// elements before the index indicated by `end`.
    255///
    256/// ```
    257/// let arr = [0, 1, 2, 3, 4];
    258/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
    259/// assert_eq!(arr[ .. 3], [0, 1, 2      ]); // This is a `RangeTo`
    260/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
    261/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
    262/// assert_eq!(arr[1.. 3], [   1, 2      ]);
    263/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
    264/// ```
    265///
    266/// [slicing index]: crate::slice::SliceIndex
    267#[lang = "RangeTo"]
    268#[doc(alias = "..")]
    269#[derive(Copy, Clone, PartialEq, Eq, Hash)]
    270#[stable(feature = "rust1", since = "1.0.0")]
    271pub struct RangeTo<Idx> {
    272    /// The upper bound of the range (exclusive).
    273    #[stable(feature = "rust1", since = "1.0.0")]
    274    pub end: Idx,
    275}
    276
    277#[stable(feature = "rust1", since = "1.0.0")]
    278impl<Idx: fmt::Debug> fmt::Debug for RangeTo<Idx> {
    279    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
    280        write!(fmt, "..")?;
    281        self.end.fmt(fmt)?;
    282        Ok(())
    283    }
    284}
    285
    286impl<Idx: PartialOrd<Idx>> RangeTo<Idx> {
    287    /// Returns `true` if `item` is contained in the range.
    288    ///
    289    /// # Examples
    290    ///
    291    /// ```
    292    /// assert!( (..5).contains(&-1_000_000_000));
    293    /// assert!( (..5).contains(&4));
    294    /// assert!(!(..5).contains(&5));
    295    ///
    296    /// assert!( (..1.0).contains(&0.5));
    297    /// assert!(!(..1.0).contains(&f32::NAN));
    298    /// assert!(!(..f32::NAN).contains(&0.5));
    299    /// ```
    300    #[inline]
    301    #[stable(feature = "range_contains", since = "1.35.0")]
    302    pub fn contains<U>(&self, item: &U) -> bool
    303    where
    304        Idx: PartialOrd<U>,
    305        U: ?Sized + PartialOrd<Idx>,
    306    {
    307        <Self as RangeBounds<Idx>>::contains(self, item)
    308    }
    309}
    310
    311/// A range bounded inclusively below and above (`start..=end`).
    312///
    313/// The `RangeInclusive` `start..=end` contains all values with `x >= start`
    314/// and `x <= end`. It is empty unless `start <= end`.
    315///
    316/// This iterator is [fused], but the specific values of `start` and `end` after
    317/// iteration has finished are **unspecified** other than that [`.is_empty()`]
    318/// will return `true` once no more values will be produced.
    319///
    320/// [fused]: crate::iter::FusedIterator
    321/// [`.is_empty()`]: RangeInclusive::is_empty
    322///
    323/// # Examples
    324///
    325/// The `start..=end` syntax is a `RangeInclusive`:
    326///
    327/// ```
    328/// assert_eq!((3..=5), std::ops::RangeInclusive::new(3, 5));
    329/// assert_eq!(3 + 4 + 5, (3..=5).sum());
    330/// ```
    331///
    332/// ```
    333/// let arr = [0, 1, 2, 3, 4];
    334/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
    335/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
    336/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
    337/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
    338/// assert_eq!(arr[1.. 3], [   1, 2      ]);
    339/// assert_eq!(arr[1..=3], [   1, 2, 3   ]); // This is a `RangeInclusive`
    340/// ```
    341#[lang = "RangeInclusive"]
    342#[doc(alias = "..=")]
    343#[derive(Clone, PartialEq, Eq, Hash)] // not Copy -- see #27186
    344#[stable(feature = "inclusive_range", since = "1.26.0")]
    345pub struct RangeInclusive<Idx> {
    346    // Note that the fields here are not public to allow changing the
    347    // representation in the future; in particular, while we could plausibly
    348    // expose start/end, modifying them without changing (future/current)
    349    // private fields may lead to incorrect behavior, so we don't want to
    350    // support that mode.
    351    pub(crate) start: Idx,
    352    pub(crate) end: Idx,
    353
    354    // This field is:
    355    //  - `false` upon construction
    356    //  - `false` when iteration has yielded an element and the iterator is not exhausted
    357    //  - `true` when iteration has been used to exhaust the iterator
    358    //
    359    // This is required to support PartialEq and Hash without a PartialOrd bound or specialization.
    360    pub(crate) exhausted: bool,
    361}
    362
    363impl<Idx> RangeInclusive<Idx> {
    364    /// Creates a new inclusive range. Equivalent to writing `start..=end`.
    365    ///
    366    /// # Examples
    367    ///
    368    /// ```
    369    /// use std::ops::RangeInclusive;
    370    ///
    371    /// assert_eq!(3..=5, RangeInclusive::new(3, 5));
    372    /// ```
    373    #[lang = "range_inclusive_new"]
    374    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
    375    #[inline]
    376    #[rustc_promotable]
    377    #[rustc_const_stable(feature = "const_range_new", since = "1.32.0")]
    378    pub const fn new(start: Idx, end: Idx) -> Self {
    379        Self { start, end, exhausted: false }
    380    }
    381
    382    /// Returns the lower bound of the range (inclusive).
