1 //! Functionality for ordering and comparison.
3 //! This module contains various tools for ordering and comparing values. In
6 //! * [`Eq`] and [`PartialEq`] are traits that allow you to define total and
7 //! partial equality between values, respectively. Implementing them overloads
8 //! the `==` and `!=` operators.
9 //! * [`Ord`] and [`PartialOrd`] are traits that allow you to define total and
10 //! partial orderings between values, respectively. Implementing them overloads
11 //! the `<`, `<=`, `>`, and `>=` operators.
12 //! * [`Ordering`] is an enum returned by the main functions of [`Ord`] and
13 //! [`PartialOrd`], and describes an ordering.
14 //! * [`Reverse`] is a struct that allows you to easily reverse an ordering.
15 //! * [`max`] and [`min`] are functions that build off of [`Ord`] and allow you
16 //! to find the maximum or minimum of two values.
18 //! For more details, see the respective documentation of each item in the list.
23 #![stable(feature = "rust1", since = "1.0.0")]
25 use self::Ordering::*;
27 /// Trait for equality comparisons which are [partial equivalence
28 /// relations](https://en.wikipedia.org/wiki/Partial_equivalence_relation).
30 /// This trait allows for partial equality, for types that do not have a full
31 /// equivalence relation. For example, in floating point numbers `NaN != NaN`,
32 /// so floating point types implement `PartialEq` but not [`Eq`].
34 /// Formally, the equality must be (for all `a`, `b` and `c`):
36 /// - symmetric: `a == b` implies `b == a`; and
37 /// - transitive: `a == b` and `b == c` implies `a == c`.
39 /// Note that these requirements mean that the trait itself must be implemented
40 /// symmetrically and transitively: if `T: PartialEq<U>` and `U: PartialEq<V>`
41 /// then `U: PartialEq<T>` and `T: PartialEq<V>`.
45 /// This trait can be used with `#[derive]`. When `derive`d on structs, two
46 /// instances are equal if all fields are equal, and not equal if any fields
47 /// are not equal. When `derive`d on enums, each variant is equal to itself
48 /// and not equal to the other variants.
50 /// ## How can I implement `PartialEq`?
52 /// `PartialEq` only requires the [`eq`] method to be implemented; [`ne`] is defined
53 /// in terms of it by default. Any manual implementation of [`ne`] *must* respect
54 /// the rule that [`eq`] is a strict inverse of [`ne`]; that is, `!(a == b)` if and
57 /// Implementations of `PartialEq`, [`PartialOrd`], and [`Ord`] *must* agree with
58 /// each other. It's easy to accidentally make them disagree by deriving some
59 /// of the traits and manually implementing others.
61 /// An example implementation for a domain in which two books are considered
62 /// the same book if their ISBN matches, even if the formats differ:
73 /// format: BookFormat,
76 /// impl PartialEq for Book {
77 /// fn eq(&self, other: &Self) -> bool {
78 /// self.isbn == other.isbn
82 /// let b1 = Book { isbn: 3, format: BookFormat::Paperback };
83 /// let b2 = Book { isbn: 3, format: BookFormat::Ebook };
84 /// let b3 = Book { isbn: 10, format: BookFormat::Paperback };
86 /// assert!(b1 == b2);
87 /// assert!(b1 != b3);
90 /// ## How can I compare two different types?
92 /// The type you can compare with is controlled by `PartialEq`'s type parameter.
93 /// For example, let's tweak our previous code a bit:
96 /// // The derive implements <BookFormat> == <BookFormat> comparisons
97 /// #[derive(PartialEq)]
106 /// format: BookFormat,
109 /// // Implement <Book> == <BookFormat> comparisons
110 /// impl PartialEq<BookFormat> for Book {
111 /// fn eq(&self, other: &BookFormat) -> bool {
112 /// self.format == *other
116 /// // Implement <BookFormat> == <Book> comparisons
117 /// impl PartialEq<Book> for BookFormat {
118 /// fn eq(&self, other: &Book) -> bool {
119 /// *self == other.format
123 /// let b1 = Book { isbn: 3, format: BookFormat::Paperback };
125 /// assert!(b1 == BookFormat::Paperback);
126 /// assert!(BookFormat::Ebook != b1);
129 /// By changing `impl PartialEq for Book` to `impl PartialEq<BookFormat> for Book`,
130 /// we allow `BookFormat`s to be compared with `Book`s.
