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.
20 //! [`Eq`]: trait.Eq.html
21 //! [`PartialEq`]: trait.PartialEq.html
22 //! [`Ord`]: trait.Ord.html
23 //! [`PartialOrd`]: trait.PartialOrd.html
24 //! [`Ordering`]: enum.Ordering.html
25 //! [`Reverse`]: struct.Reverse.html
26 //! [`max`]: fn.max.html
27 //! [`min`]: fn.min.html
29 #![stable(feature = "rust1", since = "1.0.0")]
31 use self::Ordering::*;
33 /// Trait for equality comparisons which are [partial equivalence
34 /// relations](http://en.wikipedia.org/wiki/Partial_equivalence_relation).
36 /// This trait allows for partial equality, for types that do not have a full
37 /// equivalence relation. For example, in floating point numbers `NaN != NaN`,
38 /// so floating point types implement `PartialEq` but not [`Eq`].
40 /// Formally, the equality must be (for all `a`, `b` and `c`):
42 /// - symmetric: `a == b` implies `b == a`; and
43 /// - transitive: `a == b` and `b == c` implies `a == c`.
45 /// Note that these requirements mean that the trait itself must be implemented
46 /// symmetrically and transitively: if `T: PartialEq<U>` and `U: PartialEq<V>`
47 /// then `U: PartialEq<T>` and `T: PartialEq<V>`.
51 /// This trait can be used with `#[derive]`. When `derive`d on structs, two
52 /// instances are equal if all fields are equal, and not equal if any fields
53 /// are not equal. When `derive`d on enums, each variant is equal to itself
54 /// and not equal to the other variants.
56 /// ## How can I implement `PartialEq`?
58 /// `PartialEq` only requires the [`eq`] method to be implemented; [`ne`] is defined
59 /// in terms of it by default. Any manual implementation of [`ne`] *must* respect
60 /// the rule that [`eq`] is a strict inverse of [`ne`]; that is, `!(a == b)` if and
63 /// Implementations of `PartialEq`, [`PartialOrd`], and [`Ord`] *must* agree with
64 /// each other. It's easy to accidentally make them disagree by deriving some
65 /// of the traits and manually implementing others.
67 /// An example implementation for a domain in which two books are considered
68 /// the same book if their ISBN matches, even if the formats differ:
79 /// format: BookFormat,
82 /// impl PartialEq for Book {
83 /// fn eq(&self, other: &Self) -> bool {
84 /// self.isbn == other.isbn
88 /// let b1 = Book { isbn: 3, format: BookFormat::Paperback };
89 /// let b2 = Book { isbn: 3, format: BookFormat::Ebook };
90 /// let b3 = Book { isbn: 10, format: BookFormat::Paperback };
92 /// assert!(b1 == b2);
93 /// assert!(b1 != b3);
96 /// ## How can I compare two different types?
98 /// The type you can compare with is controlled by `PartialEq`'s type parameter.
99 /// For example, let's tweak our previous code a bit:
102 /// // The derive implements <BookFormat> == <BookFormat> comparisons
103 /// #[derive(PartialEq)]
104 /// enum BookFormat {
112 /// format: BookFormat,
115 /// // Implement <Book> == <BookFormat> comparisons
116 /// impl PartialEq<BookFormat> for Book {
117 /// fn eq(&self, other: &BookFormat) -> bool {
118 /// self.format == *other
122 /// // Implement <BookFormat> == <Book> comparisons
123 /// impl PartialEq<Book> for BookFormat {
124 /// fn eq(&self, other: &Book) -> bool {
125 /// *self == other.format
129 /// let b1 = Book { isbn: 3, format: BookFormat::Paperback };
131 /// assert!(b1 == BookFormat::Paperback);
132 /// assert!(BookFormat::Ebook != b1);
135 /// By changing `impl PartialEq for Book` to `impl PartialEq<BookFormat> for Book`,
136 /// we allow `BookFormat`s to be compared with `Book`s.