    383    ///
    384    /// When using an inclusive range for iteration, the values of `start()` and
    385    /// [`end()`] are unspecified after the iteration ended. To determine
    386    /// whether the inclusive range is empty, use the [`is_empty()`] method
    387    /// instead of comparing `start() > end()`.
    388    ///
    389    /// Note: the value returned by this method is unspecified after the range
    390    /// has been iterated to exhaustion.
    391    ///
    392    /// [`end()`]: RangeInclusive::end
    393    /// [`is_empty()`]: RangeInclusive::is_empty
    394    ///
    395    /// # Examples
    396    ///
    397    /// ```
    398    /// assert_eq!((3..=5).start(), &3);
    399    /// ```
    400    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
    401    #[rustc_const_stable(feature = "const_inclusive_range_methods", since = "1.32.0")]
    402    #[inline]
    403    pub const fn start(&self) -> &Idx {
    404        &self.start
    405    }
    406
    407    /// Returns the upper bound of the range (inclusive).
    408    ///
    409    /// When using an inclusive range for iteration, the values of [`start()`]
    410    /// and `end()` are unspecified after the iteration ended. To determine
    411    /// whether the inclusive range is empty, use the [`is_empty()`] method
    412    /// instead of comparing `start() > end()`.
    413    ///
    414    /// Note: the value returned by this method is unspecified after the range
    415    /// has been iterated to exhaustion.
    416    ///
    417    /// [`start()`]: RangeInclusive::start
    418    /// [`is_empty()`]: RangeInclusive::is_empty
    419    ///
    420    /// # Examples
    421    ///
    422    /// ```
    423    /// assert_eq!((3..=5).end(), &5);
    424    /// ```
    425    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
    426    #[rustc_const_stable(feature = "const_inclusive_range_methods", since = "1.32.0")]
    427    #[inline]
    428    pub const fn end(&self) -> &Idx {
    429        &self.end
    430    }
    431
    432    /// Destructures the `RangeInclusive` into (lower bound, upper (inclusive) bound).
    433    ///
    434    /// Note: the value returned by this method is unspecified after the range
    435    /// has been iterated to exhaustion.
    436    ///
    437    /// # Examples
    438    ///
    439    /// ```
    440    /// assert_eq!((3..=5).into_inner(), (3, 5));
    441    /// ```
    442    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
    443    #[inline]
    444    #[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
    445    pub const fn into_inner(self) -> (Idx, Idx) {
    446        (self.start, self.end)
    447    }
    448}
    449
    450impl RangeInclusive<usize> {
    451    /// Converts to an exclusive `Range` for `SliceIndex` implementations.
    452    /// The caller is responsible for dealing with `end == usize::MAX`.
    453    #[inline]
    454    pub(crate) const fn into_slice_range(self) -> Range<usize> {
    455        // If we're not exhausted, we want to simply slice `start..end + 1`.
    456        // If we are exhausted, then slicing with `end + 1..end + 1` gives us an
    457        // empty range that is still subject to bounds-checks for that endpoint.
    458        let exclusive_end = self.end + 1;
    459        let start = if self.exhausted { exclusive_end } else { self.start };
    460        start..exclusive_end
    461    }
    462}
    463
    464#[stable(feature = "inclusive_range", since = "1.26.0")]
    465impl<Idx: fmt::Debug> fmt::Debug for RangeInclusive<Idx> {
    466    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
    467        self.start.fmt(fmt)?;
    468        write!(fmt, "..=")?;
    469        self.end.fmt(fmt)?;
    470        if self.exhausted {
    471            write!(fmt, " (exhausted)")?;
    472        }
    473        Ok(())
    474    }
    475}
    476
    477impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
    478    /// Returns `true` if `item` is contained in the range.
    479    ///
    480    /// # Examples
    481    ///
    482    /// ```
    483    /// assert!(!(3..=5).contains(&2));
    484    /// assert!( (3..=5).contains(&3));
    485    /// assert!( (3..=5).contains(&4));
    486    /// assert!( (3..=5).contains(&5));
    487    /// assert!(!(3..=5).contains(&6));
    488    ///
    489    /// assert!( (3..=3).contains(&3));
    490    /// assert!(!(3..=2).contains(&3));
    491    ///
    492    /// assert!( (0.0..=1.0).contains(&1.0));
    493    /// assert!(!(0.0..=1.0).contains(&f32::NAN));
    494    /// assert!(!(0.0..=f32::NAN).contains(&0.0));
    495    /// assert!(!(f32::NAN..=1.0).contains(&1.0));
    496    /// ```
    497    ///
    498    /// This method always returns `false` after iteration has finished:
    499    ///
    500    /// ```
    501    /// let mut r = 3..=5;
    502    /// assert!(r.contains(&3) && r.contains(&5));
    503    /// for _ in r.by_ref() {}
    504    /// // Precise field values are unspecified here
    505    /// assert!(!r.contains(&3) && !r.contains(&5));
    506    /// ```
    507    #[inline]
    508    #[stable(feature = "range_contains", since = "1.35.0")]
    509    pub fn contains<U>(&self, item: &U) -> bool
    510    where
    511        Idx: PartialOrd<U>,
    512        U: ?Sized + PartialOrd<Idx>,
    513    {
    514        <Self as RangeBounds<Idx>>::contains(self, item)
    515    }
    516
    517    /// Returns `true` if the range contains no items.
