core/ops/
range.rs

1#[cfg(not(feature = "ferrocene_certified"))]
2use crate::fmt;
3#[cfg(not(feature = "ferrocene_certified"))]
4use crate::hash::Hash;
5
6/// An unbounded range (`..`).
7///
8/// `RangeFull` is primarily used as a [slicing index], its shorthand is `..`.
9/// It cannot serve as an [`Iterator`] because it doesn't have a starting point.
10///
11/// # Examples
12///
13/// The `..` syntax is a `RangeFull`:
14///
15/// ```
16/// assert_eq!(.., std::ops::RangeFull);
17/// ```
18///
19/// It does not have an [`IntoIterator`] implementation, so you can't use it in
20/// a `for` loop directly. This won't compile:
21///
22/// ```compile_fail,E0277
23/// for i in .. {
24///     // ...
25/// }
26/// ```
27///
28/// Used as a [slicing index], `RangeFull` produces the full array as a slice.
29///
30/// ```
31/// let arr = [0, 1, 2, 3, 4];
32/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]); // This is the `RangeFull`
33/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
34/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
35/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
36/// assert_eq!(arr[1.. 3], [   1, 2      ]);
37/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
38/// ```
39///
40/// [slicing index]: crate::slice::SliceIndex
41#[lang = "RangeFull"]
42#[doc(alias = "..")]
43#[cfg_attr(not(feature = "ferrocene_certified"), derive(Copy, Clone, Default, PartialEq, Eq, Hash))]
44#[stable(feature = "rust1", since = "1.0.0")]
45pub struct RangeFull;
46
47#[stable(feature = "rust1", since = "1.0.0")]
48#[cfg(not(feature = "ferrocene_certified"))]
49impl fmt::Debug for RangeFull {
50    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
51        write!(fmt, "..")
52    }
53}
54
55/// A (half-open) range bounded inclusively below and exclusively above
56/// (`start..end`).
57///
58/// The range `start..end` contains all values with `start <= x < end`.
59/// It is empty if `start >= end`.
60///
61/// # Examples
62///
63/// The `start..end` syntax is a `Range`:
64///
65/// ```
66/// assert_eq!((3..5), std::ops::Range { start: 3, end: 5 });
67/// assert_eq!(3 + 4 + 5, (3..6).sum());
68/// ```
69///
70/// ```
71/// let arr = [0, 1, 2, 3, 4];
72/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
73/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
74/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
75/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
76/// assert_eq!(arr[1.. 3], [   1, 2      ]); // This is a `Range`
77/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
78/// ```
79#[lang = "Range"]
80#[doc(alias = "..")]
81#[cfg_attr(not(feature = "ferrocene_certified"), derive(Clone, Default, PartialEq, Eq, Hash))] // not Copy -- see #27186
82#[stable(feature = "rust1", since = "1.0.0")]
83pub struct Range<Idx> {
84    /// The lower bound of the range (inclusive).
85    #[stable(feature = "rust1", since = "1.0.0")]
86    pub start: Idx,
87    /// The upper bound of the range (exclusive).
88    #[stable(feature = "rust1", since = "1.0.0")]
89    pub end: Idx,
90}
91
92#[stable(feature = "rust1", since = "1.0.0")]
93#[cfg(not(feature = "ferrocene_certified"))]
94impl<Idx: fmt::Debug> fmt::Debug for Range<Idx> {
95    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
96        self.start.fmt(fmt)?;
97        write!(fmt, "..")?;
98        self.end.fmt(fmt)?;
99        Ok(())
100    }
101}
102
103#[cfg(not(feature = "ferrocene_certified"))]
104impl<Idx: PartialOrd<Idx>> Range<Idx> {
105    /// Returns `true` if `item` is contained in the range.
106    ///
107    /// # Examples
108    ///
109    /// ```
110    /// assert!(!(3..5).contains(&2));
111    /// assert!( (3..5).contains(&3));
112    /// assert!( (3..5).contains(&4));
113    /// assert!(!(3..5).contains(&5));
114    ///
115    /// assert!(!(3..3).contains(&3));
116    /// assert!(!(3..2).contains(&3));
117    ///
118    /// assert!( (0.0..1.0).contains(&0.5));
119    /// assert!(!(0.0..1.0).contains(&f32::NAN));
120    /// assert!(!(0.0..f32::NAN).contains(&0.5));
121    /// assert!(!(f32::NAN..1.0).contains(&0.5));
122    /// ```
123    #[inline]
124    #[stable(feature = "range_contains", since = "1.35.0")]
125    pub fn contains<U>(&self, item: &U) -> bool
126    where
127        Idx: PartialOrd<U>,
128        U: ?Sized + PartialOrd<Idx>,
129    {
130        <Self as RangeBounds<Idx>>::contains(self, item)
131    }
132
133    /// Returns `true` if the range contains no items.
134    ///
135    /// # Examples
136    ///
137    /// ```
138    /// assert!(!(3..5).is_empty());
139    /// assert!( (3..3).is_empty());
140    /// assert!( (3..2).is_empty());
141    /// ```
142    ///
143    /// The range is empty if either side is incomparable:
144    ///
145    /// ```
146    /// assert!(!(3.0..5.0).is_empty());
147    /// assert!( (3.0..f32::NAN).is_empty());
148    /// assert!( (f32::NAN..5.0).is_empty());
149    /// ```
150    #[inline]
151    #[stable(feature = "range_is_empty", since = "1.47.0")]
152    pub fn is_empty(&self) -> bool {
153        !(self.start < self.end)
154    }
155}
156
157/// A range only bounded inclusively below (`start..`).
158///
159/// The `RangeFrom` `start..` contains all values with `x >= start`.
160///
161/// *Note*: Overflow in the [`Iterator`] implementation (when the contained
162/// data type reaches its numerical limit) is allowed to panic, wrap, or
163/// saturate. This behavior is defined by the implementation of the [`Step`]
164/// trait. For primitive integers, this follows the normal rules, and respects
165/// the overflow checks profile (panic in debug, wrap in release). Note also
166/// that overflow happens earlier than you might assume: the overflow happens
167/// in the call to `next` that yields the maximum value, as the range must be
168/// set to a state to yield the next value.