138 /// A comparison like the one above, which ignores some fields of the struct,
139 /// can be dangerous. It can easily lead to an unintended violation of the
140 /// requirements for a partial equivalence relation. For example, if we kept
141 /// the above implementation of `PartialEq<Book>` for `BookFormat` and added an
142 /// implementation of `PartialEq<Book>` for `Book` (either via a `#[derive]` or
143 /// via the manual implementation from the first example) then the result would
144 /// violate transitivity:
147 /// #[derive(PartialEq)]
148 /// enum BookFormat {
154 /// #[derive(PartialEq)]
157 /// format: BookFormat,
160 /// impl PartialEq<BookFormat> for Book {
161 /// fn eq(&self, other: &BookFormat) -> bool {
162 /// self.format == *other
166 /// impl PartialEq<Book> for BookFormat {
167 /// fn eq(&self, other: &Book) -> bool {
168 /// *self == other.format
173 /// let b1 = Book { isbn: 1, format: BookFormat::Paperback };
174 /// let b2 = Book { isbn: 2, format: BookFormat::Paperback };
176 /// assert!(b1 == BookFormat::Paperback);
177 /// assert!(BookFormat::Paperback == b2);
179 /// // The following should hold by transitivity but doesn't.
180 /// assert!(b1 == b2); // <-- PANICS
190 /// assert_eq!(x == y, false);
191 /// assert_eq!(x.eq(&y), false);
194 /// [`eq`]: PartialEq::eq
195 /// [`ne`]: PartialEq::ne
197 #[stable(feature = "rust1", since = "1.0.0")]
200 #[rustc_on_unimplemented(
201 message = "can't compare `{Self}` with `{Rhs}`",
202 label = "no implementation for `{Self} == {Rhs}`"
204 pub trait PartialEq<Rhs: ?Sized = Self> {
205 /// This method tests for `self` and `other` values to be equal, and is used
208 #[stable(feature = "rust1", since = "1.0.0")]
209 fn eq(&self, other: &Rhs) -> bool;
211 /// This method tests for `!=`.
214 #[stable(feature = "rust1", since = "1.0.0")]
215 fn ne(&self, other: &Rhs) -> bool {
220 /// Derive macro generating an impl of the trait `PartialEq`.
221 #[rustc_builtin_macro]
222 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
223 #[allow_internal_unstable(core_intrinsics, structural_match)]
224 pub macro PartialEq($item:item) {
225 /* compiler built-in */
228 /// Trait for equality comparisons which are [equivalence relations](
229 /// https://en.wikipedia.org/wiki/Equivalence_relation).
231 /// This means, that in addition to `a == b` and `a != b` being strict inverses, the equality must
232 /// be (for all `a`, `b` and `c`):
234 /// - reflexive: `a == a`;
235 /// - symmetric: `a == b` implies `b == a`; and
236 /// - transitive: `a == b` and `b == c` implies `a == c`.
238 /// This property cannot be checked by the compiler, and therefore `Eq` implies
239 /// [`PartialEq`], and has no extra methods.
243 /// This trait can be used with `#[derive]`. When `derive`d, because `Eq` has
244 /// no extra methods, it is only informing the compiler that this is an
245 /// equivalence relation rather than a partial equivalence relation. Note that
246 /// the `derive` strategy requires all fields are `Eq`, which isn't
249 /// ## How can I implement `Eq`?
251 /// If you cannot use the `derive` strategy, specify that your type implements
252 /// `Eq`, which has no methods:
255 /// enum BookFormat { Paperback, Hardback, Ebook }
258 /// format: BookFormat,
260 /// impl PartialEq for Book {
261 /// fn eq(&self, other: &Self) -> bool {
262 /// self.isbn == other.isbn
265 /// impl Eq for Book {}
269 #[stable(feature = "rust1", since = "1.0.0")]
270 pub trait Eq: PartialEq<Self> {
271 // this method is used solely by #[deriving] to assert
272 // that every component of a type implements #[deriving]
273 // itself, the current deriving infrastructure means doing this
274 // assertion without using a method on this trait is nearly
277 // This should never be implemented by hand.
280 #[stable(feature = "rust1", since = "1.0.0")]
281 fn assert_receiver_is_total_eq(&self) {}
284 /// Derive macro generating an impl of the trait `Eq`.
285 #[rustc_builtin_macro]
286 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
287 #[allow_internal_unstable(core_intrinsics, derive_eq, structural_match)]
288 pub macro Eq($item:item) {
289 /* compiler built-in */
292 // FIXME: this struct is used solely by #[derive] to
293 // assert that every component of a type implements Eq.
