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`](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 #[stable(feature = "rust1", since = "1.0.0")]
360 pub fn reverse(self) -> Ordering {
368 /// Chains two orderings.
370 /// Returns `self` when it's not `Equal`. Otherwise returns `other`.
375 /// use std::cmp::Ordering;
377 /// let result = Ordering::Equal.then(Ordering::Less);
378 /// assert_eq!(result, Ordering::Less);
380 /// let result = Ordering::Less.then(Ordering::Equal);
381 /// assert_eq!(result, Ordering::Less);
383 /// let result = Ordering::Less.then(Ordering::Greater);
384 /// assert_eq!(result, Ordering::Less);
386 /// let result = Ordering::Equal.then(Ordering::Equal);
387 /// assert_eq!(result, Ordering::Equal);
389 /// let x: (i64, i64, i64) = (1, 2, 7);
390 /// let y: (i64, i64, i64) = (1, 5, 3);
391 /// let result = x.0.cmp(&y.0).then(x.1.cmp(&y.1)).then(x.2.cmp(&y.2));
393 /// assert_eq!(result, Ordering::Less);
397 #[stable(feature = "ordering_chaining", since = "1.17.0")]
398 pub fn then(self, other: Ordering) -> Ordering {
405 /// Chains the ordering with the given function.
407 /// Returns `self` when it's not `Equal`. Otherwise calls `f` and returns
413 /// use std::cmp::Ordering;
415 /// let result = Ordering::Equal.then_with(|| Ordering::Less);
416 /// assert_eq!(result, Ordering::Less);
418 /// let result = Ordering::Less.then_with(|| Ordering::Equal);
419 /// assert_eq!(result, Ordering::Less);
421 /// let result = Ordering::Less.then_with(|| Ordering::Greater);
422 /// assert_eq!(result, Ordering::Less);
424 /// let result = Ordering::Equal.then_with(|| Ordering::Equal);
425 /// assert_eq!(result, Ordering::Equal);
427 /// let x: (i64, i64, i64) = (1, 2, 7);
428 /// let y: (i64, i64, i64) = (1, 5, 3);
429 /// let result = x.0.cmp(&y.0).then_with(|| x.1.cmp(&y.1)).then_with(|| x.2.cmp(&y.2));
431 /// assert_eq!(result, Ordering::Less);
435 #[stable(feature = "ordering_chaining", since = "1.17.0")]
436 pub fn then_with<F: FnOnce() -> Ordering>(self, f: F) -> Ordering {
444 /// A helper struct for reverse ordering.
446 /// This struct is a helper to be used with functions like [`Vec::sort_by_key`] and
447 /// can be used to reverse order a part of a key.
449 /// [`Vec::sort_by_key`]: ../../std/vec/struct.Vec.html#method.sort_by_key
454 /// use std::cmp::Reverse;
456 /// let mut v = vec![1, 2, 3, 4, 5, 6];
457 /// v.sort_by_key(|&num| (num > 3, Reverse(num)));
458 /// assert_eq!(v, vec![3, 2, 1, 6, 5, 4]);
460 #[derive(PartialEq, Eq, Debug, Copy, Clone, Default, Hash)]
461 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
462 pub struct Reverse<T>(#[stable(feature = "reverse_cmp_key", since = "1.19.0")] pub T);
464 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
465 impl<T: PartialOrd> PartialOrd for Reverse<T> {
467 fn partial_cmp(&self, other: &Reverse<T>) -> Option<Ordering> {
468 other.0.partial_cmp(&self.0)
472 fn lt(&self, other: &Self) -> bool {
476 fn le(&self, other: &Self) -> bool {
480 fn gt(&self, other: &Self) -> bool {
484 fn ge(&self, other: &Self) -> bool {
489 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
490 impl<T: Ord> Ord for Reverse<T> {
492 fn cmp(&self, other: &Reverse<T>) -> Ordering {
497 /// Trait for types that form a [total order](https://en.wikipedia.org/wiki/Total_order).