169///
170/// [`Step`]: crate::iter::Step
171///
172/// # Examples
173///
174/// The `start..` syntax is a `RangeFrom`:
175///
176/// ```
177/// assert_eq!((2..), std::ops::RangeFrom { start: 2 });
178/// assert_eq!(2 + 3 + 4, (2..).take(3).sum());
179/// ```
180///
181/// ```
182/// let arr = [0, 1, 2, 3, 4];
183/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
184/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
185/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
186/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]); // This is a `RangeFrom`
187/// assert_eq!(arr[1.. 3], [   1, 2      ]);
188/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
189/// ```
190#[lang = "RangeFrom"]
191#[doc(alias = "..")]
192#[cfg_attr(not(feature = "ferrocene_certified"), derive(Clone, PartialEq, Eq, Hash))] // not Copy -- see #27186
193#[stable(feature = "rust1", since = "1.0.0")]
194pub struct RangeFrom<Idx> {
195    /// The lower bound of the range (inclusive).
196    #[stable(feature = "rust1", since = "1.0.0")]
197    pub start: Idx,
198}
199
200#[stable(feature = "rust1", since = "1.0.0")]
201#[cfg(not(feature = "ferrocene_certified"))]
202impl<Idx: fmt::Debug> fmt::Debug for RangeFrom<Idx> {
203    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
204        self.start.fmt(fmt)?;
205        write!(fmt, "..")?;
206        Ok(())
207    }
208}
209
210#[cfg(not(feature = "ferrocene_certified"))]
211impl<Idx: PartialOrd<Idx>> RangeFrom<Idx> {
212    /// Returns `true` if `item` is contained in the range.
213    ///
214    /// # Examples
215    ///
216    /// ```
217    /// assert!(!(3..).contains(&2));
218    /// assert!( (3..).contains(&3));
219    /// assert!( (3..).contains(&1_000_000_000));
220    ///
221    /// assert!( (0.0..).contains(&0.5));
222    /// assert!(!(0.0..).contains(&f32::NAN));
223    /// assert!(!(f32::NAN..).contains(&0.5));
224    /// ```
225    #[inline]
226    #[stable(feature = "range_contains", since = "1.35.0")]
227    pub fn contains<U>(&self, item: &U) -> bool
228    where
229        Idx: PartialOrd<U>,
230        U: ?Sized + PartialOrd<Idx>,
231    {
232        <Self as RangeBounds<Idx>>::contains(self, item)
233    }
234}
235
236/// A range only bounded exclusively above (`..end`).
237///
238/// The `RangeTo` `..end` contains all values with `x < end`.
239/// It cannot serve as an [`Iterator`] because it doesn't have a starting point.
240///
241/// # Examples
242///
243/// The `..end` syntax is a `RangeTo`:
244///
245/// ```
246/// assert_eq!((..5), std::ops::RangeTo { end: 5 });
247/// ```
248///
249/// It does not have an [`IntoIterator`] implementation, so you can't use it in
250/// a `for` loop directly. This won't compile:
251///
252/// ```compile_fail,E0277
253/// // error[E0277]: the trait bound `std::ops::RangeTo<{integer}>:
254/// // std::iter::Iterator` is not satisfied
255/// for i in ..5 {
256///     // ...
257/// }
258/// ```
259///
260/// When used as a [slicing index], `RangeTo` produces a slice of all array
261/// elements before the index indicated by `end`.
262///
263/// ```
264/// let arr = [0, 1, 2, 3, 4];
265/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
266/// assert_eq!(arr[ .. 3], [0, 1, 2      ]); // This is a `RangeTo`
267/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
268/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
269/// assert_eq!(arr[1.. 3], [   1, 2      ]);
270/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
271/// ```
272///
273/// [slicing index]: crate::slice::SliceIndex
274#[lang = "RangeTo"]
275#[doc(alias = "..")]
276#[cfg_attr(not(feature = "ferrocene_certified"), derive(Copy, Clone, PartialEq, Eq, Hash))]
277#[stable(feature = "rust1", since = "1.0.0")]
278pub struct RangeTo<Idx> {
279    /// The upper bound of the range (exclusive).
280    #[stable(feature = "rust1", since = "1.0.0")]
281    pub end: Idx,
282}
283
284#[stable(feature = "rust1", since = "1.0.0")]
285#[cfg(not(feature = "ferrocene_certified"))]
286impl<Idx: fmt::Debug> fmt::Debug for RangeTo<Idx> {
287    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
288        write!(fmt, "..")?;
289        self.end.fmt(fmt)?;
290        Ok(())
291    }
292}
293
294#[cfg(not(feature = "ferrocene_certified"))]
295impl<Idx: PartialOrd<Idx>> RangeTo<Idx> {
296    /// Returns `true` if `item` is contained in the range.
297    ///
298    /// # Examples
299    ///
300    /// ```
301    /// assert!( (..5).contains(&-1_000_000_000));
302    /// assert!( (..5).contains(&4));
303    /// assert!(!(..5).contains(&5));
304    ///
305    /// assert!( (..1.0).contains(&0.5));
306    /// assert!(!(..1.0).contains(&f32::NAN));
307    /// assert!(!(..f32::NAN).contains(&0.5));
308    /// ```
309    #[inline]
310    #[stable(feature = "range_contains", since = "1.35.0")]
311    pub fn contains<U>(&self, item: &U) -> bool
312    where
313        Idx: PartialOrd<U>,
314        U: ?Sized + PartialOrd<Idx>,
315    {
316        <Self as RangeBounds<Idx>>::contains(self, item)
317    }
318}
319
320/// A range bounded inclusively below and above (`start..=end`).
321///
322/// The `RangeInclusive` `start..=end` contains all values with `x >= start`
323/// and `x <= end`. It is empty unless `start <= end`.
324///
325/// This iterator is [fused], but the specific values of `start` and `end` after
326/// iteration has finished are **unspecified** other than that [`.is_empty()`]
327/// will return `true` once no more values will be produced.