132 /// A comparison like the one above, which ignores some fields of the struct,
133 /// can be dangerous. It can easily lead to an unintended violation of the
134 /// requirements for a partial equivalence relation. For example, if we kept
135 /// the above implementation of `PartialEq<Book>` for `BookFormat` and added an
136 /// implementation of `PartialEq<Book>` for `Book` (either via a `#[derive]` or
137 /// via the manual implementation from the first example) then the result would
138 /// violate transitivity:
141 /// #[derive(PartialEq)]
142 /// enum BookFormat {
148 /// #[derive(PartialEq)]
151 /// format: BookFormat,
154 /// impl PartialEq<BookFormat> for Book {
155 /// fn eq(&self, other: &BookFormat) -> bool {
156 /// self.format == *other
160 /// impl PartialEq<Book> for BookFormat {
161 /// fn eq(&self, other: &Book) -> bool {
162 /// *self == other.format
167 /// let b1 = Book { isbn: 1, format: BookFormat::Paperback };
168 /// let b2 = Book { isbn: 2, format: BookFormat::Paperback };
170 /// assert!(b1 == BookFormat::Paperback);
171 /// assert!(BookFormat::Paperback == b2);
173 /// // The following should hold by transitivity but doesn't.
174 /// assert!(b1 == b2); // <-- PANICS
184 /// assert_eq!(x == y, false);
185 /// assert_eq!(x.eq(&y), false);
188 /// [`eq`]: PartialEq::eq
189 /// [`ne`]: PartialEq::ne
191 #[stable(feature = "rust1", since = "1.0.0")]
194 #[rustc_on_unimplemented(
195 message = "can't compare `{Self}` with `{Rhs}`",
196 label = "no implementation for `{Self} == {Rhs}`"
198 pub trait PartialEq<Rhs: ?Sized = Self> {
199 /// This method tests for `self` and `other` values to be equal, and is used
202 #[stable(feature = "rust1", since = "1.0.0")]
203 fn eq(&self, other: &Rhs) -> bool;
205 /// This method tests for `!=`.
208 #[stable(feature = "rust1", since = "1.0.0")]
209 fn ne(&self, other: &Rhs) -> bool {
214 /// Derive macro generating an impl of the trait `PartialEq`.
215 #[rustc_builtin_macro]
216 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
217 #[allow_internal_unstable(core_intrinsics, structural_match)]
218 pub macro PartialEq($item:item) {
219 /* compiler built-in */
222 /// Trait for equality comparisons which are [equivalence relations](
223 /// https://en.wikipedia.org/wiki/Equivalence_relation).
225 /// This means, that in addition to `a == b` and `a != b` being strict inverses, the equality must
226 /// be (for all `a`, `b` and `c`):
228 /// - reflexive: `a == a`;
229 /// - symmetric: `a == b` implies `b == a`; and
230 /// - transitive: `a == b` and `b == c` implies `a == c`.
232 /// This property cannot be checked by the compiler, and therefore `Eq` implies
233 /// [`PartialEq`], and has no extra methods.
237 /// This trait can be used with `#[derive]`. When `derive`d, because `Eq` has
238 /// no extra methods, it is only informing the compiler that this is an
239 /// equivalence relation rather than a partial equivalence relation. Note that
240 /// the `derive` strategy requires all fields are `Eq`, which isn't
243 /// ## How can I implement `Eq`?
245 /// If you cannot use the `derive` strategy, specify that your type implements
246 /// `Eq`, which has no methods:
249 /// enum BookFormat { Paperback, Hardback, Ebook }
252 /// format: BookFormat,
254 /// impl PartialEq for Book {
255 /// fn eq(&self, other: &Self) -> bool {
256 /// self.isbn == other.isbn
259 /// impl Eq for Book {}
263 #[stable(feature = "rust1", since = "1.0.0")]
264 pub trait Eq: PartialEq<Self> {
265 // this method is used solely by #[deriving] to assert
266 // that every component of a type implements #[deriving]
267 // itself, the current deriving infrastructure means doing this
268 // assertion without using a method on this trait is nearly
271 // This should never be implemented by hand.
274 #[stable(feature = "rust1", since = "1.0.0")]
275 fn assert_receiver_is_total_eq(&self) {}
278 /// Derive macro generating an impl of the trait `Eq`.
279 #[rustc_builtin_macro]
280 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
281 #[allow_internal_unstable(core_intrinsics, derive_eq, structural_match)]
282 pub macro Eq($item:item) {
283 /* compiler built-in */
286 // FIXME: this struct is used solely by #[derive] to
287 // assert that every component of a type implements Eq.