    518    ///
    519    /// # Examples
    520    ///
    521    /// ```
    522    /// assert!(!(3..=5).is_empty());
    523    /// assert!(!(3..=3).is_empty());
    524    /// assert!( (3..=2).is_empty());
    525    /// ```
    526    ///
    527    /// The range is empty if either side is incomparable:
    528    ///
    529    /// ```
    530    /// assert!(!(3.0..=5.0).is_empty());
    531    /// assert!( (3.0..=f32::NAN).is_empty());
    532    /// assert!( (f32::NAN..=5.0).is_empty());
    533    /// ```
    534    ///
    535    /// This method returns `true` after iteration has finished:
    536    ///
    537    /// ```
    538    /// let mut r = 3..=5;
    539    /// for _ in r.by_ref() {}
    540    /// // Precise field values are unspecified here
    541    /// assert!(r.is_empty());
    542    /// ```
    543    #[stable(feature = "range_is_empty", since = "1.47.0")]
    544    #[inline]
    545    pub fn is_empty(&self) -> bool {
    546        self.exhausted || !(self.start <= self.end)
    547    }
    548}
    549
    550/// A range only bounded inclusively above (`..=end`).
    551///
    552/// The `RangeToInclusive` `..=end` contains all values with `x <= end`.
    553/// It cannot serve as an [`Iterator`] because it doesn't have a starting point.
    554///
    555/// # Examples
    556///
    557/// The `..=end` syntax is a `RangeToInclusive`:
    558///
    559/// ```
    560/// assert_eq!((..=5), std::ops::RangeToInclusive{ end: 5 });
    561/// ```
    562///
    563/// It does not have an [`IntoIterator`] implementation, so you can't use it in a
    564/// `for` loop directly. This won't compile:
    565///
    566/// ```compile_fail,E0277
    567/// // error[E0277]: the trait bound `std::ops::RangeToInclusive<{integer}>:
    568/// // std::iter::Iterator` is not satisfied
    569/// for i in ..=5 {
    570///     // ...
    571/// }
    572/// ```
    573///
    574/// When used as a [slicing index], `RangeToInclusive` produces a slice of all
    575/// array elements up to and including the index indicated by `end`.
    576///
    577/// ```
    578/// let arr = [0, 1, 2, 3, 4];
    579/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
    580/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
    581/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]); // This is a `RangeToInclusive`
    582/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
    583/// assert_eq!(arr[1.. 3], [   1, 2      ]);
    584/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
    585/// ```
    586///
    587/// [slicing index]: crate::slice::SliceIndex
    588#[lang = "RangeToInclusive"]
    589#[doc(alias = "..=")]
    590#[derive(Copy, Clone, PartialEq, Eq, Hash)]
    591#[stable(feature = "inclusive_range", since = "1.26.0")]
    592pub struct RangeToInclusive<Idx> {
    593    /// The upper bound of the range (inclusive)
    594    #[stable(feature = "inclusive_range", since = "1.26.0")]
    595    pub end: Idx,
    596}
    597
    598#[stable(feature = "inclusive_range", since = "1.26.0")]
    599impl<Idx: fmt::Debug> fmt::Debug for RangeToInclusive<Idx> {
    600    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
    601        write!(fmt, "..=")?;
    602        self.end.fmt(fmt)?;
    603        Ok(())
    604    }
    605}
    606
    607impl<Idx: PartialOrd<Idx>> RangeToInclusive<Idx> {
    608    /// Returns `true` if `item` is contained in the range.
    609    ///
    610    /// # Examples
    611    ///
    612    /// ```
    613    /// assert!( (..=5).contains(&-1_000_000_000));
    614    /// assert!( (..=5).contains(&5));
    615    /// assert!(!(..=5).contains(&6));
    616    ///
    617    /// assert!( (..=1.0).contains(&1.0));
    618    /// assert!(!(..=1.0).contains(&f32::NAN));
    619    /// assert!(!(..=f32::NAN).contains(&0.5));
    620    /// ```
    621    #[inline]
    622    #[stable(feature = "range_contains", since = "1.35.0")]
    623    pub fn contains<U>(&self, item: &U) -> bool
    624    where
    625        Idx: PartialOrd<U>,
    626        U: ?Sized + PartialOrd<Idx>,
    627    {
    628        <Self as RangeBounds<Idx>>::contains(self, item)
    629    }
    630}
    631
    632// RangeToInclusive<Idx> cannot impl From<RangeTo<Idx>>
    633// because underflow would be possible with (..0).into()
    634
    635/// An endpoint of a range of keys.
    636///
    637/// # Examples
    638///
    639/// `Bound`s are range endpoints:
    640///
    641/// ```
    642/// use std::ops::Bound::*;
    643/// use std::ops::RangeBounds;
    644///
    645/// assert_eq!((..100).start_bound(), Unbounded);
    646/// assert_eq!((1..12).start_bound(), Included(&1));
    647/// assert_eq!((1..12).end_bound(), Excluded(&12));
    648/// ```
    649///
    650/// Using a tuple of `Bound`s as an argument to [`BTreeMap::range`].