328///
329/// [fused]: crate::iter::FusedIterator
330/// [`.is_empty()`]: RangeInclusive::is_empty
331///
332/// # Examples
333///
334/// The `start..=end` syntax is a `RangeInclusive`:
335///
336/// ```
337/// assert_eq!((3..=5), std::ops::RangeInclusive::new(3, 5));
338/// assert_eq!(3 + 4 + 5, (3..=5).sum());
339/// ```
340///
341/// ```
342/// let arr = [0, 1, 2, 3, 4];
343/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
344/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
345/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]);
346/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
347/// assert_eq!(arr[1.. 3], [   1, 2      ]);
348/// assert_eq!(arr[1..=3], [   1, 2, 3   ]); // This is a `RangeInclusive`
349/// ```
350#[lang = "RangeInclusive"]
351#[doc(alias = "..=")]
352#[cfg_attr(not(feature = "ferrocene_certified"), derive(Clone, PartialEq, Eq, Hash))] // not Copy -- see #27186
353#[stable(feature = "inclusive_range", since = "1.26.0")]
354pub struct RangeInclusive<Idx> {
355    // Note that the fields here are not public to allow changing the
356    // representation in the future; in particular, while we could plausibly
357    // expose start/end, modifying them without changing (future/current)
358    // private fields may lead to incorrect behavior, so we don't want to
359    // support that mode.
360    pub(crate) start: Idx,
361    pub(crate) end: Idx,
362
363    // This field is:
364    //  - `false` upon construction
365    //  - `false` when iteration has yielded an element and the iterator is not exhausted
366    //  - `true` when iteration has been used to exhaust the iterator
367    //
368    // This is required to support PartialEq and Hash without a PartialOrd bound or specialization.
369    pub(crate) exhausted: bool,
370}
371
372impl<Idx> RangeInclusive<Idx> {
373    /// Creates a new inclusive range. Equivalent to writing `start..=end`.
374    ///
375    /// # Examples
376    ///
377    /// ```
378    /// use std::ops::RangeInclusive;
379    ///
380    /// assert_eq!(3..=5, RangeInclusive::new(3, 5));
381    /// ```
382    #[lang = "range_inclusive_new"]
383    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
384    #[inline]
385    #[rustc_promotable]
386    #[rustc_const_stable(feature = "const_range_new", since = "1.32.0")]
387    pub const fn new(start: Idx, end: Idx) -> Self {
388        Self { start, end, exhausted: false }
389    }
390
391    /// Returns the lower bound of the range (inclusive).
392    ///
393    /// When using an inclusive range for iteration, the values of `start()` and
394    /// [`end()`] are unspecified after the iteration ended. To determine
395    /// whether the inclusive range is empty, use the [`is_empty()`] method
396    /// instead of comparing `start() > end()`.
397    ///
398    /// Note: the value returned by this method is unspecified after the range
399    /// has been iterated to exhaustion.
400    ///
401    /// [`end()`]: RangeInclusive::end
402    /// [`is_empty()`]: RangeInclusive::is_empty
403    ///
404    /// # Examples
405    ///
406    /// ```
407    /// assert_eq!((3..=5).start(), &3);
408    /// ```
409    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
410    #[rustc_const_stable(feature = "const_inclusive_range_methods", since = "1.32.0")]
411    #[inline]
412    pub const fn start(&self) -> &Idx {
413        &self.start
414    }
415
416    /// Returns the upper bound of the range (inclusive).
417    ///
418    /// When using an inclusive range for iteration, the values of [`start()`]
419    /// and `end()` are unspecified after the iteration ended. To determine
420    /// whether the inclusive range is empty, use the [`is_empty()`] method
421    /// instead of comparing `start() > end()`.
422    ///
423    /// Note: the value returned by this method is unspecified after the range
424    /// has been iterated to exhaustion.
425    ///
426    /// [`start()`]: RangeInclusive::start
427    /// [`is_empty()`]: RangeInclusive::is_empty
428    ///
429    /// # Examples
430    ///
431    /// ```
432    /// assert_eq!((3..=5).end(), &5);
433    /// ```
434    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
435    #[rustc_const_stable(feature = "const_inclusive_range_methods", since = "1.32.0")]
436    #[inline]
437    pub const fn end(&self) -> &Idx {
438        &self.end
439    }
440
441    /// Destructures the `RangeInclusive` into (lower bound, upper (inclusive) bound).
442    ///
443    /// Note: the value returned by this method is unspecified after the range
444    /// has been iterated to exhaustion.
445    ///
446    /// # Examples
447    ///
448    /// ```
449    /// assert_eq!((3..=5).into_inner(), (3, 5));
450    /// ```
451    #[stable(feature = "inclusive_range_methods", since = "1.27.0")]
452    #[inline]
453    #[rustc_const_unstable(feature = "const_range_bounds", issue = "108082")]
454    #[cfg(not(feature = "ferrocene_certified"))]
455    pub const fn into_inner(self) -> (Idx, Idx) {
456        (self.start, self.end)
457    }
458}
459
460#[cfg(not(feature = "ferrocene_certified"))]
461impl RangeInclusive<usize> {
462    /// Converts to an exclusive `Range` for `SliceIndex` implementations.
463    /// The caller is responsible for dealing with `end == usize::MAX`.
464    #[inline]
465    pub(crate) const fn into_slice_range(self) -> Range<usize> {
466        // If we're not exhausted, we want to simply slice `start..end + 1`.
467        // If we are exhausted, then slicing with `end + 1..end + 1` gives us an
468        // empty range that is still subject to bounds-checks for that endpoint.
469        let exclusive_end = self.end + 1;
470        let start = if self.exhausted { exclusive_end } else { self.start };
471        start..exclusive_end
472    }
473}
474
475#[stable(feature = "inclusive_range", since = "1.26.0")]
476#[cfg(not(feature = "ferrocene_certified"))]
477impl<Idx: fmt::Debug> fmt::Debug for RangeInclusive<Idx> {
478    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
479        self.start.fmt(fmt)?;
480        write!(fmt, "..=")?;
481        self.end.fmt(fmt)?;
482        if self.exhausted {
483            write!(fmt, " (exhausted)")?;
484        }
485        Ok(())
486    }
487}
488
489#[cfg(not(feature = "ferrocene_certified"))]
490impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
491    /// Returns `true` if `item` is contained in the range.