295 // This struct should never appear in user code.
297 #[allow(missing_debug_implementations)]
298 #[unstable(feature = "derive_eq", reason = "deriving hack, should not be public", issue = "none")]
299 pub struct AssertParamIsEq<T: Eq + ?Sized> {
300 _field: crate::marker::PhantomData<T>,
303 /// An `Ordering` is the result of a comparison between two values.
308 /// use std::cmp::Ordering;
310 /// let result = 1.cmp(&2);
311 /// assert_eq!(Ordering::Less, result);
313 /// let result = 1.cmp(&1);
314 /// assert_eq!(Ordering::Equal, result);
316 /// let result = 2.cmp(&1);
317 /// assert_eq!(Ordering::Greater, result);
319 #[derive(Clone, Copy, PartialEq, Debug, Hash)]
320 #[stable(feature = "rust1", since = "1.0.0")]
322 /// An ordering where a compared value is less than another.
323 #[stable(feature = "rust1", since = "1.0.0")]
325 /// An ordering where a compared value is equal to another.
326 #[stable(feature = "rust1", since = "1.0.0")]
328 /// An ordering where a compared value is greater than another.
329 #[stable(feature = "rust1", since = "1.0.0")]
334 /// Reverses the `Ordering`.
336 /// * `Less` becomes `Greater`.
337 /// * `Greater` becomes `Less`.
338 /// * `Equal` becomes `Equal`.
345 /// use std::cmp::Ordering;
347 /// assert_eq!(Ordering::Less.reverse(), Ordering::Greater);
348 /// assert_eq!(Ordering::Equal.reverse(), Ordering::Equal);
349 /// assert_eq!(Ordering::Greater.reverse(), Ordering::Less);
352 /// This method can be used to reverse a comparison:
355 /// let data: &mut [_] = &mut [2, 10, 5, 8];
357 /// // sort the array from largest to smallest.
358 /// data.sort_by(|a, b| a.cmp(b).reverse());
360 /// let b: &mut [_] = &mut [10, 8, 5, 2];
361 /// assert!(data == b);
364 #[stable(feature = "rust1", since = "1.0.0")]
365 pub fn reverse(self) -> Ordering {
373 /// Chains two orderings.
375 /// Returns `self` when it's not `Equal`. Otherwise returns `other`.
380 /// use std::cmp::Ordering;
382 /// let result = Ordering::Equal.then(Ordering::Less);
383 /// assert_eq!(result, Ordering::Less);
385 /// let result = Ordering::Less.then(Ordering::Equal);
386 /// assert_eq!(result, Ordering::Less);
388 /// let result = Ordering::Less.then(Ordering::Greater);
389 /// assert_eq!(result, Ordering::Less);
391 /// let result = Ordering::Equal.then(Ordering::Equal);
392 /// assert_eq!(result, Ordering::Equal);
394 /// let x: (i64, i64, i64) = (1, 2, 7);
395 /// let y: (i64, i64, i64) = (1, 5, 3);
396 /// let result = x.0.cmp(&y.0).then(x.1.cmp(&y.1)).then(x.2.cmp(&y.2));
398 /// assert_eq!(result, Ordering::Less);
401 #[stable(feature = "ordering_chaining", since = "1.17.0")]
402 pub fn then(self, other: Ordering) -> Ordering {
409 /// Chains the ordering with the given function.
411 /// Returns `self` when it's not `Equal`. Otherwise calls `f` and returns
417 /// use std::cmp::Ordering;
419 /// let result = Ordering::Equal.then_with(|| Ordering::Less);
420 /// assert_eq!(result, Ordering::Less);
422 /// let result = Ordering::Less.then_with(|| Ordering::Equal);
423 /// assert_eq!(result, Ordering::Less);
425 /// let result = Ordering::Less.then_with(|| Ordering::Greater);
426 /// assert_eq!(result, Ordering::Less);
428 /// let result = Ordering::Equal.then_with(|| Ordering::Equal);
429 /// assert_eq!(result, Ordering::Equal);
431 /// let x: (i64, i64, i64) = (1, 2, 7);
432 /// let y: (i64, i64, i64) = (1, 5, 3);
433 /// let result = x.0.cmp(&y.0).then_with(|| x.1.cmp(&y.1)).then_with(|| x.2.cmp(&y.2));
435 /// assert_eq!(result, Ordering::Less);
438 #[stable(feature = "ordering_chaining", since = "1.17.0")]
439 pub fn then_with<F: FnOnce() -> Ordering>(self, f: F) -> Ordering {
447 /// A helper struct for reverse ordering.