499 /// An order is a total order if it is (for all `a`, `b` and `c`):
501 /// - total and asymmetric: exactly one of `a < b`, `a == b` or `a > b` is true; and
502 /// - transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
506 /// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a
507 /// lexicographic ordering based on the top-to-bottom declaration order of the struct's members.
508 /// When `derive`d on enums, variants are ordered by their top-to-bottom discriminant order.
510 /// ## How can I implement `Ord`?
512 /// `Ord` requires that the type also be [`PartialOrd`] and [`Eq`] (which requires [`PartialEq`]).
514 /// Then you must define an implementation for [`cmp`]. You may find it useful to use
515 /// [`cmp`] on your type's fields.
517 /// Implementations of [`PartialEq`], [`PartialOrd`], and `Ord` *must*
518 /// agree with each other. That is, `a.cmp(b) == Ordering::Equal` if
519 /// and only if `a == b` and `Some(a.cmp(b)) == a.partial_cmp(b)` for
520 /// all `a` and `b`. It's easy to accidentally make them disagree by
521 /// deriving some of the traits and manually implementing others.
523 /// Here's an example where you want to sort people by height only, disregarding `id`
527 /// use std::cmp::Ordering;
536 /// impl Ord for Person {
537 /// fn cmp(&self, other: &Self) -> Ordering {
538 /// self.height.cmp(&other.height)
542 /// impl PartialOrd for Person {
543 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
544 /// Some(self.cmp(other))
548 /// impl PartialEq for Person {
549 /// fn eq(&self, other: &Self) -> bool {
550 /// self.height == other.height
555 /// [`cmp`]: Ord::cmp
560 #[stable(feature = "rust1", since = "1.0.0")]
561 pub trait Ord: Eq + PartialOrd<Self> {
562 /// This method returns an [`Ordering`] between `self` and `other`.
564 /// By convention, `self.cmp(&other)` returns the ordering matching the expression
565 /// `self <operator> other` if true.
570 /// use std::cmp::Ordering;
572 /// assert_eq!(5.cmp(&10), Ordering::Less);
573 /// assert_eq!(10.cmp(&5), Ordering::Greater);
574 /// assert_eq!(5.cmp(&5), Ordering::Equal);
577 #[stable(feature = "rust1", since = "1.0.0")]
578 fn cmp(&self, other: &Self) -> Ordering;
580 /// Compares and returns the maximum of two values.
582 /// Returns the second argument if the comparison determines them to be equal.
587 /// assert_eq!(2, 1.max(2));
588 /// assert_eq!(2, 2.max(2));
590 #[stable(feature = "ord_max_min", since = "1.21.0")]
593 fn max(self, other: Self) -> Self
597 max_by(self, other, Ord::cmp)
600 /// Compares and returns the minimum of two values.
602 /// Returns the first argument if the comparison determines them to be equal.
607 /// assert_eq!(1, 1.min(2));
608 /// assert_eq!(2, 2.min(2));
610 #[stable(feature = "ord_max_min", since = "1.21.0")]
613 fn min(self, other: Self) -> Self
617 min_by(self, other, Ord::cmp)
620 /// Restrict a value to a certain interval.
622 /// Returns `max` if `self` is greater than `max`, and `min` if `self` is
623 /// less than `min`. Otherwise this returns `self`.
627 /// Panics if `min > max`.
632 /// #![feature(clamp)]
634 /// assert!((-3).clamp(-2, 1) == -2);
635 /// assert!(0.clamp(-2, 1) == 0);
636 /// assert!(2.clamp(-2, 1) == 1);
639 #[unstable(feature = "clamp", issue = "44095")]
640 fn clamp(self, min: Self, max: Self) -> Self
647 } else if self > max {
655 /// Derive macro generating an impl of the trait `Ord`.