492    ///
493    /// # Examples
494    ///
495    /// ```
496    /// assert!(!(3..=5).contains(&2));
497    /// assert!( (3..=5).contains(&3));
498    /// assert!( (3..=5).contains(&4));
499    /// assert!( (3..=5).contains(&5));
500    /// assert!(!(3..=5).contains(&6));
501    ///
502    /// assert!( (3..=3).contains(&3));
503    /// assert!(!(3..=2).contains(&3));
504    ///
505    /// assert!( (0.0..=1.0).contains(&1.0));
506    /// assert!(!(0.0..=1.0).contains(&f32::NAN));
507    /// assert!(!(0.0..=f32::NAN).contains(&0.0));
508    /// assert!(!(f32::NAN..=1.0).contains(&1.0));
509    /// ```
510    ///
511    /// This method always returns `false` after iteration has finished:
512    ///
513    /// ```
514    /// let mut r = 3..=5;
515    /// assert!(r.contains(&3) && r.contains(&5));
516    /// for _ in r.by_ref() {}
517    /// // Precise field values are unspecified here
518    /// assert!(!r.contains(&3) && !r.contains(&5));
519    /// ```
520    #[inline]
521    #[stable(feature = "range_contains", since = "1.35.0")]
522    pub fn contains<U>(&self, item: &U) -> bool
523    where
524        Idx: PartialOrd<U>,
525        U: ?Sized + PartialOrd<Idx>,
526    {
527        <Self as RangeBounds<Idx>>::contains(self, item)
528    }
529
530    /// Returns `true` if the range contains no items.
531    ///
532    /// # Examples
533    ///
534    /// ```
535    /// assert!(!(3..=5).is_empty());
536    /// assert!(!(3..=3).is_empty());
537    /// assert!( (3..=2).is_empty());
538    /// ```
539    ///
540    /// The range is empty if either side is incomparable:
541    ///
542    /// ```
543    /// assert!(!(3.0..=5.0).is_empty());
544    /// assert!( (3.0..=f32::NAN).is_empty());
545    /// assert!( (f32::NAN..=5.0).is_empty());
546    /// ```
547    ///
548    /// This method returns `true` after iteration has finished:
549    ///
550    /// ```
551    /// let mut r = 3..=5;
552    /// for _ in r.by_ref() {}
553    /// // Precise field values are unspecified here
554    /// assert!(r.is_empty());
555    /// ```
556    #[stable(feature = "range_is_empty", since = "1.47.0")]
557    #[inline]
558    pub fn is_empty(&self) -> bool {
559        self.exhausted || !(self.start <= self.end)
560    }
561}
562
563/// A range only bounded inclusively above (`..=end`).
564///
565/// The `RangeToInclusive` `..=end` contains all values with `x <= end`.
566/// It cannot serve as an [`Iterator`] because it doesn't have a starting point.
567///
568/// # Examples
569///
570/// The `..=end` syntax is a `RangeToInclusive`:
571///
572/// ```
573/// assert_eq!((..=5), std::ops::RangeToInclusive{ end: 5 });
574/// ```
575///
576/// It does not have an [`IntoIterator`] implementation, so you can't use it in a
577/// `for` loop directly. This won't compile:
578///
579/// ```compile_fail,E0277
580/// // error[E0277]: the trait bound `std::ops::RangeToInclusive<{integer}>:
581/// // std::iter::Iterator` is not satisfied
582/// for i in ..=5 {
583///     // ...
584/// }
585/// ```
586///
587/// When used as a [slicing index], `RangeToInclusive` produces a slice of all
588/// array elements up to and including the index indicated by `end`.
589///
590/// ```
591/// let arr = [0, 1, 2, 3, 4];
592/// assert_eq!(arr[ ..  ], [0, 1, 2, 3, 4]);
593/// assert_eq!(arr[ .. 3], [0, 1, 2      ]);
594/// assert_eq!(arr[ ..=3], [0, 1, 2, 3   ]); // This is a `RangeToInclusive`
595/// assert_eq!(arr[1..  ], [   1, 2, 3, 4]);
596/// assert_eq!(arr[1.. 3], [   1, 2      ]);
597/// assert_eq!(arr[1..=3], [   1, 2, 3   ]);
598/// ```
599///
600/// [slicing index]: crate::slice::SliceIndex
601#[lang = "RangeToInclusive"]
602#[doc(alias = "..=")]
603#[cfg_attr(not(feature = "ferrocene_certified"), derive(Copy, Clone, PartialEq, Eq, Hash))]
604#[stable(feature = "inclusive_range", since = "1.26.0")]
605pub struct RangeToInclusive<Idx> {
606    /// The upper bound of the range (inclusive)
607    #[stable(feature = "inclusive_range", since = "1.26.0")]
608    pub end: Idx,
609}
610
611#[stable(feature = "inclusive_range", since = "1.26.0")]
612#[cfg(not(feature = "ferrocene_certified"))]
613impl<Idx: fmt::Debug> fmt::Debug for RangeToInclusive<Idx> {
614    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
615        write!(fmt, "..=")?;
616        self.end.fmt(fmt)?;
617        Ok(())
618    }
619}
620
621#[cfg(not(feature = "ferrocene_certified"))]
622impl<Idx: PartialOrd<Idx>> RangeToInclusive<Idx> {
623    /// Returns `true` if `item` is contained in the range.
624    ///
625    /// # Examples
626    ///
627    /// ```
628    /// assert!( (..=5).contains(&-1_000_000_000));
629    /// assert!( (..=5).contains(&5));
630    /// assert!(!(..=5).contains(&6));
631    ///
632    /// assert!( (..=1.0).contains(&1.0));
633    /// assert!(!(..=1.0).contains(&f32::NAN));
634    /// assert!(!(..=f32::NAN).contains(&0.5));
635    /// ```
636    #[inline]
637    #[stable(feature = "range_contains", since = "1.35.0")]
638    pub fn contains<U>(&self, item: &U) -> bool
639    where
640        Idx: PartialOrd<U>,
641        U: ?Sized + PartialOrd<Idx>,
642    {
643        <Self as RangeBounds<Idx>>::contains(self, item)
644    }
645}
646
647// RangeToInclusive<Idx> cannot impl From<RangeTo<Idx>>
648// because underflow would be possible with (..0).into()
649
650/// An endpoint of a range of keys.