289 // This struct should never appear in user code.
291 #[allow(missing_debug_implementations)]
292 #[unstable(feature = "derive_eq", reason = "deriving hack, should not be public", issue = "none")]
293 pub struct AssertParamIsEq<T: Eq + ?Sized> {
294 _field: crate::marker::PhantomData<T>,
297 /// An `Ordering` is the result of a comparison between two values.
302 /// use std::cmp::Ordering;
304 /// let result = 1.cmp(&2);
305 /// assert_eq!(Ordering::Less, result);
307 /// let result = 1.cmp(&1);
308 /// assert_eq!(Ordering::Equal, result);
310 /// let result = 2.cmp(&1);
311 /// assert_eq!(Ordering::Greater, result);
313 #[derive(Clone, Copy, PartialEq, Debug, Hash)]
314 #[stable(feature = "rust1", since = "1.0.0")]
316 /// An ordering where a compared value is less than another.
317 #[stable(feature = "rust1", since = "1.0.0")]
319 /// An ordering where a compared value is equal to another.
320 #[stable(feature = "rust1", since = "1.0.0")]
322 /// An ordering where a compared value is greater than another.
323 #[stable(feature = "rust1", since = "1.0.0")]
328 /// Reverses the `Ordering`.
330 /// * `Less` becomes `Greater`.
331 /// * `Greater` becomes `Less`.
332 /// * `Equal` becomes `Equal`.
339 /// use std::cmp::Ordering;
341 /// assert_eq!(Ordering::Less.reverse(), Ordering::Greater);
342 /// assert_eq!(Ordering::Equal.reverse(), Ordering::Equal);
343 /// assert_eq!(Ordering::Greater.reverse(), Ordering::Less);
346 /// This method can be used to reverse a comparison:
349 /// let data: &mut [_] = &mut [2, 10, 5, 8];
351 /// // sort the array from largest to smallest.
352 /// data.sort_by(|a, b| a.cmp(b).reverse());
354 /// let b: &mut [_] = &mut [10, 8, 5, 2];
355 /// assert!(data == b);
359 #[rustc_const_stable(feature = "const_ordering", since = "1.48.0")]
360 #[stable(feature = "rust1", since = "1.0.0")]
361 pub const fn reverse(self) -> Ordering {
369 /// Chains two orderings.
371 /// Returns `self` when it's not `Equal`. Otherwise returns `other`.
376 /// use std::cmp::Ordering;
378 /// let result = Ordering::Equal.then(Ordering::Less);
379 /// assert_eq!(result, Ordering::Less);
381 /// let result = Ordering::Less.then(Ordering::Equal);
382 /// assert_eq!(result, Ordering::Less);
384 /// let result = Ordering::Less.then(Ordering::Greater);
385 /// assert_eq!(result, Ordering::Less);
387 /// let result = Ordering::Equal.then(Ordering::Equal);
388 /// assert_eq!(result, Ordering::Equal);
390 /// let x: (i64, i64, i64) = (1, 2, 7);
391 /// let y: (i64, i64, i64) = (1, 5, 3);
392 /// let result = x.0.cmp(&y.0).then(x.1.cmp(&y.1)).then(x.2.cmp(&y.2));
394 /// assert_eq!(result, Ordering::Less);
398 #[rustc_const_stable(feature = "const_ordering", since = "1.48.0")]
399 #[stable(feature = "ordering_chaining", since = "1.17.0")]
400 pub const fn then(self, other: Ordering) -> Ordering {
407 /// Chains the ordering with the given function.
409 /// Returns `self` when it's not `Equal`. Otherwise calls `f` and returns
415 /// use std::cmp::Ordering;
417 /// let result = Ordering::Equal.then_with(|| Ordering::Less);
418 /// assert_eq!(result, Ordering::Less);
420 /// let result = Ordering::Less.then_with(|| Ordering::Equal);
421 /// assert_eq!(result, Ordering::Less);
423 /// let result = Ordering::Less.then_with(|| Ordering::Greater);
424 /// assert_eq!(result, Ordering::Less);
426 /// let result = Ordering::Equal.then_with(|| Ordering::Equal);
427 /// assert_eq!(result, Ordering::Equal);
429 /// let x: (i64, i64, i64) = (1, 2, 7);
430 /// let y: (i64, i64, i64) = (1, 5, 3);
431 /// let result = x.0.cmp(&y.0).then_with(|| x.1.cmp(&y.1)).then_with(|| x.2.cmp(&y.2));
433 /// assert_eq!(result, Ordering::Less);
437 #[stable(feature = "ordering_chaining", since = "1.17.0")]
438 pub fn then_with<F: FnOnce() -> Ordering>(self, f: F) -> Ordering {
446 /// A helper struct for reverse ordering.