449 /// This struct is a helper to be used with functions like [`Vec::sort_by_key`] and
450 /// can be used to reverse order a part of a key.
452 /// [`Vec::sort_by_key`]: ../../std/vec/struct.Vec.html#method.sort_by_key
457 /// use std::cmp::Reverse;
459 /// let mut v = vec![1, 2, 3, 4, 5, 6];
460 /// v.sort_by_key(|&num| (num > 3, Reverse(num)));
461 /// assert_eq!(v, vec![3, 2, 1, 6, 5, 4]);
463 #[derive(PartialEq, Eq, Debug, Copy, Clone, Default, Hash)]
464 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
465 pub struct Reverse<T>(#[stable(feature = "reverse_cmp_key", since = "1.19.0")] pub T);
467 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
468 impl<T: PartialOrd> PartialOrd for Reverse<T> {
470 fn partial_cmp(&self, other: &Reverse<T>) -> Option<Ordering> {
471 other.0.partial_cmp(&self.0)
475 fn lt(&self, other: &Self) -> bool {
479 fn le(&self, other: &Self) -> bool {
483 fn gt(&self, other: &Self) -> bool {
487 fn ge(&self, other: &Self) -> bool {
492 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
493 impl<T: Ord> Ord for Reverse<T> {
495 fn cmp(&self, other: &Reverse<T>) -> Ordering {
500 /// Trait for types that form a [total order](https://en.wikipedia.org/wiki/Total_order).
502 /// An order is a total order if it is (for all `a`, `b` and `c`):
504 /// - total and asymmetric: exactly one of `a < b`, `a == b` or `a > b` is true; and
505 /// - transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
509 /// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a
510 /// lexicographic ordering based on the top-to-bottom declaration order of the struct's members.
511 /// When `derive`d on enums, variants are ordered by their top-to-bottom declaration order.
513 /// ## How can I implement `Ord`?
515 /// `Ord` requires that the type also be [`PartialOrd`] and [`Eq`] (which requires [`PartialEq`]).
517 /// Then you must define an implementation for [`cmp`]. You may find it useful to use
518 /// [`cmp`] on your type's fields.
520 /// Implementations of [`PartialEq`], [`PartialOrd`], and `Ord` *must*
521 /// agree with each other. That is, `a.cmp(b) == Ordering::Equal` if
522 /// and only if `a == b` and `Some(a.cmp(b)) == a.partial_cmp(b)` for
523 /// all `a` and `b`. It's easy to accidentally make them disagree by
524 /// deriving some of the traits and manually implementing others.
526 /// Here's an example where you want to sort people by height only, disregarding `id`
530 /// use std::cmp::Ordering;
539 /// impl Ord for Person {
540 /// fn cmp(&self, other: &Self) -> Ordering {
541 /// self.height.cmp(&other.height)
545 /// impl PartialOrd for Person {
546 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
547 /// Some(self.cmp(other))
551 /// impl PartialEq for Person {
552 /// fn eq(&self, other: &Self) -> bool {
553 /// self.height == other.height
558 /// [`cmp`]: Ord::cmp
563 #[stable(feature = "rust1", since = "1.0.0")]
564 pub trait Ord: Eq + PartialOrd<Self> {
565 /// This method returns an [`Ordering`] between `self` and `other`.
567 /// By convention, `self.cmp(&other)` returns the ordering matching the expression
568 /// `self <operator> other` if true.
573 /// use std::cmp::Ordering;
575 /// assert_eq!(5.cmp(&10), Ordering::Less);
576 /// assert_eq!(10.cmp(&5), Ordering::Greater);
577 /// assert_eq!(5.cmp(&5), Ordering::Equal);
579 #[stable(feature = "rust1", since = "1.0.0")]
580 fn cmp(&self, other: &Self) -> Ordering;
582 /// Compares and returns the maximum of two values.
584 /// Returns the second argument if the comparison determines them to be equal.