651///
652/// # Examples
653///
654/// `Bound`s are range endpoints:
655///
656/// ```
657/// use std::ops::Bound::*;
658/// use std::ops::RangeBounds;
659///
660/// assert_eq!((..100).start_bound(), Unbounded);
661/// assert_eq!((1..12).start_bound(), Included(&1));
662/// assert_eq!((1..12).end_bound(), Excluded(&12));
663/// ```
664///
665/// Using a tuple of `Bound`s as an argument to [`BTreeMap::range`].
666/// Note that in most cases, it's better to use range syntax (`1..5`) instead.
667///
668/// ```
669/// use std::collections::BTreeMap;
670/// use std::ops::Bound::{Excluded, Included, Unbounded};
671///
672/// let mut map = BTreeMap::new();
673/// map.insert(3, "a");
674/// map.insert(5, "b");
675/// map.insert(8, "c");
676///
677/// for (key, value) in map.range((Excluded(3), Included(8))) {
678///     println!("{key}: {value}");
679/// }
680///
681/// assert_eq!(Some((&3, &"a")), map.range((Unbounded, Included(5))).next());
682/// ```
683///
684/// [`BTreeMap::range`]: ../../std/collections/btree_map/struct.BTreeMap.html#method.range
685#[stable(feature = "collections_bound", since = "1.17.0")]
686#[cfg_attr(not(feature = "ferrocene_certified"), derive(Clone, Copy, Debug, Hash, PartialEq, Eq))]
687pub enum Bound<T> {
688    /// An inclusive bound.
689    #[stable(feature = "collections_bound", since = "1.17.0")]
690    Included(#[stable(feature = "collections_bound", since = "1.17.0")] T),
691    /// An exclusive bound.
692    #[stable(feature = "collections_bound", since = "1.17.0")]
693    Excluded(#[stable(feature = "collections_bound", since = "1.17.0")] T),
694    /// An infinite endpoint. Indicates that there is no bound in this direction.
695    #[stable(feature = "collections_bound", since = "1.17.0")]
696    Unbounded,
697}
698
699impl<T> Bound<T> {
700    /// Converts from `&Bound<T>` to `Bound<&T>`.
701    #[inline]
702    #[stable(feature = "bound_as_ref_shared", since = "1.65.0")]
703    pub fn as_ref(&self) -> Bound<&T> {
704        match *self {
705            Included(ref x) => Included(x),
706            Excluded(ref x) => Excluded(x),
707            Unbounded => Unbounded,
708        }
709    }
710
711    /// Converts from `&mut Bound<T>` to `Bound<&mut T>`.
712    #[inline]
713    #[unstable(feature = "bound_as_ref", issue = "80996")]
714    pub fn as_mut(&mut self) -> Bound<&mut T> {
715        match *self {
716            Included(ref mut x) => Included(x),
717            Excluded(ref mut x) => Excluded(x),
718            Unbounded => Unbounded,
719        }
720    }
721
722    /// Maps a `Bound<T>` to a `Bound<U>` by applying a function to the contained value (including
723    /// both `Included` and `Excluded`), returning a `Bound` of the same kind.
724    ///
725    /// # Examples
726    ///
727    /// ```
728    /// use std::ops::Bound::*;
729    ///
730    /// let bound_string = Included("Hello, World!");
731    ///
732    /// assert_eq!(bound_string.map(|s| s.len()), Included(13));
733    /// ```
734    ///
735    /// ```
736    /// use std::ops::Bound;
737    /// use Bound::*;
738    ///
739    /// let unbounded_string: Bound<String> = Unbounded;
740    ///
741    /// assert_eq!(unbounded_string.map(|s| s.len()), Unbounded);
742    /// ```
743    #[inline]
744    #[stable(feature = "bound_map", since = "1.77.0")]
745    pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Bound<U> {
746        match self {
747            Unbounded => Unbounded,
748            Included(x) => Included(f(x)),
749            Excluded(x) => Excluded(f(x)),
750        }
751    }
752}
753
754impl<T: Clone> Bound<&T> {
755    /// Map a `Bound<&T>` to a `Bound<T>` by cloning the contents of the bound.
756    ///
757    /// # Examples
758    ///
759    /// ```
760    /// use std::ops::Bound::*;
761    /// use std::ops::RangeBounds;
762    ///
763    /// assert_eq!((1..12).start_bound(), Included(&1));
764    /// assert_eq!((1..12).start_bound().cloned(), Included(1));
765    /// ```
766    #[must_use = "`self` will be dropped if the result is not used"]
767    #[stable(feature = "bound_cloned", since = "1.55.0")]
768    pub fn cloned(self) -> Bound<T> {
769        match self {
770            Bound::Unbounded => Bound::Unbounded,
771            Bound::Included(x) => Bound::Included(x.clone()),
772            Bound::Excluded(x) => Bound::Excluded(x.clone()),
773        }
774    }
775}
776
777/// `RangeBounds` is implemented by Rust's built-in range types, produced
778/// by range syntax like `..`, `a..`, `..b`, `..=c`, `d..e`, or `f..=g`.
779#[stable(feature = "collections_range", since = "1.28.0")]
780#[rustc_diagnostic_item = "RangeBounds"]
781pub trait RangeBounds<T: ?Sized> {
782    /// Start index bound.
783    ///
784    /// Returns the start value as a `Bound`.
785    ///
786    /// # Examples
787    ///
788    /// ```
789    /// use std::ops::Bound::*;
790    /// use std::ops::RangeBounds;
791    ///
792    /// assert_eq!((..10).start_bound(), Unbounded);
793    /// assert_eq!((3..10).start_bound(), Included(&3));
794    /// ```
795    #[stable(feature = "collections_range", since = "1.28.0")]
796    fn start_bound(&self) -> Bound<&T>;
797
798    /// End index bound.
799    ///
800    /// Returns the end value as a `Bound`.
801    ///
802    /// # Examples
803    ///
804    /// ```
805    /// use std::ops::Bound::*;
806    /// use std::ops::RangeBounds;
807    ///
808    /// assert_eq!((3..).end_bound(), Unbounded);
809    /// assert_eq!((3..10).end_bound(), Excluded(&10));
810    /// ```
811    #[stable(feature = "collections_range", since = "1.28.0")]
812    fn end_bound(&self) -> Bound<&T>;
813
814    /// Returns `true` if `item` is contained in the range.