    651/// Note that in most cases, it's better to use range syntax (`1..5`) instead.
    652///
    653/// ```
    654/// use std::collections::BTreeMap;
    655/// use std::ops::Bound::{Excluded, Included, Unbounded};
    656///
    657/// let mut map = BTreeMap::new();
    658/// map.insert(3, "a");
    659/// map.insert(5, "b");
    660/// map.insert(8, "c");
    661///
    662/// for (key, value) in map.range((Excluded(3), Included(8))) {
    663///     println!("{key}: {value}");
    664/// }
    665///
    666/// assert_eq!(Some((&3, &"a")), map.range((Unbounded, Included(5))).next());
    667/// ```
    668///
    669/// [`BTreeMap::range`]: ../../std/collections/btree_map/struct.BTreeMap.html#method.range
    670#[stable(feature = "collections_bound", since = "1.17.0")]
    671#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
    672pub enum Bound<T> {
    673    /// An inclusive bound.
    674    #[stable(feature = "collections_bound", since = "1.17.0")]
    675    Included(#[stable(feature = "collections_bound", since = "1.17.0")] T),
    676    /// An exclusive bound.
    677    #[stable(feature = "collections_bound", since = "1.17.0")]
    678    Excluded(#[stable(feature = "collections_bound", since = "1.17.0")] T),
    679    /// An infinite endpoint. Indicates that there is no bound in this direction.
    680    #[stable(feature = "collections_bound", since = "1.17.0")]
    681    Unbounded,
    682}
    683
    684impl<T> Bound<T> {
    685    /// Converts from `&Bound<T>` to `Bound<&T>`.
    686    #[inline]
    687    #[stable(feature = "bound_as_ref_shared", since = "1.65.0")]
    688    pub fn as_ref(&self) -> Bound<&T> {
    689        match *self {
    690            Included(ref x) => Included(x),
    691            Excluded(ref x) => Excluded(x),
    692            Unbounded => Unbounded,
    693        }
    694    }
    695
    696    /// Converts from `&mut Bound<T>` to `Bound<&mut T>`.
    697    #[inline]
    698    #[unstable(feature = "bound_as_ref", issue = "80996")]
    699    pub fn as_mut(&mut self) -> Bound<&mut T> {
    700        match *self {
    701            Included(ref mut x) => Included(x),
    702            Excluded(ref mut x) => Excluded(x),
    703            Unbounded => Unbounded,
    704        }
    705    }
    706
    707    /// Maps a `Bound<T>` to a `Bound<U>` by applying a function to the contained value (including
    708    /// both `Included` and `Excluded`), returning a `Bound` of the same kind.
    709    ///
    710    /// # Examples
    711    ///
    712    /// ```
    713    /// use std::ops::Bound::*;
    714    ///
    715    /// let bound_string = Included("Hello, World!");
    716    ///
    717    /// assert_eq!(bound_string.map(|s| s.len()), Included(13));
    718    /// ```
    719    ///
    720    /// ```
    721    /// use std::ops::Bound;
    722    /// use Bound::*;
    723    ///
    724    /// let unbounded_string: Bound<String> = Unbounded;
    725    ///
    726    /// assert_eq!(unbounded_string.map(|s| s.len()), Unbounded);
    727    /// ```
    728    #[inline]
    729    #[stable(feature = "bound_map", since = "1.77.0")]
    730    pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Bound<U> {
    731        match self {
    732            Unbounded => Unbounded,
    733            Included(x) => Included(f(x)),
    734            Excluded(x) => Excluded(f(x)),
    735        }
    736    }
    737}
    738
    739impl<T: Clone> Bound<&T> {
    740    /// Map a `Bound<&T>` to a `Bound<T>` by cloning the contents of the bound.
    741    ///
    742    /// # Examples
    743    ///
    744    /// ```
    745    /// use std::ops::Bound::*;
    746    /// use std::ops::RangeBounds;
    747    ///
    748    /// assert_eq!((1..12).start_bound(), Included(&1));
    749    /// assert_eq!((1..12).start_bound().cloned(), Included(1));
    750    /// ```
    751    #[must_use = "`self` will be dropped if the result is not used"]
    752    #[stable(feature = "bound_cloned", since = "1.55.0")]
    753    pub fn cloned(self) -> Bound<T> {
    754        match self {
    755            Bound::Unbounded => Bound::Unbounded,
    756            Bound::Included(x) => Bound::Included(x.clone()),
    757            Bound::Excluded(x) => Bound::Excluded(x.clone()),
    758        }
    759    }
    760}
    761
    762/// `RangeBounds` is implemented by Rust's built-in range types, produced
    763/// by range syntax like `..`, `a..`, `..b`, `..=c`, `d..e`, or `f..=g`.
    764#[stable(feature = "collections_range", since = "1.28.0")]
    765#[rustc_diagnostic_item = "RangeBounds"]
    766pub trait RangeBounds<T: ?Sized> {
    767    /// Start index bound.
    768    ///
    769    /// Returns the start value as a `Bound`.