589 /// assert_eq!(2, 1.max(2));
590 /// assert_eq!(2, 2.max(2));
592 #[stable(feature = "ord_max_min", since = "1.21.0")]
594 fn max(self, other: Self) -> Self
598 max_by(self, other, Ord::cmp)
601 /// Compares and returns the minimum of two values.
603 /// Returns the first argument if the comparison determines them to be equal.
608 /// assert_eq!(1, 1.min(2));
609 /// assert_eq!(2, 2.min(2));
611 #[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);
638 #[unstable(feature = "clamp", issue = "44095")]
639 fn clamp(self, min: Self, max: Self) -> Self
646 } else if self > max {
654 /// Derive macro generating an impl of the trait `Ord`.
655 #[rustc_builtin_macro]
656 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
657 #[allow_internal_unstable(core_intrinsics)]
658 pub macro Ord($item:item) {
659 /* compiler built-in */
662 #[stable(feature = "rust1", since = "1.0.0")]
663 impl Eq for Ordering {}
665 #[stable(feature = "rust1", since = "1.0.0")]
666 impl Ord for Ordering {
668 fn cmp(&self, other: &Ordering) -> Ordering {
669 (*self as i32).cmp(&(*other as i32))
673 #[stable(feature = "rust1", since = "1.0.0")]
674 impl PartialOrd for Ordering {
676 fn partial_cmp(&self, other: &Ordering) -> Option<Ordering> {
677 (*self as i32).partial_cmp(&(*other as i32))
681 /// Trait for values that can be compared for a sort-order.
683 /// The comparison must satisfy, for all `a`, `b` and `c`:
685 /// - asymmetry: if `a < b` then `!(a > b)`, as well as `a > b` implying `!(a < b)`; and
686 /// - transitivity: `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
688 /// Note that these requirements mean that the trait itself must be implemented symmetrically and
689 /// transitively: if `T: PartialOrd<U>` and `U: PartialOrd<V>` then `U: PartialOrd<T>` and `T:
694 /// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a
695 /// lexicographic ordering based on the top-to-bottom declaration order of the struct's members.
696 /// When `derive`d on enums, variants are ordered by their top-to-bottom declaration order.
698 /// ## How can I implement `PartialOrd`?
700 /// `PartialOrd` only requires implementation of the [`partial_cmp`] method, with the others
701 /// generated from default implementations.
703 /// However it remains possible to implement the others separately for types which do not have a
704 /// total order. For example, for floating point numbers, `NaN < 0 == false` and `NaN >= 0 ==
705 /// false` (cf. IEEE 754-2008 section 5.11).
707 /// `PartialOrd` requires your type to be [`PartialEq`].
709 /// Implementations of [`PartialEq`], `PartialOrd`, and [`Ord`] *must* agree with each other. It's
710 /// easy to accidentally make them disagree by deriving some of the traits and manually
711 /// implementing others.
713 /// If your type is [`Ord`], you can implement [`partial_cmp`] by using [`cmp`]:
716 /// use std::cmp::Ordering;
725 /// impl PartialOrd for Person {
726 /// fn partial_cmp(&self, other: &Person) -> Option<Ordering> {
727 /// Some(self.cmp(other))
731 /// impl Ord for Person {
732 /// fn cmp(&self, other: &Person) -> Ordering {
733 /// self.height.cmp(&other.height)
737 /// impl PartialEq for Person {
738 /// fn eq(&self, other: &Person) -> bool {
739 /// self.height == other.height
744 /// You may also find it useful to use [`partial_cmp`] on your type's fields. Here
745 /// is an example of `Person` types who have a floating-point `height` field that
746 /// is the only field to be used for sorting:
749 /// use std::cmp::Ordering;
757 /// impl PartialOrd for Person {
758 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
759 /// self.height.partial_cmp(&other.height)
763 /// impl PartialEq for Person {
764 /// fn eq(&self, other: &Self) -> bool {
765 /// self.height == other.height
776 /// assert_eq!(x < y, true);
777 /// assert_eq!(x.lt(&y), true);
780 /// [`partial_cmp`]: PartialOrd::partial_cmp
781 /// [`cmp`]: Ord::cmp
782 #[lang = "partial_ord"]
783 #[stable(feature = "rust1", since = "1.0.0")]
788 #[rustc_on_unimplemented(
789 message = "can't compare `{Self}` with `{Rhs}`",
790 label = "no implementation for `{Self} < {Rhs}` and `{Self} > {Rhs}`"
792 pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
793 /// This method returns an ordering between `self` and `other` values if one exists.