448 /// This struct is a helper to be used with functions like [`Vec::sort_by_key`] and
449 /// can be used to reverse order a part of a key.
451 /// [`Vec::sort_by_key`]: ../../std/vec/struct.Vec.html#method.sort_by_key
456 /// use std::cmp::Reverse;
458 /// let mut v = vec![1, 2, 3, 4, 5, 6];
459 /// v.sort_by_key(|&num| (num > 3, Reverse(num)));
460 /// assert_eq!(v, vec![3, 2, 1, 6, 5, 4]);
462 #[derive(PartialEq, Eq, Debug, Copy, Clone, Default, Hash)]
463 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
464 pub struct Reverse<T>(#[stable(feature = "reverse_cmp_key", since = "1.19.0")] pub T);
466 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
467 impl<T: PartialOrd> PartialOrd for Reverse<T> {
469 fn partial_cmp(&self, other: &Reverse<T>) -> Option<Ordering> {
470 other.0.partial_cmp(&self.0)
474 fn lt(&self, other: &Self) -> bool {
478 fn le(&self, other: &Self) -> bool {
482 fn gt(&self, other: &Self) -> bool {
486 fn ge(&self, other: &Self) -> bool {
491 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
492 impl<T: Ord> Ord for Reverse<T> {
494 fn cmp(&self, other: &Reverse<T>) -> Ordering {
499 /// Trait for types that form a [total order](https://en.wikipedia.org/wiki/Total_order).
501 /// An order is a total order if it is (for all `a`, `b` and `c`):
503 /// - total and asymmetric: exactly one of `a < b`, `a == b` or `a > b` is true; and
504 /// - transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
508 /// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a
509 /// [lexicographic](https://en.wikipedia.org/wiki/Lexicographic_order) ordering based on the top-to-bottom declaration order of the struct's members.
510 /// When `derive`d on enums, variants are ordered by their top-to-bottom discriminant order.
512 /// ## Lexicographical comparison
514 /// Lexicographical comparison is an operation with the following properties:
515 /// - Two sequences are compared element by element.
516 /// - The first mismatching element defines which sequence is lexicographically less or greater than the other.
517 /// - If one sequence is a prefix of another, the shorter sequence is lexicographically less than the other.
518 /// - If two sequence have equivalent elements and are of the same length, then the sequences are lexicographically equal.
519 /// - An empty sequence is lexicographically less than any non-empty sequence.
520 /// - Two empty sequences are lexicographically equal.
522 /// ## How can I implement `Ord`?
524 /// `Ord` requires that the type also be [`PartialOrd`] and [`Eq`] (which requires [`PartialEq`]).
526 /// Then you must define an implementation for [`cmp`]. You may find it useful to use
527 /// [`cmp`] on your type's fields.
529 /// Implementations of [`PartialEq`], [`PartialOrd`], and `Ord` *must*
530 /// agree with each other. That is, `a.cmp(b) == Ordering::Equal` if
531 /// and only if `a == b` and `Some(a.cmp(b)) == a.partial_cmp(b)` for
532 /// all `a` and `b`. It's easy to accidentally make them disagree by
533 /// deriving some of the traits and manually implementing others.
535 /// Here's an example where you want to sort people by height only, disregarding `id`
539 /// use std::cmp::Ordering;
548 /// impl Ord for Person {
549 /// fn cmp(&self, other: &Self) -> Ordering {
550 /// self.height.cmp(&other.height)
554 /// impl PartialOrd for Person {
555 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
556 /// Some(self.cmp(other))
560 /// impl PartialEq for Person {
561 /// fn eq(&self, other: &Self) -> bool {
562 /// self.height == other.height
567 /// [`cmp`]: Ord::cmp
572 #[stable(feature = "rust1", since = "1.0.0")]
573 pub trait Ord: Eq + PartialOrd<Self> {
574 /// This method returns an [`Ordering`] between `self` and `other`.
576 /// By convention, `self.cmp(&other)` returns the ordering matching the expression
577 /// `self <operator> other` if true.