    770    ///
    771    /// # Examples
    772    ///
    773    /// ```
    774    /// use std::ops::Bound::*;
    775    /// use std::ops::RangeBounds;
    776    ///
    777    /// assert_eq!((..10).start_bound(), Unbounded);
    778    /// assert_eq!((3..10).start_bound(), Included(&3));
    779    /// ```
    780    #[stable(feature = "collections_range", since = "1.28.0")]
    781    fn start_bound(&self) -> Bound<&T>;
    782
    783    /// End index bound.
    784    ///
    785    /// Returns the end value as a `Bound`.
    786    ///
    787    /// # Examples
    788    ///
    789    /// ```
    790    /// use std::ops::Bound::*;
    791    /// use std::ops::RangeBounds;
    792    ///
    793    /// assert_eq!((3..).end_bound(), Unbounded);
    794    /// assert_eq!((3..10).end_bound(), Excluded(&10));
    795    /// ```
    796    #[stable(feature = "collections_range", since = "1.28.0")]
    797    fn end_bound(&self) -> Bound<&T>;
    798
    799    /// Returns `true` if `item` is contained in the range.
    800    ///
    801    /// # Examples
    802    ///
    803    /// ```
    804    /// assert!( (3..5).contains(&4));
    805    /// assert!(!(3..5).contains(&2));
    806    ///
    807    /// assert!( (0.0..1.0).contains(&0.5));
    808    /// assert!(!(0.0..1.0).contains(&f32::NAN));
    809    /// assert!(!(0.0..f32::NAN).contains(&0.5));
    810    /// assert!(!(f32::NAN..1.0).contains(&0.5));
    811    #[inline]
    812    #[stable(feature = "range_contains", since = "1.35.0")]
    813    fn contains<U>(&self, item: &U) -> bool
    814    where
    815        T: PartialOrd<U>,
    816        U: ?Sized + PartialOrd<T>,
    817    {
    818        (match self.start_bound() {
    819            Included(start) => start <= item,
    820            Excluded(start) => start < item,
    821            Unbounded => true,
    822        }) && (match self.end_bound() {
    823            Included(end) => item <= end,
    824            Excluded(end) => item < end,
    825            Unbounded => true,
    826        })
    827    }
    828
    829    /// Returns `true` if the range contains no items.
    830    /// One-sided ranges (`RangeFrom`, etc) always return `false`.
    831    ///
    832    /// # Examples
    833    ///
    834    /// ```
    835    /// #![feature(range_bounds_is_empty)]
    836    /// use std::ops::RangeBounds;
    837    ///
    838    /// assert!(!(3..).is_empty());
    839    /// assert!(!(..2).is_empty());
    840    /// assert!(!RangeBounds::is_empty(&(3..5)));
    841    /// assert!( RangeBounds::is_empty(&(3..3)));
    842    /// assert!( RangeBounds::is_empty(&(3..2)));
    843    /// ```
    844    ///
    845    /// The range is empty if either side is incomparable:
    846    ///
    847    /// ```
    848    /// #![feature(range_bounds_is_empty)]
    849    /// use std::ops::RangeBounds;
    850    ///
    851    /// assert!(!RangeBounds::is_empty(&(3.0..5.0)));
    852    /// assert!( RangeBounds::is_empty(&(3.0..f32::NAN)));
    853    /// assert!( RangeBounds::is_empty(&(f32::NAN..5.0)));
    854    /// ```
    855    ///
    856    /// But never empty if either side is unbounded:
    857    ///
    858    /// ```
    859    /// #![feature(range_bounds_is_empty)]
    860    /// use std::ops::RangeBounds;
    861    ///
    862    /// assert!(!(..0).is_empty());
    863    /// assert!(!(i32::MAX..).is_empty());
    864    /// assert!(!RangeBounds::<u8>::is_empty(&(..)));
    865    /// ```
    866    ///
    867    /// `(Excluded(a), Excluded(b))` is only empty if `a >= b`:
    868    ///
    869    /// ```
    870    /// #![feature(range_bounds_is_empty)]
    871    /// use std::ops::Bound::*;
    872    /// use std::ops::RangeBounds;
    873    ///
    874    /// assert!(!(Excluded(1), Excluded(3)).is_empty());
    875    /// assert!(!(Excluded(1), Excluded(2)).is_empty());
    876    /// assert!( (Excluded(1), Excluded(1)).is_empty());
    877    /// assert!( (Excluded(2), Excluded(1)).is_empty());
    878    /// assert!( (Excluded(3), Excluded(1)).is_empty());
    879    /// ```
    880    #[unstable(feature = "range_bounds_is_empty", issue = "137300")]
    881    fn is_empty(&self) -> bool
    882    where
    883        T: PartialOrd,
    884    {
    885        !match (self.start_bound(), self.end_bound()) {
    886            (Unbounded, _) | (_, Unbounded) => true,
    887            (Included(start), Excluded(end))
    888            | (Excluded(start), Included(end))
    889            | (Excluded(start), Excluded(end)) => start < end,
    890            (Included(start), Included(end)) => start <= end,
    891        }
    892    }
    893}
    894
    895/// Used to convert a range into start and end bounds, consuming the
    896/// range by value.