656 #[rustc_builtin_macro]
657 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
658 #[allow_internal_unstable(core_intrinsics)]
659 pub macro Ord($item:item) {
660 /* compiler built-in */
663 #[stable(feature = "rust1", since = "1.0.0")]
664 impl Eq for Ordering {}
666 #[stable(feature = "rust1", since = "1.0.0")]
667 impl Ord for Ordering {
669 fn cmp(&self, other: &Ordering) -> Ordering {
670 (*self as i32).cmp(&(*other as i32))
674 #[stable(feature = "rust1", since = "1.0.0")]
675 impl PartialOrd for Ordering {
677 fn partial_cmp(&self, other: &Ordering) -> Option<Ordering> {
678 (*self as i32).partial_cmp(&(*other as i32))
682 /// Trait for values that can be compared for a sort-order.
684 /// The comparison must satisfy, for all `a`, `b` and `c`:
686 /// - asymmetry: if `a < b` then `!(a > b)`, as well as `a > b` implying `!(a < b)`; and
687 /// - transitivity: `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
689 /// Note that these requirements mean that the trait itself must be implemented symmetrically and
690 /// transitively: if `T: PartialOrd<U>` and `U: PartialOrd<V>` then `U: PartialOrd<T>` and `T:
695 /// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a
696 /// lexicographic ordering based on the top-to-bottom declaration order of the struct's members.
697 /// When `derive`d on enums, variants are ordered by their top-to-bottom discriminant order.
699 /// ## How can I implement `PartialOrd`?
701 /// `PartialOrd` only requires implementation of the [`partial_cmp`] method, with the others
702 /// generated from default implementations.
704 /// However it remains possible to implement the others separately for types which do not have a
705 /// total order. For example, for floating point numbers, `NaN < 0 == false` and `NaN >= 0 ==
706 /// false` (cf. IEEE 754-2008 section 5.11).
708 /// `PartialOrd` requires your type to be [`PartialEq`].
710 /// Implementations of [`PartialEq`], `PartialOrd`, and [`Ord`] *must* agree with each other. It's
711 /// easy to accidentally make them disagree by deriving some of the traits and manually
712 /// implementing others.
714 /// If your type is [`Ord`], you can implement [`partial_cmp`] by using [`cmp`]:
717 /// use std::cmp::Ordering;
726 /// impl PartialOrd for Person {
727 /// fn partial_cmp(&self, other: &Person) -> Option<Ordering> {
728 /// Some(self.cmp(other))
732 /// impl Ord for Person {
733 /// fn cmp(&self, other: &Person) -> Ordering {
734 /// self.height.cmp(&other.height)
738 /// impl PartialEq for Person {
739 /// fn eq(&self, other: &Person) -> bool {
740 /// self.height == other.height
745 /// You may also find it useful to use [`partial_cmp`] on your type's fields. Here
746 /// is an example of `Person` types who have a floating-point `height` field that
747 /// is the only field to be used for sorting:
750 /// use std::cmp::Ordering;
758 /// impl PartialOrd for Person {
759 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
760 /// self.height.partial_cmp(&other.height)
764 /// impl PartialEq for Person {
765 /// fn eq(&self, other: &Self) -> bool {
766 /// self.height == other.height
777 /// assert_eq!(x < y, true);
778 /// assert_eq!(x.lt(&y), true);
781 /// [`partial_cmp`]: PartialOrd::partial_cmp
782 /// [`cmp`]: Ord::cmp
783 #[lang = "partial_ord"]
784 #[stable(feature = "rust1", since = "1.0.0")]
789 #[rustc_on_unimplemented(
790 message = "can't compare `{Self}` with `{Rhs}`",
791 label = "no implementation for `{Self} < {Rhs}` and `{Self} > {Rhs}`"
793 pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
794 /// This method returns an ordering between `self` and `other` values if one exists.
799 /// use std::cmp::Ordering;
801 /// let result = 1.0.partial_cmp(&2.0);
802 /// assert_eq!(result, Some(Ordering::Less));
804 /// let result = 1.0.partial_cmp(&1.0);
805 /// assert_eq!(result, Some(Ordering::Equal));
807 /// let result = 2.0.partial_cmp(&1.0);
808 /// assert_eq!(result, Some(Ordering::Greater));
811 /// When comparison is impossible:
814 /// let result = f64::NAN.partial_cmp(&1.0);
815 /// assert_eq!(result, None);
818 #[stable(feature = "rust1", since = "1.0.0")]
819 fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>;
821 /// This method tests less than (for `self` and `other`) and is used by the `<` operator.