582 /// use std::cmp::Ordering;
584 /// assert_eq!(5.cmp(&10), Ordering::Less);
585 /// assert_eq!(10.cmp(&5), Ordering::Greater);
586 /// assert_eq!(5.cmp(&5), Ordering::Equal);
589 #[stable(feature = "rust1", since = "1.0.0")]
590 fn cmp(&self, other: &Self) -> Ordering;
592 /// Compares and returns the maximum of two values.
594 /// Returns the second argument if the comparison determines them to be equal.
599 /// assert_eq!(2, 1.max(2));
600 /// assert_eq!(2, 2.max(2));
602 #[stable(feature = "ord_max_min", since = "1.21.0")]
605 fn max(self, other: Self) -> Self
609 max_by(self, other, Ord::cmp)
612 /// Compares and returns the minimum of two values.
614 /// Returns the first argument if the comparison determines them to be equal.
619 /// assert_eq!(1, 1.min(2));
620 /// assert_eq!(2, 2.min(2));
622 #[stable(feature = "ord_max_min", since = "1.21.0")]
625 fn min(self, other: Self) -> Self
629 min_by(self, other, Ord::cmp)
632 /// Restrict a value to a certain interval.
634 /// Returns `max` if `self` is greater than `max`, and `min` if `self` is
635 /// less than `min`. Otherwise this returns `self`.
639 /// Panics if `min > max`.
644 /// assert!((-3).clamp(-2, 1) == -2);
645 /// assert!(0.clamp(-2, 1) == 0);
646 /// assert!(2.clamp(-2, 1) == 1);
649 #[stable(feature = "clamp", since = "1.50.0")]
650 fn clamp(self, min: Self, max: Self) -> Self
657 } else if self > max {
665 /// Derive macro generating an impl of the trait `Ord`.
666 #[rustc_builtin_macro]
667 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
668 #[allow_internal_unstable(core_intrinsics)]
669 pub macro Ord($item:item) {
670 /* compiler built-in */
673 #[stable(feature = "rust1", since = "1.0.0")]
674 impl Eq for Ordering {}
676 #[stable(feature = "rust1", since = "1.0.0")]
677 impl Ord for Ordering {
679 fn cmp(&self, other: &Ordering) -> Ordering {
680 (*self as i32).cmp(&(*other as i32))
684 #[stable(feature = "rust1", since = "1.0.0")]
685 impl PartialOrd for Ordering {
687 fn partial_cmp(&self, other: &Ordering) -> Option<Ordering> {
688 (*self as i32).partial_cmp(&(*other as i32))
692 /// Trait for values that can be compared for a sort-order.
694 /// The comparison must satisfy, for all `a`, `b` and `c`:
696 /// - asymmetry: if `a < b` then `!(a > b)`, as well as `a > b` implying `!(a < b)`; and
697 /// - transitivity: `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
699 /// Note that these requirements mean that the trait itself must be implemented symmetrically and
700 /// transitively: if `T: PartialOrd<U>` and `U: PartialOrd<V>` then `U: PartialOrd<T>` and `T:
705 /// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a
706 /// lexicographic ordering based on the top-to-bottom declaration order of the struct's members.
707 /// When `derive`d on enums, variants are ordered by their top-to-bottom discriminant order.
709 /// ## How can I implement `PartialOrd`?
711 /// `PartialOrd` only requires implementation of the [`partial_cmp`] method, with the others
712 /// generated from default implementations.
714 /// However it remains possible to implement the others separately for types which do not have a
715 /// total order. For example, for floating point numbers, `NaN < 0 == false` and `NaN >= 0 ==
716 /// false` (cf. IEEE 754-2008 section 5.11).
718 /// `PartialOrd` requires your type to be [`PartialEq`].
720 /// Implementations of [`PartialEq`], `PartialOrd`, and [`Ord`] *must* agree with each other. It's
721 /// easy to accidentally make them disagree by deriving some of the traits and manually
722 /// implementing others.