    897///
    898/// `IntoBounds` is implemented by Rust’s built-in range types, produced
    899/// by range syntax like `..`, `a..`, `..b`, `..=c`, `d..e`, or `f..=g`.
    900#[unstable(feature = "range_into_bounds", issue = "136903")]
    901pub trait IntoBounds<T>: RangeBounds<T> {
    902    /// Convert this range into the start and end bounds.
    903    /// Returns `(start_bound, end_bound)`.
    904    ///
    905    /// # Examples
    906    ///
    907    /// ```
    908    /// #![feature(range_into_bounds)]
    909    /// use std::ops::Bound::*;
    910    /// use std::ops::IntoBounds;
    911    ///
    912    /// assert_eq!((0..5).into_bounds(), (Included(0), Excluded(5)));
    913    /// assert_eq!((..=7).into_bounds(), (Unbounded, Included(7)));
    914    /// ```
    915    fn into_bounds(self) -> (Bound<T>, Bound<T>);
    916
    917    /// Compute the intersection of  `self` and `other`.
    918    ///
    919    /// # Examples
    920    ///
    921    /// ```
    922    /// #![feature(range_into_bounds)]
    923    /// use std::ops::Bound::*;
    924    /// use std::ops::IntoBounds;
    925    ///
    926    /// assert_eq!((3..).intersect(..5), (Included(3), Excluded(5)));
    927    /// assert_eq!((-12..387).intersect(0..256), (Included(0), Excluded(256)));
    928    /// assert_eq!((1..5).intersect(..), (Included(1), Excluded(5)));
    929    /// assert_eq!((1..=9).intersect(0..10), (Included(1), Included(9)));
    930    /// assert_eq!((7..=13).intersect(8..13), (Included(8), Excluded(13)));
    931    /// ```
    932    ///
    933    /// Combine with `is_empty` to determine if two ranges overlap.
    934    ///
    935    /// ```
    936    /// #![feature(range_into_bounds)]
    937    /// #![feature(range_bounds_is_empty)]
    938    /// use std::ops::{RangeBounds, IntoBounds};
    939    ///
    940    /// assert!(!(3..).intersect(..5).is_empty());
    941    /// assert!(!(-12..387).intersect(0..256).is_empty());
    942    /// assert!((1..5).intersect(6..).is_empty());
    943    /// ```
    944    fn intersect<R>(self, other: R) -> (Bound<T>, Bound<T>)
    945    where
    946        Self: Sized,
    947        T: Ord,
    948        R: Sized + IntoBounds<T>,
    949    {
    950        let (self_start, self_end) = IntoBounds::into_bounds(self);
    951        let (other_start, other_end) = IntoBounds::into_bounds(other);
    952
    953        let start = match (self_start, other_start) {
    954            (Included(a), Included(b)) => Included(Ord::max(a, b)),
    955            (Excluded(a), Excluded(b)) => Excluded(Ord::max(a, b)),
    956            (Unbounded, Unbounded) => Unbounded,
    957
    958            (x, Unbounded) | (Unbounded, x) => x,
    959
    960            (Included(i), Excluded(e)) | (Excluded(e), Included(i)) => {
    961                if i > e {
    962                    Included(i)
    963                } else {
    964                    Excluded(e)
    965                }
    966            }
    967        };
    968        let end = match (self_end, other_end) {
    969            (Included(a), Included(b)) => Included(Ord::min(a, b)),
    970            (Excluded(a), Excluded(b)) => Excluded(Ord::min(a, b)),
    971            (Unbounded, Unbounded) => Unbounded,
    972
    973            (x, Unbounded) | (Unbounded, x) => x,
    974
    975            (Included(i), Excluded(e)) | (Excluded(e), Included(i)) => {
    976                if i < e {
    977                    Included(i)
    978                } else {
    979                    Excluded(e)
    980                }
    981            }
    982        };
    983
    984        (start, end)
    985    }
    986}
    987
    988use self::Bound::{Excluded, Included, Unbounded};
    989
    990#[stable(feature = "collections_range", since = "1.28.0")]
    991impl<T: ?Sized> RangeBounds<T> for RangeFull {
    992    fn start_bound(&self) -> Bound<&T> {
    993        Unbounded
    994    }
    995    fn end_bound(&self) -> Bound<&T> {
    996        Unbounded
    997    }
    998}
    999
    1000#[unstable(feature = "range_into_bounds", issue = "136903")]
    1001impl<T> IntoBounds<T> for RangeFull {
    1002    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
    1003        (Unbounded, Unbounded)
    1004    }
    1005}
    1006
    1007#[stable(feature = "collections_range", since = "1.28.0")]
    1008impl<T> RangeBounds<T> for RangeFrom<T> {
    1009    fn start_bound(&self) -> Bound<&T> {
    1010        Included(&self.start)
    1011    }
    1012    fn end_bound(&self) -> Bound<&T> {
    1013        Unbounded
    1014    }
    1015}
    1016
    1017#[unstable(feature = "range_into_bounds", issue = "136903")]
    1018impl<T> IntoBounds<T> for RangeFrom<T> {
    1019    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
    1020        (Included(self.start), Unbounded)
    1021    }
    1022}
    1023
    1024#[stable(feature = "collections_range", since = "1.28.0")]
    1025impl<T> RangeBounds<T> for RangeTo<T> {
    1026    fn start_bound(&self) -> Bound<&T> {
    1027        Unbounded
    1028    }
    1029    fn end_bound(&self) -> Bound<&T> {