826 /// let result = 1.0 < 2.0;
827 /// assert_eq!(result, true);
829 /// let result = 2.0 < 1.0;
830 /// assert_eq!(result, false);
834 #[stable(feature = "rust1", since = "1.0.0")]
835 fn lt(&self, other: &Rhs) -> bool {
836 matches!(self.partial_cmp(other), Some(Less))
839 /// This method tests less than or equal to (for `self` and `other`) and is used by the `<=`
845 /// let result = 1.0 <= 2.0;
846 /// assert_eq!(result, true);
848 /// let result = 2.0 <= 2.0;
849 /// assert_eq!(result, true);
853 #[stable(feature = "rust1", since = "1.0.0")]
854 fn le(&self, other: &Rhs) -> bool {
855 matches!(self.partial_cmp(other), Some(Less | Equal))
858 /// This method tests greater than (for `self` and `other`) and is used by the `>` operator.
863 /// let result = 1.0 > 2.0;
864 /// assert_eq!(result, false);
866 /// let result = 2.0 > 2.0;
867 /// assert_eq!(result, false);
871 #[stable(feature = "rust1", since = "1.0.0")]
872 fn gt(&self, other: &Rhs) -> bool {
873 matches!(self.partial_cmp(other), Some(Greater))
876 /// This method tests greater than or equal to (for `self` and `other`) and is used by the `>=`
882 /// let result = 2.0 >= 1.0;
883 /// assert_eq!(result, true);
885 /// let result = 2.0 >= 2.0;
886 /// assert_eq!(result, true);
890 #[stable(feature = "rust1", since = "1.0.0")]
891 fn ge(&self, other: &Rhs) -> bool {
892 matches!(self.partial_cmp(other), Some(Greater | Equal))
896 /// Derive macro generating an impl of the trait `PartialOrd`.
897 #[rustc_builtin_macro]
898 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
899 #[allow_internal_unstable(core_intrinsics)]
900 pub macro PartialOrd($item:item) {
901 /* compiler built-in */
904 /// Compares and returns the minimum of two values.
906 /// Returns the first argument if the comparison determines them to be equal.
908 /// Internally uses an alias to [`Ord::min`].
915 /// assert_eq!(1, cmp::min(1, 2));
916 /// assert_eq!(2, cmp::min(2, 2));
920 #[stable(feature = "rust1", since = "1.0.0")]
921 pub fn min<T: Ord>(v1: T, v2: T) -> T {
925 /// Returns the minimum of two values with respect to the specified comparison function.
927 /// Returns the first argument if the comparison determines them to be equal.
932 /// #![feature(cmp_min_max_by)]
936 /// assert_eq!(cmp::min_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), 1);
937 /// assert_eq!(cmp::min_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), -2);
941 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
942 pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
943 match compare(&v1, &v2) {
944 Ordering::Less | Ordering::Equal => v1,
945 Ordering::Greater => v2,
949 /// Returns the element that gives the minimum value from the specified function.
951 /// Returns the first argument if the comparison determines them to be equal.
956 /// #![feature(cmp_min_max_by)]
960 /// assert_eq!(cmp::min_by_key(-2, 1, |x: &i32| x.abs()), 1);
961 /// assert_eq!(cmp::min_by_key(-2, 2, |x: &i32| x.abs()), -2);
965 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
966 pub fn min_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
967 min_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
970 /// Compares and returns the maximum of two values.
972 /// Returns the second argument if the comparison determines them to be equal.
974 /// Internally uses an alias to [`Ord::max`].
981 /// assert_eq!(2, cmp::max(1, 2));
982 /// assert_eq!(2, cmp::max(2, 2));
986 #[stable(feature = "rust1", since = "1.0.0")]
987 pub fn max<T: Ord>(v1: T, v2: T) -> T {
991 /// Returns the maximum of two values with respect to the specified comparison function.