815    ///
816    /// # Examples
817    ///
818    /// ```
819    /// assert!( (3..5).contains(&4));
820    /// assert!(!(3..5).contains(&2));
821    ///
822    /// assert!( (0.0..1.0).contains(&0.5));
823    /// assert!(!(0.0..1.0).contains(&f32::NAN));
824    /// assert!(!(0.0..f32::NAN).contains(&0.5));
825    /// assert!(!(f32::NAN..1.0).contains(&0.5));
826    #[inline]
827    #[stable(feature = "range_contains", since = "1.35.0")]
828    #[cfg(not(feature = "ferrocene_certified"))]
829    fn contains<U>(&self, item: &U) -> bool
830    where
831        T: PartialOrd<U>,
832        U: ?Sized + PartialOrd<T>,
833    {
834        (match self.start_bound() {
835            Included(start) => start <= item,
836            Excluded(start) => start < item,
837            Unbounded => true,
838        }) && (match self.end_bound() {
839            Included(end) => item <= end,
840            Excluded(end) => item < end,
841            Unbounded => true,
842        })
843    }
844
845    /// Returns `true` if the range contains no items.
846    /// One-sided ranges (`RangeFrom`, etc) always return `false`.
847    ///
848    /// # Examples
849    ///
850    /// ```
851    /// #![feature(range_bounds_is_empty)]
852    /// use std::ops::RangeBounds;
853    ///
854    /// assert!(!(3..).is_empty());
855    /// assert!(!(..2).is_empty());
856    /// assert!(!RangeBounds::is_empty(&(3..5)));
857    /// assert!( RangeBounds::is_empty(&(3..3)));
858    /// assert!( RangeBounds::is_empty(&(3..2)));
859    /// ```
860    ///
861    /// The range is empty if either side is incomparable:
862    ///
863    /// ```
864    /// #![feature(range_bounds_is_empty)]
865    /// use std::ops::RangeBounds;
866    ///
867    /// assert!(!RangeBounds::is_empty(&(3.0..5.0)));
868    /// assert!( RangeBounds::is_empty(&(3.0..f32::NAN)));
869    /// assert!( RangeBounds::is_empty(&(f32::NAN..5.0)));
870    /// ```
871    ///
872    /// But never empty if either side is unbounded:
873    ///
874    /// ```
875    /// #![feature(range_bounds_is_empty)]
876    /// use std::ops::RangeBounds;
877    ///
878    /// assert!(!(..0).is_empty());
879    /// assert!(!(i32::MAX..).is_empty());
880    /// assert!(!RangeBounds::<u8>::is_empty(&(..)));
881    /// ```
882    ///
883    /// `(Excluded(a), Excluded(b))` is only empty if `a >= b`:
884    ///
885    /// ```
886    /// #![feature(range_bounds_is_empty)]
887    /// use std::ops::Bound::*;
888    /// use std::ops::RangeBounds;
889    ///
890    /// assert!(!(Excluded(1), Excluded(3)).is_empty());
891    /// assert!(!(Excluded(1), Excluded(2)).is_empty());
892    /// assert!( (Excluded(1), Excluded(1)).is_empty());
893    /// assert!( (Excluded(2), Excluded(1)).is_empty());
894    /// assert!( (Excluded(3), Excluded(1)).is_empty());
895    /// ```
896    #[unstable(feature = "range_bounds_is_empty", issue = "137300")]
897    #[cfg(not(feature = "ferrocene_certified"))]
898    fn is_empty(&self) -> bool
899    where
900        T: PartialOrd,
901    {
902        !match (self.start_bound(), self.end_bound()) {
903            (Unbounded, _) | (_, Unbounded) => true,
904            (Included(start), Excluded(end))
905            | (Excluded(start), Included(end))
906            | (Excluded(start), Excluded(end)) => start < end,
907            (Included(start), Included(end)) => start <= end,
908        }
909    }
910}
911
912/// Used to convert a range into start and end bounds, consuming the
913/// range by value.
914///
915/// `IntoBounds` is implemented by Rust’s built-in range types, produced
916/// by range syntax like `..`, `a..`, `..b`, `..=c`, `d..e`, or `f..=g`.
917#[unstable(feature = "range_into_bounds", issue = "136903")]
918pub trait IntoBounds<T>: RangeBounds<T> {
919    /// Convert this range into the start and end bounds.
920    /// Returns `(start_bound, end_bound)`.
921    ///
922    /// # Examples
923    ///
924    /// ```
925    /// #![feature(range_into_bounds)]
926    /// use std::ops::Bound::*;
927    /// use std::ops::IntoBounds;
928    ///
929    /// assert_eq!((0..5).into_bounds(), (Included(0), Excluded(5)));
930    /// assert_eq!((..=7).into_bounds(), (Unbounded, Included(7)));
931    /// ```
932    fn into_bounds(self) -> (Bound<T>, Bound<T>);
933
934    /// Compute the intersection of  `self` and `other`.
935    ///
936    /// # Examples
937    ///
938    /// ```
939    /// #![feature(range_into_bounds)]
940    /// use std::ops::Bound::*;
941    /// use std::ops::IntoBounds;
942    ///
943    /// assert_eq!((3..).intersect(..5), (Included(3), Excluded(5)));
944    /// assert_eq!((-12..387).intersect(0..256), (Included(0), Excluded(256)));
945    /// assert_eq!((1..5).intersect(..), (Included(1), Excluded(5)));
946    /// assert_eq!((1..=9).intersect(0..10), (Included(1), Included(9)));
947    /// assert_eq!((7..=13).intersect(8..13), (Included(8), Excluded(13)));
948    /// ```
949    ///
950    /// Combine with `is_empty` to determine if two ranges overlap.