    1030        Excluded(&self.end)
    1031    }
    1032}
    1033
    1034#[unstable(feature = "range_into_bounds", issue = "136903")]
    1035impl<T> IntoBounds<T> for RangeTo<T> {
    1036    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
    1037        (Unbounded, Excluded(self.end))
    1038    }
    1039}
    1040
    1041#[stable(feature = "collections_range", since = "1.28.0")]
    1042impl<T> RangeBounds<T> for Range<T> {
    1043    fn start_bound(&self) -> Bound<&T> {
    1044        Included(&self.start)
    1045    }
    1046    fn end_bound(&self) -> Bound<&T> {
    1047        Excluded(&self.end)
    1048    }
    1049}
    1050
    1051#[unstable(feature = "range_into_bounds", issue = "136903")]
    1052impl<T> IntoBounds<T> for Range<T> {
    1053    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
    1054        (Included(self.start), Excluded(self.end))
    1055    }
    1056}
    1057
    1058#[stable(feature = "collections_range", since = "1.28.0")]
    1059impl<T> RangeBounds<T> for RangeInclusive<T> {
    1060    fn start_bound(&self) -> Bound<&T> {
    1061        Included(&self.start)
    1062    }
    1063    fn end_bound(&self) -> Bound<&T> {
    1064        if self.exhausted {
    1065            // When the iterator is exhausted, we usually have start == end,
    1066            // but we want the range to appear empty, containing nothing.
    1067            Excluded(&self.end)
    1068        } else {
    1069            Included(&self.end)
    1070        }
    1071    }
    1072}
    1073
    1074#[unstable(feature = "range_into_bounds", issue = "136903")]
    1075impl<T> IntoBounds<T> for RangeInclusive<T> {
    1076    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
    1077        (
    1078            Included(self.start),
    1079            if self.exhausted {
    1080                // When the iterator is exhausted, we usually have start == end,
    1081                // but we want the range to appear empty, containing nothing.
    1082                Excluded(self.end)
    1083            } else {
    1084                Included(self.end)
    1085            },
    1086        )
    1087    }
    1088}
    1089
    1090#[stable(feature = "collections_range", since = "1.28.0")]
    1091impl<T> RangeBounds<T> for RangeToInclusive<T> {
    1092    fn start_bound(&self) -> Bound<&T> {
    1093        Unbounded
    1094    }
    1095    fn end_bound(&self) -> Bound<&T> {
    1096        Included(&self.end)
    1097    }
    1098}
    1099
    1100#[unstable(feature = "range_into_bounds", issue = "136903")]
    1101impl<T> IntoBounds<T> for RangeToInclusive<T> {
    1102    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
    1103        (Unbounded, Included(self.end))
    1104    }
    1105}
    1106
    1107#[stable(feature = "collections_range", since = "1.28.0")]
    1108impl<T> RangeBounds<T> for (Bound<T>, Bound<T>) {
    1109    fn start_bound(&self) -> Bound<&T> {
    1110        match *self {
    1111            (Included(ref start), _) => Included(start),
    1112            (Excluded(ref start), _) => Excluded(start),
    1113            (Unbounded, _) => Unbounded,
    1114        }
    1115    }
    1116
    1117    fn end_bound(&self) -> Bound<&T> {
    1118        match *self {
    1119            (_, Included(ref end)) => Included(end),
    1120            (_, Excluded(ref end)) => Excluded(end),
    1121            (_, Unbounded) => Unbounded,
    1122        }
    1123    }
    1124}
    1125
    1126#[unstable(feature = "range_into_bounds", issue = "136903")]
    1127impl<T> IntoBounds<T> for (Bound<T>, Bound<T>) {
    1128    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
    1129        self
    1130    }
    1131}
    1132
    1133#[stable(feature = "collections_range", since = "1.28.0")]
    1134impl<'a, T: ?Sized + 'a> RangeBounds<T> for (Bound<&'a T>, Bound<&'a T>) {
    1135    fn start_bound(&self) -> Bound<&T> {
    1136        self.0
    1137    }
    1138
    1139    fn end_bound(&self) -> Bound<&T> {
    1140        self.1
    1141    }
    1142}
    1143
    1144// This impl intentionally does not have `T: ?Sized`;
    1145// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
    1146//
    1147/// If you need to use this implementation where `T` is unsized,
    1148/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
    1149/// i.e. replace `start..` with `(Bound::Included(start), Bound::Unbounded)`.
    1150#[stable(feature = "collections_range", since = "1.28.0")]
    1151impl<T> RangeBounds<T> for RangeFrom<&T> {
    1152    fn start_bound(&self) -> Bound<&T> {
    1153        Included(self.start)
    1154    }
    1155    fn end_bound(&self) -> Bound<&T> {
    1156        Unbounded
    1157    }
    1158}
    1159
    1160// This impl intentionally does not have `T: ?Sized`;
    1161// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
    1162//
    1163/// If you need to use this implementation where `T` is unsized,
    1164/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
    1165/// i.e. replace `..end` with `(Bound::Unbounded, Bound::Excluded(end))`.