724 /// If your type is [`Ord`], you can implement [`partial_cmp`] by using [`cmp`]:
727 /// use std::cmp::Ordering;
736 /// impl PartialOrd for Person {
737 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
738 /// Some(self.cmp(other))
742 /// impl Ord for Person {
743 /// fn cmp(&self, other: &Self) -> Ordering {
744 /// self.height.cmp(&other.height)
748 /// impl PartialEq for Person {
749 /// fn eq(&self, other: &Self) -> bool {
750 /// self.height == other.height
755 /// You may also find it useful to use [`partial_cmp`] on your type's fields. Here
756 /// is an example of `Person` types who have a floating-point `height` field that
757 /// is the only field to be used for sorting:
760 /// use std::cmp::Ordering;
768 /// impl PartialOrd for Person {
769 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
770 /// self.height.partial_cmp(&other.height)
774 /// impl PartialEq for Person {
775 /// fn eq(&self, other: &Self) -> bool {
776 /// self.height == other.height
787 /// assert_eq!(x < y, true);
788 /// assert_eq!(x.lt(&y), true);
791 /// [`partial_cmp`]: PartialOrd::partial_cmp
792 /// [`cmp`]: Ord::cmp
793 #[lang = "partial_ord"]
794 #[stable(feature = "rust1", since = "1.0.0")]
799 #[rustc_on_unimplemented(
800 message = "can't compare `{Self}` with `{Rhs}`",
801 label = "no implementation for `{Self} < {Rhs}` and `{Self} > {Rhs}`"
803 pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
804 /// This method returns an ordering between `self` and `other` values if one exists.
809 /// use std::cmp::Ordering;
811 /// let result = 1.0.partial_cmp(&2.0);
812 /// assert_eq!(result, Some(Ordering::Less));
814 /// let result = 1.0.partial_cmp(&1.0);
815 /// assert_eq!(result, Some(Ordering::Equal));
817 /// let result = 2.0.partial_cmp(&1.0);
818 /// assert_eq!(result, Some(Ordering::Greater));
821 /// When comparison is impossible:
824 /// let result = f64::NAN.partial_cmp(&1.0);
825 /// assert_eq!(result, None);
828 #[stable(feature = "rust1", since = "1.0.0")]
829 fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>;
831 /// This method tests less than (for `self` and `other`) and is used by the `<` operator.
836 /// let result = 1.0 < 2.0;
837 /// assert_eq!(result, true);
839 /// let result = 2.0 < 1.0;
840 /// assert_eq!(result, false);
844 #[stable(feature = "rust1", since = "1.0.0")]
845 fn lt(&self, other: &Rhs) -> bool {
846 matches!(self.partial_cmp(other), Some(Less))
849 /// This method tests less than or equal to (for `self` and `other`) and is used by the `<=`
855 /// let result = 1.0 <= 2.0;
856 /// assert_eq!(result, true);
858 /// let result = 2.0 <= 2.0;
859 /// assert_eq!(result, true);
863 #[stable(feature = "rust1", since = "1.0.0")]
864 fn le(&self, other: &Rhs) -> bool {
865 matches!(self.partial_cmp(other), Some(Less | Equal))
868 /// This method tests greater than (for `self` and `other`) and is used by the `>` operator.
873 /// let result = 1.0 > 2.0;
874 /// assert_eq!(result, false);
876 /// let result = 2.0 > 2.0;
877 /// assert_eq!(result, false);
881 #[stable(feature = "rust1", since = "1.0.0")]
882 fn gt(&self, other: &Rhs) -> bool {
883 matches!(self.partial_cmp(other), Some(Greater))
886 /// This method tests greater than or equal to (for `self` and `other`) and is used by the `>=`
892 /// let result = 2.0 >= 1.0;
893 /// assert_eq!(result, true);
895 /// let result = 2.0 >= 2.0;
896 /// assert_eq!(result, true);
900 #[stable(feature = "rust1", since = "1.0.0")]
901 fn ge(&self, other: &Rhs) -> bool {
902 matches!(self.partial_cmp(other), Some(Greater | Equal))
906 /// Derive macro generating an impl of the trait `PartialOrd`.
907 #[rustc_builtin_macro]
908 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
909 #[allow_internal_unstable(core_intrinsics)]
910 pub macro PartialOrd($item:item) {
911 /* compiler built-in */
914 /// Compares and returns the minimum of two values.
916 /// Returns the first argument if the comparison determines them to be equal.
918 /// Internally uses an alias to [`Ord::min`].
925 /// assert_eq!(1, cmp::min(1, 2));
926 /// assert_eq!(2, cmp::min(2, 2));
930 #[stable(feature = "rust1", since = "1.0.0")]
931 pub fn min<T: Ord>(v1: T, v2: T) -> T {
935 /// Returns the minimum of two values with respect to the specified comparison function.
937 /// Returns the first argument if the comparison determines them to be equal.
942 /// #![feature(cmp_min_max_by)]
946 /// assert_eq!(cmp::min_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), 1);
947 /// assert_eq!(cmp::min_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), -2);
951 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
952 pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
953 match compare(&v1, &v2) {
954 Ordering::Less | Ordering::Equal => v1,
955 Ordering::Greater => v2,
959 /// Returns the element that gives the minimum value from the specified function.