798 /// use std::cmp::Ordering;
800 /// let result = 1.0.partial_cmp(&2.0);
801 /// assert_eq!(result, Some(Ordering::Less));
803 /// let result = 1.0.partial_cmp(&1.0);
804 /// assert_eq!(result, Some(Ordering::Equal));
806 /// let result = 2.0.partial_cmp(&1.0);
807 /// assert_eq!(result, Some(Ordering::Greater));
810 /// When comparison is impossible:
813 /// let result = std::f64::NAN.partial_cmp(&1.0);
814 /// assert_eq!(result, None);
817 #[stable(feature = "rust1", since = "1.0.0")]
818 fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>;
820 /// This method tests less than (for `self` and `other`) and is used by the `<` operator.
825 /// let result = 1.0 < 2.0;
826 /// assert_eq!(result, true);
828 /// let result = 2.0 < 1.0;
829 /// assert_eq!(result, false);
833 #[stable(feature = "rust1", since = "1.0.0")]
834 fn lt(&self, other: &Rhs) -> bool {
835 matches!(self.partial_cmp(other), Some(Less))
838 /// This method tests less than or equal to (for `self` and `other`) and is used by the `<=`
844 /// let result = 1.0 <= 2.0;
845 /// assert_eq!(result, true);
847 /// let result = 2.0 <= 2.0;
848 /// assert_eq!(result, true);
852 #[stable(feature = "rust1", since = "1.0.0")]
853 fn le(&self, other: &Rhs) -> bool {
854 matches!(self.partial_cmp(other), Some(Less) | Some(Equal))
857 /// This method tests greater than (for `self` and `other`) and is used by the `>` operator.
862 /// let result = 1.0 > 2.0;
863 /// assert_eq!(result, false);
865 /// let result = 2.0 > 2.0;
866 /// assert_eq!(result, false);
870 #[stable(feature = "rust1", since = "1.0.0")]
871 fn gt(&self, other: &Rhs) -> bool {
872 matches!(self.partial_cmp(other), Some(Greater))
875 /// This method tests greater than or equal to (for `self` and `other`) and is used by the `>=`
881 /// let result = 2.0 >= 1.0;
882 /// assert_eq!(result, true);
884 /// let result = 2.0 >= 2.0;
885 /// assert_eq!(result, true);
889 #[stable(feature = "rust1", since = "1.0.0")]
890 fn ge(&self, other: &Rhs) -> bool {
891 matches!(self.partial_cmp(other), Some(Greater) | Some(Equal))
895 /// Derive macro generating an impl of the trait `PartialOrd`.
896 #[rustc_builtin_macro]
897 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
898 #[allow_internal_unstable(core_intrinsics)]
899 pub macro PartialOrd($item:item) {
900 /* compiler built-in */
903 /// Compares and returns the minimum of two values.
905 /// Returns the first argument if the comparison determines them to be equal.
907 /// Internally uses an alias to [`Ord::min`].
914 /// assert_eq!(1, cmp::min(1, 2));
915 /// assert_eq!(2, cmp::min(2, 2));
918 #[stable(feature = "rust1", since = "1.0.0")]
919 pub fn min<T: Ord>(v1: T, v2: T) -> T {
923 /// Returns the minimum of two values with respect to the specified comparison function.
925 /// Returns the first argument if the comparison determines them to be equal.
930 /// #![feature(cmp_min_max_by)]
934 /// assert_eq!(cmp::min_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), 1);
935 /// assert_eq!(cmp::min_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), -2);
938 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
939 pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
940 match compare(&v1, &v2) {
941 Ordering::Less | Ordering::Equal => v1,
942 Ordering::Greater => v2,
946 /// Returns the element that gives the minimum value from the specified function.
948 /// Returns the first argument if the comparison determines them to be equal.
953 /// #![feature(cmp_min_max_by)]
957 /// assert_eq!(cmp::min_by_key(-2, 1, |x: &i32| x.abs()), 1);
958 /// assert_eq!(cmp::min_by_key(-2, 2, |x: &i32| x.abs()), -2);
961 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
962 pub fn min_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
963 min_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
966 /// Compares and returns the maximum of two values.