993 /// Returns the second argument if the comparison determines them to be equal.
998 /// #![feature(cmp_min_max_by)]
1002 /// assert_eq!(cmp::max_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), -2);
1003 /// assert_eq!(cmp::max_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), 2);
1007 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
1008 pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
1009 match compare(&v1, &v2) {
1010 Ordering::Less | Ordering::Equal => v2,
1011 Ordering::Greater => v1,
1015 /// Returns the element that gives the maximum value from the specified function.
1017 /// Returns the second argument if the comparison determines them to be equal.
1022 /// #![feature(cmp_min_max_by)]
1026 /// assert_eq!(cmp::max_by_key(-2, 1, |x: &i32| x.abs()), -2);
1027 /// assert_eq!(cmp::max_by_key(-2, 2, |x: &i32| x.abs()), 2);
1031 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
1032 pub fn max_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
1033 max_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
1036 // Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types
1038 use crate::cmp::Ordering::{self, Equal, Greater, Less};
1039 use crate::hint::unreachable_unchecked;
1041 macro_rules! partial_eq_impl {
1043 #[stable(feature = "rust1", since = "1.0.0")]
1044 impl PartialEq for $t {
1046 fn eq(&self, other: &$t) -> bool { (*self) == (*other) }
1048 fn ne(&self, other: &$t) -> bool { (*self) != (*other) }
1053 #[stable(feature = "rust1", since = "1.0.0")]
1054 impl PartialEq for () {
1056 fn eq(&self, _other: &()) -> bool {
1060 fn ne(&self, _other: &()) -> bool {
1066 bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64
1069 macro_rules! eq_impl {
1071 #[stable(feature = "rust1", since = "1.0.0")]
1076 eq_impl! { () bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
1078 macro_rules! partial_ord_impl {
1080 #[stable(feature = "rust1", since = "1.0.0")]
1081 impl PartialOrd for $t {
1083 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
1084 match (self <= other, self >= other) {
1085 (false, false) => None,
1086 (false, true) => Some(Greater),
1087 (true, false) => Some(Less),
1088 (true, true) => Some(Equal),
1092 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
1094 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
1096 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
1098 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
1103 #[stable(feature = "rust1", since = "1.0.0")]
1104 impl PartialOrd for () {
1106 fn partial_cmp(&self, _: &()) -> Option<Ordering> {
1111 #[stable(feature = "rust1", since = "1.0.0")]
1112 impl PartialOrd for bool {
1114 fn partial_cmp(&self, other: &bool) -> Option<Ordering> {
1115 (*self as u8).partial_cmp(&(*other as u8))
1119 partial_ord_impl! { f32 f64 }
1121 macro_rules! ord_impl {
1123 #[stable(feature = "rust1", since = "1.0.0")]
1124 impl PartialOrd for $t {
1126 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
1127 Some(self.cmp(other))
1130 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
1132 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
1134 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
1136 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
1139 #[stable(feature = "rust1", since = "1.0.0")]
1142 fn cmp(&self, other: &$t) -> Ordering {
1143 // The order here is important to generate more optimal assembly.
1144 // See <https://github.com/rust-lang/rust/issues/63758> for more info.
1145 if *self < *other { Less }
1146 else if *self == *other { Equal }
1153 #[stable(feature = "rust1", since = "1.0.0")]
1156 fn cmp(&self, _other: &()) -> Ordering {
1161 #[stable(feature = "rust1", since = "1.0.0")]
1164 fn cmp(&self, other: &bool) -> Ordering {
1165 // Casting to i8's and converting the difference to an Ordering generates
1166 // more optimal assembly.
1167 // See <https://github.com/rust-lang/rust/issues/66780> for more info.