961 /// Returns the first argument if the comparison determines them to be equal.
966 /// #![feature(cmp_min_max_by)]
970 /// assert_eq!(cmp::min_by_key(-2, 1, |x: &i32| x.abs()), 1);
971 /// assert_eq!(cmp::min_by_key(-2, 2, |x: &i32| x.abs()), -2);
975 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
976 pub fn min_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
977 min_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
980 /// Compares and returns the maximum of two values.
982 /// Returns the second argument if the comparison determines them to be equal.
984 /// Internally uses an alias to [`Ord::max`].
991 /// assert_eq!(2, cmp::max(1, 2));
992 /// assert_eq!(2, cmp::max(2, 2));
996 #[stable(feature = "rust1", since = "1.0.0")]
997 pub fn max<T: Ord>(v1: T, v2: T) -> T {
1001 /// Returns the maximum of two values with respect to the specified comparison function.
1003 /// Returns the second argument if the comparison determines them to be equal.
1008 /// #![feature(cmp_min_max_by)]
1012 /// assert_eq!(cmp::max_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), -2);
1013 /// assert_eq!(cmp::max_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), 2);
1017 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
1018 pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
1019 match compare(&v1, &v2) {
1020 Ordering::Less | Ordering::Equal => v2,
1021 Ordering::Greater => v1,
1025 /// Returns the element that gives the maximum value from the specified function.
1027 /// Returns the second argument if the comparison determines them to be equal.
1032 /// #![feature(cmp_min_max_by)]
1036 /// assert_eq!(cmp::max_by_key(-2, 1, |x: &i32| x.abs()), -2);
1037 /// assert_eq!(cmp::max_by_key(-2, 2, |x: &i32| x.abs()), 2);
1041 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
1042 pub fn max_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
1043 max_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
1046 // Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types
1048 use crate::cmp::Ordering::{self, Equal, Greater, Less};
1049 use crate::hint::unreachable_unchecked;
1051 macro_rules! partial_eq_impl {
1053 #[stable(feature = "rust1", since = "1.0.0")]
1054 impl PartialEq for $t {
1056 fn eq(&self, other: &$t) -> bool { (*self) == (*other) }
1058 fn ne(&self, other: &$t) -> bool { (*self) != (*other) }
1063 #[stable(feature = "rust1", since = "1.0.0")]
1064 impl PartialEq for () {
1066 fn eq(&self, _other: &()) -> bool {
1070 fn ne(&self, _other: &()) -> bool {
1076 bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64
1079 macro_rules! eq_impl {
1081 #[stable(feature = "rust1", since = "1.0.0")]
1086 eq_impl! { () bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
1088 macro_rules! partial_ord_impl {
1090 #[stable(feature = "rust1", since = "1.0.0")]
1091 impl PartialOrd for $t {
1093 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
1094 match (self <= other, self >= other) {
1095 (false, false) => None,
1096 (false, true) => Some(Greater),
1097 (true, false) => Some(Less),
1098 (true, true) => Some(Equal),
1102 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
1104 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
1106 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
1108 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
1113 #[stable(feature = "rust1", since = "1.0.0")]
1114 impl PartialOrd for () {
1116 fn partial_cmp(&self, _: &()) -> Option<Ordering> {
1121 #[stable(feature = "rust1", since = "1.0.0")]
1122 impl PartialOrd for bool {
1124 fn partial_cmp(&self, other: &bool) -> Option<Ordering> {
1125 (*self as u8).partial_cmp(&(*other as u8))
1129 partial_ord_impl! { f32 f64 }
1131 macro_rules! ord_impl {
1133 #[stable(feature = "rust1", since = "1.0.0")]
1134 impl PartialOrd for $t {
1136 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
1137 Some(self.cmp(other))
1140 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
1142 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
1144 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
1146 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
1149 #[stable(feature = "rust1", since = "1.0.0")]
1152 fn cmp(&self, other: &$t) -> Ordering {
1153 // The order here is important to generate more optimal assembly.
1154 // See <https://github.com/rust-lang/rust/issues/63758> for more info.
1155 if *self < *other { Less }
1156 else if *self == *other { Equal }
1163 #[stable(feature = "rust1", since = "1.0.0")]
1166 fn cmp(&self, _other: &()) -> Ordering {
1171 #[stable(feature = "rust1", since = "1.0.0")]
1174 fn cmp(&self, other: &bool) -> Ordering {
1175 // Casting to i8's and converting the difference to an Ordering generates
1176 // more optimal assembly.