968 /// Returns the second argument if the comparison determines them to be equal.
970 /// Internally uses an alias to [`Ord::max`].
977 /// assert_eq!(2, cmp::max(1, 2));
978 /// assert_eq!(2, cmp::max(2, 2));
981 #[stable(feature = "rust1", since = "1.0.0")]
982 pub fn max<T: Ord>(v1: T, v2: T) -> T {
986 /// Returns the maximum of two values with respect to the specified comparison function.
988 /// Returns the second argument if the comparison determines them to be equal.
993 /// #![feature(cmp_min_max_by)]
997 /// assert_eq!(cmp::max_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), -2);
998 /// assert_eq!(cmp::max_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), 2);
1001 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
1002 pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
1003 match compare(&v1, &v2) {
1004 Ordering::Less | Ordering::Equal => v2,
1005 Ordering::Greater => v1,
1009 /// Returns the element that gives the maximum value from the specified function.
1011 /// Returns the second argument if the comparison determines them to be equal.
1016 /// #![feature(cmp_min_max_by)]
1020 /// assert_eq!(cmp::max_by_key(-2, 1, |x: &i32| x.abs()), -2);
1021 /// assert_eq!(cmp::max_by_key(-2, 2, |x: &i32| x.abs()), 2);
1024 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
1025 pub fn max_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
1026 max_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
1029 // Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types
1031 use crate::cmp::Ordering::{self, Equal, Greater, Less};
1032 use crate::hint::unreachable_unchecked;
1034 macro_rules! partial_eq_impl {
1036 #[stable(feature = "rust1", since = "1.0.0")]
1037 impl PartialEq for $t {
1039 fn eq(&self, other: &$t) -> bool { (*self) == (*other) }
1041 fn ne(&self, other: &$t) -> bool { (*self) != (*other) }
1046 #[stable(feature = "rust1", since = "1.0.0")]
1047 impl PartialEq for () {
1049 fn eq(&self, _other: &()) -> bool {
1053 fn ne(&self, _other: &()) -> bool {
1059 bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64
1062 macro_rules! eq_impl {
1064 #[stable(feature = "rust1", since = "1.0.0")]
1069 eq_impl! { () bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
1071 macro_rules! partial_ord_impl {
1073 #[stable(feature = "rust1", since = "1.0.0")]
1074 impl PartialOrd for $t {
1076 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
1077 match (self <= other, self >= other) {
1078 (false, false) => None,
1079 (false, true) => Some(Greater),
1080 (true, false) => Some(Less),
1081 (true, true) => Some(Equal),
1085 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
1087 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
1089 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
1091 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
1096 #[stable(feature = "rust1", since = "1.0.0")]
1097 impl PartialOrd for () {
1099 fn partial_cmp(&self, _: &()) -> Option<Ordering> {
1104 #[stable(feature = "rust1", since = "1.0.0")]
1105 impl PartialOrd for bool {
1107 fn partial_cmp(&self, other: &bool) -> Option<Ordering> {
1108 (*self as u8).partial_cmp(&(*other as u8))
1112 partial_ord_impl! { f32 f64 }
1114 macro_rules! ord_impl {
1116 #[stable(feature = "rust1", since = "1.0.0")]
1117 impl PartialOrd for $t {
1119 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
1120 Some(self.cmp(other))
1123 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
1125 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
1127 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
1129 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
1132 #[stable(feature = "rust1", since = "1.0.0")]
1135 fn cmp(&self, other: &$t) -> Ordering {
1136 // The order here is important to generate more optimal assembly.
1137 // See <https://github.com/rust-lang/rust/issues/63758> for more info.
1138 if *self < *other { Less }
1139 else if *self == *other { Equal }
1146 #[stable(feature = "rust1", since = "1.0.0")]
1149 fn cmp(&self, _other: &()) -> Ordering {
1154 #[stable(feature = "rust1", since = "1.0.0")]
1157 fn cmp(&self, other: &bool) -> Ordering {
1158 // Casting to i8's and converting the difference to an Ordering generates
1159 // more optimal assembly.
1160 // See <https://github.com/rust-lang/rust/issues/66780> for more info.