1168 match (*self as i8) - (*other as i8) {
1172 // SAFETY: bool as i8 returns 0 or 1, so the difference can't be anything else
1173 _ => unsafe { unreachable_unchecked() },
1178 ord_impl! { char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
1180 #[unstable(feature = "never_type", issue = "35121")]
1181 impl PartialEq for ! {
1182 fn eq(&self, _: &!) -> bool {
1187 #[unstable(feature = "never_type", issue = "35121")]
1190 #[unstable(feature = "never_type", issue = "35121")]
1191 impl PartialOrd for ! {
1192 fn partial_cmp(&self, _: &!) -> Option<Ordering> {
1197 #[unstable(feature = "never_type", issue = "35121")]
1199 fn cmp(&self, _: &!) -> Ordering {
1206 #[stable(feature = "rust1", since = "1.0.0")]
1207 impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &A
1212 fn eq(&self, other: &&B) -> bool {
1213 PartialEq::eq(*self, *other)
1216 fn ne(&self, other: &&B) -> bool {
1217 PartialEq::ne(*self, *other)
1220 #[stable(feature = "rust1", since = "1.0.0")]
1221 impl<A: ?Sized, B: ?Sized> PartialOrd<&B> for &A
1226 fn partial_cmp(&self, other: &&B) -> Option<Ordering> {
1227 PartialOrd::partial_cmp(*self, *other)
1230 fn lt(&self, other: &&B) -> bool {
1231 PartialOrd::lt(*self, *other)
1234 fn le(&self, other: &&B) -> bool {
1235 PartialOrd::le(*self, *other)
1238 fn gt(&self, other: &&B) -> bool {
1239 PartialOrd::gt(*self, *other)
1242 fn ge(&self, other: &&B) -> bool {
1243 PartialOrd::ge(*self, *other)
1246 #[stable(feature = "rust1", since = "1.0.0")]
1247 impl<A: ?Sized> Ord for &A
1252 fn cmp(&self, other: &Self) -> Ordering {
1253 Ord::cmp(*self, *other)
1256 #[stable(feature = "rust1", since = "1.0.0")]
1257 impl<A: ?Sized> Eq for &A where A: Eq {}
1261 #[stable(feature = "rust1", since = "1.0.0")]
1262 impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &mut A
1267 fn eq(&self, other: &&mut B) -> bool {
1268 PartialEq::eq(*self, *other)
1271 fn ne(&self, other: &&mut B) -> bool {
1272 PartialEq::ne(*self, *other)
1275 #[stable(feature = "rust1", since = "1.0.0")]
1276 impl<A: ?Sized, B: ?Sized> PartialOrd<&mut B> for &mut A
1281 fn partial_cmp(&self, other: &&mut B) -> Option<Ordering> {
1282 PartialOrd::partial_cmp(*self, *other)
1285 fn lt(&self, other: &&mut B) -> bool {
1286 PartialOrd::lt(*self, *other)
1289 fn le(&self, other: &&mut B) -> bool {
1290 PartialOrd::le(*self, *other)
1293 fn gt(&self, other: &&mut B) -> bool {
1294 PartialOrd::gt(*self, *other)
1297 fn ge(&self, other: &&mut B) -> bool {
1298 PartialOrd::ge(*self, *other)
1301 #[stable(feature = "rust1", since = "1.0.0")]
1302 impl<A: ?Sized> Ord for &mut A
1307 fn cmp(&self, other: &Self) -> Ordering {
1308 Ord::cmp(*self, *other)
1311 #[stable(feature = "rust1", since = "1.0.0")]
1312 impl<A: ?Sized> Eq for &mut A where A: Eq {}
1314 #[stable(feature = "rust1", since = "1.0.0")]
1315 impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &A
1320 fn eq(&self, other: &&mut B) -> bool {
1321 PartialEq::eq(*self, *other)
1324 fn ne(&self, other: &&mut B) -> bool {
1325 PartialEq::ne(*self, *other)
1329 #[stable(feature = "rust1", since = "1.0.0")]
1330 impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &mut A
1335 fn eq(&self, other: &&B) -> bool {
1336 PartialEq::eq(*self, *other)
1339 fn ne(&self, other: &&B) -> bool {
1340 PartialEq::ne(*self, *other)