951    ///
952    /// ```
953    /// #![feature(range_into_bounds)]
954    /// #![feature(range_bounds_is_empty)]
955    /// use std::ops::{RangeBounds, IntoBounds};
956    ///
957    /// assert!(!(3..).intersect(..5).is_empty());
958    /// assert!(!(-12..387).intersect(0..256).is_empty());
959    /// assert!((1..5).intersect(6..).is_empty());
960    /// ```
961    #[cfg(not(feature = "ferrocene_certified"))]
962    fn intersect<R>(self, other: R) -> (Bound<T>, Bound<T>)
963    where
964        Self: Sized,
965        T: Ord,
966        R: Sized + IntoBounds<T>,
967    {
968        let (self_start, self_end) = IntoBounds::into_bounds(self);
969        let (other_start, other_end) = IntoBounds::into_bounds(other);
970
971        let start = match (self_start, other_start) {
972            (Included(a), Included(b)) => Included(Ord::max(a, b)),
973            (Excluded(a), Excluded(b)) => Excluded(Ord::max(a, b)),
974            (Unbounded, Unbounded) => Unbounded,
975
976            (x, Unbounded) | (Unbounded, x) => x,
977
978            (Included(i), Excluded(e)) | (Excluded(e), Included(i)) => {
979                if i > e {
980                    Included(i)
981                } else {
982                    Excluded(e)
983                }
984            }
985        };
986        let end = match (self_end, other_end) {
987            (Included(a), Included(b)) => Included(Ord::min(a, b)),
988            (Excluded(a), Excluded(b)) => Excluded(Ord::min(a, b)),
989            (Unbounded, Unbounded) => Unbounded,
990
991            (x, Unbounded) | (Unbounded, x) => x,
992
993            (Included(i), Excluded(e)) | (Excluded(e), Included(i)) => {
994                if i < e {
995                    Included(i)
996                } else {
997                    Excluded(e)
998                }
999            }
1000        };
1001
1002        (start, end)
1003    }
1004}
1005
1006use self::Bound::{Excluded, Included, Unbounded};
1007
1008#[stable(feature = "collections_range", since = "1.28.0")]
1009impl<T: ?Sized> RangeBounds<T> for RangeFull {
1010    fn start_bound(&self) -> Bound<&T> {
1011        Unbounded
1012    }
1013    fn end_bound(&self) -> Bound<&T> {
1014        Unbounded
1015    }
1016}
1017
1018#[unstable(feature = "range_into_bounds", issue = "136903")]
1019impl<T> IntoBounds<T> for RangeFull {
1020    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
1021        (Unbounded, Unbounded)
1022    }
1023}
1024
1025#[stable(feature = "collections_range", since = "1.28.0")]
1026impl<T> RangeBounds<T> for RangeFrom<T> {
1027    fn start_bound(&self) -> Bound<&T> {
1028        Included(&self.start)
1029    }
1030    fn end_bound(&self) -> Bound<&T> {
1031        Unbounded
1032    }
1033}
1034
1035#[unstable(feature = "range_into_bounds", issue = "136903")]
1036impl<T> IntoBounds<T> for RangeFrom<T> {
1037    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
1038        (Included(self.start), Unbounded)
1039    }
1040}
1041
1042#[stable(feature = "collections_range", since = "1.28.0")]
1043impl<T> RangeBounds<T> for RangeTo<T> {
1044    fn start_bound(&self) -> Bound<&T> {
1045        Unbounded
1046    }
1047    fn end_bound(&self) -> Bound<&T> {
1048        Excluded(&self.end)
1049    }
1050}
1051
1052#[unstable(feature = "range_into_bounds", issue = "136903")]
1053impl<T> IntoBounds<T> for RangeTo<T> {
1054    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
1055        (Unbounded, Excluded(self.end))
1056    }
1057}
1058
1059#[stable(feature = "collections_range", since = "1.28.0")]
1060impl<T> RangeBounds<T> for Range<T> {
1061    fn start_bound(&self) -> Bound<&T> {
1062        Included(&self.start)
1063    }
1064    fn end_bound(&self) -> Bound<&T> {
1065        Excluded(&self.end)
1066    }
1067}
1068
1069#[unstable(feature = "range_into_bounds", issue = "136903")]
1070impl<T> IntoBounds<T> for Range<T> {
1071    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
1072        (Included(self.start), Excluded(self.end))
1073    }
1074}
1075
1076#[stable(feature = "collections_range", since = "1.28.0")]
1077impl<T> RangeBounds<T> for RangeInclusive<T> {
1078    fn start_bound(&self) -> Bound<&T> {
1079        Included(&self.start)
1080    }
1081    fn end_bound(&self) -> Bound<&T> {
1082        if self.exhausted {
1083            // When the iterator is exhausted, we usually have start == end,
1084            // but we want the range to appear empty, containing nothing.
1085            Excluded(&self.end)
1086        } else {
1087            Included(&self.end)
1088        }
1089    }
1090}
1091
1092#[unstable(feature = "range_into_bounds", issue = "136903")]
1093impl<T> IntoBounds<T> for RangeInclusive<T> {
1094    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
1095        (
1096            Included(self.start),
1097            if self.exhausted {
1098                // When the iterator is exhausted, we usually have start == end,
1099                // but we want the range to appear empty, containing nothing.
1100                Excluded(self.end)
1101            } else {
1102                Included(self.end)
1103            },
1104        )
1105    }
1106}
1107
1108#[stable(feature = "collections_range", since = "1.28.0")]
1109impl<T> RangeBounds<T> for RangeToInclusive<T> {
1110    fn start_bound(&self) -> Bound<&T> {
1111        Unbounded
1112    }
1113    fn end_bound(&self) -> Bound<&T> {
1114        Included(&self.end)
1115    }
1116}
1117
1118#[unstable(feature = "range_into_bounds", issue = "136903")]
1119impl<T> IntoBounds<T> for RangeToInclusive<T> {
1120    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
1121        (Unbounded, Included(self.end))
1122    }
1123}
1124
1125#[stable(feature = "collections_range", since = "1.28.0")]
1126impl<T> RangeBounds<T> for (Bound<T>, Bound<T>) {
1127    fn start_bound(&self) -> Bound<&T> {
1128        match *self {
1129            (Included(ref start), _) => Included(start),
1130            (Excluded(ref start), _) => Excluded(start),
1131            (Unbounded, _) => Unbounded,
1132        }
1133    }
1134
1135    fn end_bound(&self) -> Bound<&T> {
1136        match *self {
1137            (_, Included(ref end)) => Included(end),
1138            (_, Excluded(ref end)) => Excluded(end),
1139            (_, Unbounded) => Unbounded,
1140        }
1141    }
1142}
1143
1144#[unstable(feature = "range_into_bounds", issue = "136903")]
1145impl<T> IntoBounds<T> for (Bound<T>, Bound<T>) {
1146    fn into_bounds(self) -> (Bound<T>, Bound<T>) {
1147        self
1148    }
1149}
1150
1151#[stable(feature = "collections_range", since = "1.28.0")]
1152#[cfg(not(feature = "ferrocene_certified"))]
1153impl<'a, T: ?Sized + 'a> RangeBounds<T> for (Bound<&'a T>, Bound<&'a T>) {
1154    fn start_bound(&self) -> Bound<&T> {
1155        self.0
1156    }
1157
1158    fn end_bound(&self) -> Bound<&T> {
1159        self.1
1160    }
1161}
1162
1163// This impl intentionally does not have `T: ?Sized`;
1164// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
1165//
1166/// If you need to use this implementation where `T` is unsized,
1167/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
1168/// i.e. replace `start..` with `(Bound::Included(start), Bound::Unbounded)`.
