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 #[stable(feature = "rust1", since = "1.0.0")]
197 #[rustc_on_unimplemented(
198 message = "can't compare `{Self}` with `{Rhs}`",
199 label = "no implementation for `{Self} == {Rhs}`"
201 pub trait PartialEq<Rhs: ?Sized = Self> {
202 /// This method tests for `self` and `other` values to be equal, and is used
205 #[stable(feature = "rust1", since = "1.0.0")]
206 fn eq(&self, other: &Rhs) -> bool;
208 /// This method tests for `!=`.
211 #[stable(feature = "rust1", since = "1.0.0")]
212 fn ne(&self, other: &Rhs) -> bool {
217 /// Derive macro generating an impl of the trait `PartialEq`.
218 #[rustc_builtin_macro]
219 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
220 #[allow_internal_unstable(core_intrinsics, structural_match)]
221 pub macro PartialEq($item:item) {
222 /* compiler built-in */
225 /// Trait for equality comparisons which are [equivalence relations](
226 /// https://en.wikipedia.org/wiki/Equivalence_relation).
228 /// This means, that in addition to `a == b` and `a != b` being strict inverses, the equality must
229 /// be (for all `a`, `b` and `c`):
231 /// - reflexive: `a == a`;
232 /// - symmetric: `a == b` implies `b == a`; and
233 /// - transitive: `a == b` and `b == c` implies `a == c`.
235 /// This property cannot be checked by the compiler, and therefore `Eq` implies
236 /// `PartialEq`, and has no extra methods.
240 /// This trait can be used with `#[derive]`. When `derive`d, because `Eq` has
241 /// no extra methods, it is only informing the compiler that this is an
242 /// equivalence relation rather than a partial equivalence relation. Note that
243 /// the `derive` strategy requires all fields are `Eq`, which isn't
246 /// ## How can I implement `Eq`?
248 /// If you cannot use the `derive` strategy, specify that your type implements
249 /// `Eq`, which has no methods:
252 /// enum BookFormat { Paperback, Hardback, Ebook }
255 /// format: BookFormat,
257 /// impl PartialEq for Book {
258 /// fn eq(&self, other: &Self) -> bool {
259 /// self.isbn == other.isbn
262 /// impl Eq for Book {}
266 #[stable(feature = "rust1", since = "1.0.0")]
267 pub trait Eq: PartialEq<Self> {
268 // this method is used solely by #[deriving] to assert
269 // that every component of a type implements #[deriving]
270 // itself, the current deriving infrastructure means doing this
271 // assertion without using a method on this trait is nearly
274 // This should never be implemented by hand.
277 #[stable(feature = "rust1", since = "1.0.0")]
278 fn assert_receiver_is_total_eq(&self) {}
281 /// Derive macro generating an impl of the trait `Eq`.
282 #[rustc_builtin_macro]
283 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
284 #[allow_internal_unstable(core_intrinsics, derive_eq, structural_match)]
285 pub macro Eq($item:item) {
286 /* compiler built-in */
289 // FIXME: this struct is used solely by #[derive] to
290 // assert that every component of a type implements Eq.
292 // This struct should never appear in user code.
294 #[allow(missing_debug_implementations)]
295 #[unstable(feature = "derive_eq", reason = "deriving hack, should not be public", issue = "none")]
296 pub struct AssertParamIsEq<T: Eq + ?Sized> {
297 _field: crate::marker::PhantomData<T>,
300 /// An `Ordering` is the result of a comparison between two values.
305 /// use std::cmp::Ordering;
307 /// let result = 1.cmp(&2);
308 /// assert_eq!(Ordering::Less, result);
310 /// let result = 1.cmp(&1);
311 /// assert_eq!(Ordering::Equal, result);
313 /// let result = 2.cmp(&1);
314 /// assert_eq!(Ordering::Greater, result);
316 #[derive(Clone, Copy, PartialEq, Debug, Hash)]
317 #[stable(feature = "rust1", since = "1.0.0")]
319 /// An ordering where a compared value is less than another.
320 #[stable(feature = "rust1", since = "1.0.0")]
322 /// An ordering where a compared value is equal to another.
323 #[stable(feature = "rust1", since = "1.0.0")]
325 /// An ordering where a compared value is greater than another.
326 #[stable(feature = "rust1", since = "1.0.0")]
331 /// Reverses the `Ordering`.
333 /// * `Less` becomes `Greater`.
334 /// * `Greater` becomes `Less`.
335 /// * `Equal` becomes `Equal`.
342 /// use std::cmp::Ordering;
344 /// assert_eq!(Ordering::Less.reverse(), Ordering::Greater);
345 /// assert_eq!(Ordering::Equal.reverse(), Ordering::Equal);
346 /// assert_eq!(Ordering::Greater.reverse(), Ordering::Less);
349 /// This method can be used to reverse a comparison:
352 /// let data: &mut [_] = &mut [2, 10, 5, 8];
354 /// // sort the array from largest to smallest.
355 /// data.sort_by(|a, b| a.cmp(b).reverse());
357 /// let b: &mut [_] = &mut [10, 8, 5, 2];
358 /// assert!(data == b);
361 #[stable(feature = "rust1", since = "1.0.0")]
362 pub fn reverse(self) -> Ordering {
370 /// Chains two orderings.