1161 match (*self as i8) - (*other as i8) {
1165 // SAFETY: bool as i8 returns 0 or 1, so the difference can't be anything else
1166 _ => unsafe { unreachable_unchecked() },
1171 ord_impl! { char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
1173 #[unstable(feature = "never_type", issue = "35121")]
1174 impl PartialEq for ! {
1175 fn eq(&self, _: &!) -> bool {
1180 #[unstable(feature = "never_type", issue = "35121")]
1183 #[unstable(feature = "never_type", issue = "35121")]
1184 impl PartialOrd for ! {
1185 fn partial_cmp(&self, _: &!) -> Option<Ordering> {
1190 #[unstable(feature = "never_type", issue = "35121")]
1192 fn cmp(&self, _: &!) -> Ordering {
1199 #[stable(feature = "rust1", since = "1.0.0")]
1200 impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &A
1205 fn eq(&self, other: &&B) -> bool {
1206 PartialEq::eq(*self, *other)
1209 fn ne(&self, other: &&B) -> bool {
1210 PartialEq::ne(*self, *other)
1213 #[stable(feature = "rust1", since = "1.0.0")]
1214 impl<A: ?Sized, B: ?Sized> PartialOrd<&B> for &A
1219 fn partial_cmp(&self, other: &&B) -> Option<Ordering> {
1220 PartialOrd::partial_cmp(*self, *other)
1223 fn lt(&self, other: &&B) -> bool {
1224 PartialOrd::lt(*self, *other)
1227 fn le(&self, other: &&B) -> bool {
1228 PartialOrd::le(*self, *other)
1231 fn gt(&self, other: &&B) -> bool {
1232 PartialOrd::gt(*self, *other)
1235 fn ge(&self, other: &&B) -> bool {
1236 PartialOrd::ge(*self, *other)
1239 #[stable(feature = "rust1", since = "1.0.0")]
1240 impl<A: ?Sized> Ord for &A
1245 fn cmp(&self, other: &Self) -> Ordering {
1246 Ord::cmp(*self, *other)
1249 #[stable(feature = "rust1", since = "1.0.0")]
1250 impl<A: ?Sized> Eq for &A where A: Eq {}
1254 #[stable(feature = "rust1", since = "1.0.0")]
1255 impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &mut A
1260 fn eq(&self, other: &&mut B) -> bool {
1261 PartialEq::eq(*self, *other)
1264 fn ne(&self, other: &&mut B) -> bool {
1265 PartialEq::ne(*self, *other)
1268 #[stable(feature = "rust1", since = "1.0.0")]
1269 impl<A: ?Sized, B: ?Sized> PartialOrd<&mut B> for &mut A
1274 fn partial_cmp(&self, other: &&mut B) -> Option<Ordering> {
1275 PartialOrd::partial_cmp(*self, *other)
1278 fn lt(&self, other: &&mut B) -> bool {
1279 PartialOrd::lt(*self, *other)
1282 fn le(&self, other: &&mut B) -> bool {
1283 PartialOrd::le(*self, *other)
1286 fn gt(&self, other: &&mut B) -> bool {
1287 PartialOrd::gt(*self, *other)
1290 fn ge(&self, other: &&mut B) -> bool {
1291 PartialOrd::ge(*self, *other)
1294 #[stable(feature = "rust1", since = "1.0.0")]
1295 impl<A: ?Sized> Ord for &mut A
1300 fn cmp(&self, other: &Self) -> Ordering {
1301 Ord::cmp(*self, *other)
1304 #[stable(feature = "rust1", since = "1.0.0")]
1305 impl<A: ?Sized> Eq for &mut A where A: Eq {}
1307 #[stable(feature = "rust1", since = "1.0.0")]
1308 impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &A
1313 fn eq(&self, other: &&mut B) -> bool {
1314 PartialEq::eq(*self, *other)
1317 fn ne(&self, other: &&mut B) -> bool {
1318 PartialEq::ne(*self, *other)
1322 #[stable(feature = "rust1", since = "1.0.0")]
1323 impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &mut A
1328 fn eq(&self, other: &&B) -> bool {
1329 PartialEq::eq(*self, *other)
1332 fn ne(&self, other: &&B) -> bool {
1333 PartialEq::ne(*self, *other)