1169#[stable(feature = "collections_range", since = "1.28.0")]
1170impl<T> RangeBounds<T> for RangeFrom<&T> {
1171    fn start_bound(&self) -> Bound<&T> {
1172        Included(self.start)
1173    }
1174    fn end_bound(&self) -> Bound<&T> {
1175        Unbounded
1176    }
1177}
1178
1179// This impl intentionally does not have `T: ?Sized`;
1180// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
1181//
1182/// If you need to use this implementation where `T` is unsized,
1183/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
1184/// i.e. replace `..end` with `(Bound::Unbounded, Bound::Excluded(end))`.
1185#[stable(feature = "collections_range", since = "1.28.0")]
1186impl<T> RangeBounds<T> for RangeTo<&T> {
1187    fn start_bound(&self) -> Bound<&T> {
1188        Unbounded
1189    }
1190    fn end_bound(&self) -> Bound<&T> {
1191        Excluded(self.end)
1192    }
1193}
1194
1195// This impl intentionally does not have `T: ?Sized`;
1196// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
1197//
1198/// If you need to use this implementation where `T` is unsized,
1199/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
1200/// i.e. replace `start..end` with `(Bound::Included(start), Bound::Excluded(end))`.
1201#[stable(feature = "collections_range", since = "1.28.0")]
1202impl<T> RangeBounds<T> for Range<&T> {
1203    fn start_bound(&self) -> Bound<&T> {
1204        Included(self.start)
1205    }
1206    fn end_bound(&self) -> Bound<&T> {
1207        Excluded(self.end)
1208    }
1209}
1210
1211// This impl intentionally does not have `T: ?Sized`;
1212// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
1213//
1214/// If you need to use this implementation where `T` is unsized,
1215/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
1216/// i.e. replace `start..=end` with `(Bound::Included(start), Bound::Included(end))`.
1217#[stable(feature = "collections_range", since = "1.28.0")]
1218impl<T> RangeBounds<T> for RangeInclusive<&T> {
1219    fn start_bound(&self) -> Bound<&T> {
1220        Included(self.start)
1221    }
1222    fn end_bound(&self) -> Bound<&T> {
1223        Included(self.end)
1224    }
1225}
1226
1227// This impl intentionally does not have `T: ?Sized`;
1228// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
1229//
1230/// If you need to use this implementation where `T` is unsized,
1231/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
1232/// i.e. replace `..=end` with `(Bound::Unbounded, Bound::Included(end))`.
1233#[stable(feature = "collections_range", since = "1.28.0")]
1234impl<T> RangeBounds<T> for RangeToInclusive<&T> {
1235    fn start_bound(&self) -> Bound<&T> {
1236        Unbounded
1237    }
1238    fn end_bound(&self) -> Bound<&T> {
1239        Included(self.end)
1240    }
1241}
1242
1243/// An internal helper for `split_off` functions indicating
1244/// which end a `OneSidedRange` is bounded on.
1245#[unstable(feature = "one_sided_range", issue = "69780")]
1246#[allow(missing_debug_implementations)]
1247pub enum OneSidedRangeBound {
1248    /// The range is bounded inclusively from below and is unbounded above.
1249    StartInclusive,
1250    /// The range is bounded exclusively from above and is unbounded below.
1251    End,
1252    /// The range is bounded inclusively from above and is unbounded below.
1253    EndInclusive,
1254}
1255
1256/// `OneSidedRange` is implemented for built-in range types that are unbounded
1257/// on one side. For example, `a..`, `..b` and `..=c` implement `OneSidedRange`,
1258/// but `..`, `d..e`, and `f..=g` do not.
1259///
1260/// Types that implement `OneSidedRange<T>` must return `Bound::Unbounded`
1261/// from one of `RangeBounds::start_bound` or `RangeBounds::end_bound`.
1262#[unstable(feature = "one_sided_range", issue = "69780")]
1263pub trait OneSidedRange<T>: RangeBounds<T> {
1264    /// An internal-only helper function for `split_off` and
1265    /// `split_off_mut` that returns the bound of the one-sided range.
1266    fn bound(self) -> (OneSidedRangeBound, T);
1267}
1268
1269#[unstable(feature = "one_sided_range", issue = "69780")]
1270impl<T> OneSidedRange<T> for RangeTo<T>
1271where
1272    Self: RangeBounds<T>,
1273{
1274    fn bound(self) -> (OneSidedRangeBound, T) {
1275        (OneSidedRangeBound::End, self.end)
1276    }
1277}
1278
1279#[unstable(feature = "one_sided_range", issue = "69780")]
1280impl<T> OneSidedRange<T> for RangeFrom<T>
1281where
1282    Self: RangeBounds<T>,
1283{
1284    fn bound(self) -> (OneSidedRangeBound, T) {
1285        (OneSidedRangeBound::StartInclusive, self.start)
1286    }
1287}
1288
1289#[unstable(feature = "one_sided_range", issue = "69780")]
1290impl<T> OneSidedRange<T> for RangeToInclusive<T>
1291where
1292    Self: RangeBounds<T>,
1293{
1294    fn bound(self) -> (OneSidedRangeBound, T) {
1295        (OneSidedRangeBound::EndInclusive, self.end)
1296    }
1297}