    1166#[stable(feature = "collections_range", since = "1.28.0")]
    1167impl<T> RangeBounds<T> for RangeTo<&T> {
    1168    fn start_bound(&self) -> Bound<&T> {
    1169        Unbounded
    1170    }
    1171    fn end_bound(&self) -> Bound<&T> {
    1172        Excluded(self.end)
    1173    }
    1174}
    1175
    1176// This impl intentionally does not have `T: ?Sized`;
    1177// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
    1178//
    1179/// If you need to use this implementation where `T` is unsized,
    1180/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
    1181/// i.e. replace `start..end` with `(Bound::Included(start), Bound::Excluded(end))`.
    1182#[stable(feature = "collections_range", since = "1.28.0")]
    1183impl<T> RangeBounds<T> for Range<&T> {
    1184    fn start_bound(&self) -> Bound<&T> {
    1185        Included(self.start)
    1186    }
    1187    fn end_bound(&self) -> Bound<&T> {
    1188        Excluded(self.end)
    1189    }
    1190}
    1191
    1192// This impl intentionally does not have `T: ?Sized`;
    1193// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
    1194//
    1195/// If you need to use this implementation where `T` is unsized,
    1196/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
    1197/// i.e. replace `start..=end` with `(Bound::Included(start), Bound::Included(end))`.
    1198#[stable(feature = "collections_range", since = "1.28.0")]
    1199impl<T> RangeBounds<T> for RangeInclusive<&T> {
    1200    fn start_bound(&self) -> Bound<&T> {
    1201        Included(self.start)
    1202    }
    1203    fn end_bound(&self) -> Bound<&T> {
    1204        Included(self.end)
    1205    }
    1206}
    1207
    1208// This impl intentionally does not have `T: ?Sized`;
    1209// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
    1210//
    1211/// If you need to use this implementation where `T` is unsized,
    1212/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
    1213/// i.e. replace `..=end` with `(Bound::Unbounded, Bound::Included(end))`.
    1214#[stable(feature = "collections_range", since = "1.28.0")]
    1215impl<T> RangeBounds<T> for RangeToInclusive<&T> {
    1216    fn start_bound(&self) -> Bound<&T> {
    1217        Unbounded
    1218    }
    1219    fn end_bound(&self) -> Bound<&T> {
    1220        Included(self.end)
    1221    }
    1222}
    1223
    1224/// An internal helper for `split_off` functions indicating
    1225/// which end a `OneSidedRange` is bounded on.
    1226#[unstable(feature = "one_sided_range", issue = "69780")]
    1227#[allow(missing_debug_implementations)]
    1228pub enum OneSidedRangeBound {
    1229    /// The range is bounded inclusively from below and is unbounded above.
    1230    StartInclusive,
    1231    /// The range is bounded exclusively from above and is unbounded below.
    1232    End,
    1233    /// The range is bounded inclusively from above and is unbounded below.
    1234    EndInclusive,
    1235}
    1236
    1237/// `OneSidedRange` is implemented for built-in range types that are unbounded
    1238/// on one side. For example, `a..`, `..b` and `..=c` implement `OneSidedRange`,
    1239/// but `..`, `d..e`, and `f..=g` do not.
    1240///
    1241/// Types that implement `OneSidedRange<T>` must return `Bound::Unbounded`
    1242/// from one of `RangeBounds::start_bound` or `RangeBounds::end_bound`.
    1243#[unstable(feature = "one_sided_range", issue = "69780")]
    1244pub trait OneSidedRange<T>: RangeBounds<T> {
    1245    /// An internal-only helper function for `split_off` and
    1246    /// `split_off_mut` that returns the bound of the one-sided range.
    1247    fn bound(self) -> (OneSidedRangeBound, T);
    1248}
    1249
    1250#[unstable(feature = "one_sided_range", issue = "69780")]
    1251impl<T> OneSidedRange<T> for RangeTo<T>
    1252where
    1253    Self: RangeBounds<T>,
    1254{
    1255    fn bound(self) -> (OneSidedRangeBound, T) {
    1256        (OneSidedRangeBound::End, self.end)
    1257    }
    1258}
    1259
    1260#[unstable(feature = "one_sided_range", issue = "69780")]
    1261impl<T> OneSidedRange<T> for RangeFrom<T>
    1262where
    1263    Self: RangeBounds<T>,
    1264{
    1265    fn bound(self) -> (OneSidedRangeBound, T) {
    1266        (OneSidedRangeBound::StartInclusive, self.start)
    1267    }
    1268}
    1269
    1270#[unstable(feature = "one_sided_range", issue = "69780")]
    1271impl<T> OneSidedRange<T> for RangeToInclusive<T>
    1272where
    1273    Self: RangeBounds<T>,
    1274{
    1275    fn bound(self) -> (OneSidedRangeBound, T) {
    1276        (OneSidedRangeBound::EndInclusive, self.end)
    1277    }
    1278}