1177 // See <https://github.com/rust-lang/rust/issues/66780> for more info.
1178 match (*self as i8) - (*other as i8) {
1182 // SAFETY: bool as i8 returns 0 or 1, so the difference can't be anything else
1183 _ => unsafe { unreachable_unchecked() },
1188 ord_impl! { char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
1190 #[unstable(feature = "never_type", issue = "35121")]
1191 impl PartialEq for ! {
1192 fn eq(&self, _: &!) -> bool {
1197 #[unstable(feature = "never_type", issue = "35121")]
1200 #[unstable(feature = "never_type", issue = "35121")]
1201 impl PartialOrd for ! {
1202 fn partial_cmp(&self, _: &!) -> Option<Ordering> {
1207 #[unstable(feature = "never_type", issue = "35121")]
1209 fn cmp(&self, _: &!) -> Ordering {
1216 #[stable(feature = "rust1", since = "1.0.0")]
1217 impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &A
1222 fn eq(&self, other: &&B) -> bool {
1223 PartialEq::eq(*self, *other)
1226 fn ne(&self, other: &&B) -> bool {
1227 PartialEq::ne(*self, *other)
1230 #[stable(feature = "rust1", since = "1.0.0")]
1231 impl<A: ?Sized, B: ?Sized> PartialOrd<&B> for &A
1236 fn partial_cmp(&self, other: &&B) -> Option<Ordering> {
1237 PartialOrd::partial_cmp(*self, *other)
1240 fn lt(&self, other: &&B) -> bool {
1241 PartialOrd::lt(*self, *other)
1244 fn le(&self, other: &&B) -> bool {
1245 PartialOrd::le(*self, *other)
1248 fn gt(&self, other: &&B) -> bool {
1249 PartialOrd::gt(*self, *other)
1252 fn ge(&self, other: &&B) -> bool {
1253 PartialOrd::ge(*self, *other)
1256 #[stable(feature = "rust1", since = "1.0.0")]
1257 impl<A: ?Sized> Ord for &A
1262 fn cmp(&self, other: &Self) -> Ordering {
1263 Ord::cmp(*self, *other)
1266 #[stable(feature = "rust1", since = "1.0.0")]
1267 impl<A: ?Sized> Eq for &A where A: Eq {}
1271 #[stable(feature = "rust1", since = "1.0.0")]
1272 impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &mut A
1277 fn eq(&self, other: &&mut B) -> bool {
1278 PartialEq::eq(*self, *other)
1281 fn ne(&self, other: &&mut B) -> bool {
1282 PartialEq::ne(*self, *other)
1285 #[stable(feature = "rust1", since = "1.0.0")]
1286 impl<A: ?Sized, B: ?Sized> PartialOrd<&mut B> for &mut A
1291 fn partial_cmp(&self, other: &&mut B) -> Option<Ordering> {
1292 PartialOrd::partial_cmp(*self, *other)
1295 fn lt(&self, other: &&mut B) -> bool {
1296 PartialOrd::lt(*self, *other)
1299 fn le(&self, other: &&mut B) -> bool {
1300 PartialOrd::le(*self, *other)
1303 fn gt(&self, other: &&mut B) -> bool {
1304 PartialOrd::gt(*self, *other)
1307 fn ge(&self, other: &&mut B) -> bool {
1308 PartialOrd::ge(*self, *other)
1311 #[stable(feature = "rust1", since = "1.0.0")]
1312 impl<A: ?Sized> Ord for &mut A
1317 fn cmp(&self, other: &Self) -> Ordering {
1318 Ord::cmp(*self, *other)
1321 #[stable(feature = "rust1", since = "1.0.0")]
1322 impl<A: ?Sized> Eq for &mut A where A: Eq {}
1324 #[stable(feature = "rust1", since = "1.0.0")]
1325 impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &A
1330 fn eq(&self, other: &&mut B) -> bool {
1331 PartialEq::eq(*self, *other)
1334 fn ne(&self, other: &&mut B) -> bool {
1335 PartialEq::ne(*self, *other)
1339 #[stable(feature = "rust1", since = "1.0.0")]
1340 impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &mut A
1345 fn eq(&self, other: &&B) -> bool {
1346 PartialEq::eq(*self, *other)
1349 fn ne(&self, other: &&B) -> bool {
1350 PartialEq::ne(*self, *other)