372 /// 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);
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);
434 #[stable(feature = "ordering_chaining", since = "1.17.0")]
435 pub fn then_with<F: FnOnce() -> Ordering>(self, f: F) -> Ordering {
443 /// A helper struct for reverse ordering.
445 /// This struct is a helper to be used with functions like `Vec::sort_by_key` and
446 /// can be used to reverse order a part of a key.
451 /// use std::cmp::Reverse;
453 /// let mut v = vec![1, 2, 3, 4, 5, 6];
454 /// v.sort_by_key(|&num| (num > 3, Reverse(num)));
455 /// assert_eq!(v, vec![3, 2, 1, 6, 5, 4]);
457 #[derive(PartialEq, Eq, Debug, Copy, Clone, Default, Hash)]
458 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
459 pub struct Reverse<T>(#[stable(feature = "reverse_cmp_key", since = "1.19.0")] pub T);
461 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
462 impl<T: PartialOrd> PartialOrd for Reverse<T> {
464 fn partial_cmp(&self, other: &Reverse<T>) -> Option<Ordering> {
465 other.0.partial_cmp(&self.0)
469 fn lt(&self, other: &Self) -> bool {
473 fn le(&self, other: &Self) -> bool {
477 fn gt(&self, other: &Self) -> bool {
481 fn ge(&self, other: &Self) -> bool {
486 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
487 impl<T: Ord> Ord for Reverse<T> {
489 fn cmp(&self, other: &Reverse<T>) -> Ordering {
494 /// Trait for types that form a [total order](https://en.wikipedia.org/wiki/Total_order).
496 /// An order is a total order if it is (for all `a`, `b` and `c`):
498 /// - total and asymmetric: exactly one of `a < b`, `a == b` or `a > b` is true; and
499 /// - transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
503 /// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a
504 /// lexicographic ordering based on the top-to-bottom declaration order of the struct's members.
505 /// When `derive`d on enums, variants are ordered by their top-to-bottom declaration order.
507 /// ## How can I implement `Ord`?
509 /// `Ord` requires that the type also be `PartialOrd` and `Eq` (which requires `PartialEq`).
511 /// Then you must define an implementation for `cmp()`. You may find it useful to use
512 /// `cmp()` on your type's fields.
514 /// Implementations of `PartialEq`, `PartialOrd`, and `Ord` *must*
515 /// agree with each other. That is, `a.cmp(b) == Ordering::Equal` if
516 /// and only if `a == b` and `Some(a.cmp(b)) == a.partial_cmp(b)` for
517 /// all `a` and `b`. It's easy to accidentally make them disagree by
518 /// deriving some of the traits and manually implementing others.
520 /// Here's an example where you want to sort people by height only, disregarding `id`
524 /// use std::cmp::Ordering;
533 /// impl Ord for Person {
534 /// fn cmp(&self, other: &Self) -> Ordering {
535 /// self.height.cmp(&other.height)
539 /// impl PartialOrd for Person {
540 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
541 /// Some(self.cmp(other))
545 /// impl PartialEq for Person {
546 /// fn eq(&self, other: &Self) -> bool {
547 /// self.height == other.height
555 #[stable(feature = "rust1", since = "1.0.0")]
556 pub trait Ord: Eq + PartialOrd<Self> {
557 /// This method returns an `Ordering` between `self` and `other`.
559 /// By convention, `self.cmp(&other)` returns the ordering matching the expression
560 /// `self <operator> other` if true.
565 /// use std::cmp::Ordering;
567 /// assert_eq!(5.cmp(&10), Ordering::Less);
568 /// assert_eq!(10.cmp(&5), Ordering::Greater);
569 /// assert_eq!(5.cmp(&5), Ordering::Equal);
571 #[stable(feature = "rust1", since = "1.0.0")]
572 fn cmp(&self, other: &Self) -> Ordering;
574 /// Compares and returns the maximum of two values.
576 /// Returns the second argument if the comparison determines them to be equal.
581 /// assert_eq!(2, 1.max(2));
582 /// assert_eq!(2, 2.max(2));
584 #[stable(feature = "ord_max_min", since = "1.21.0")]
586 fn max(self, other: Self) -> Self
590 max_by(self, other, Ord::cmp)
593 /// Compares and returns the minimum of two values.
595 /// Returns the first argument if the comparison determines them to be equal.
600 /// assert_eq!(1, 1.min(2));
601 /// assert_eq!(2, 2.min(2));
603 #[stable(feature = "ord_max_min", since = "1.21.0")]
605 fn min(self, other: Self) -> Self
609 min_by(self, other, Ord::cmp)
612 /// Restrict a value to a certain interval.
614 /// Returns `max` if `self` is greater than `max`, and `min` if `self` is
615 /// less than `min`. Otherwise this returns `self`.
619 /// Panics if `min > max`.
624 /// #![feature(clamp)]
626 /// assert!((-3).clamp(-2, 1) == -2);
627 /// assert!(0.clamp(-2, 1) == 0);
628 /// assert!(2.clamp(-2, 1) == 1);
630 #[unstable(feature = "clamp", issue = "44095")]
631 fn clamp(self, min: Self, max: Self) -> Self
638 } else if self > max {
646 /// Derive macro generating an impl of the trait `Ord`.
647 #[rustc_builtin_macro]
648 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
649 #[allow_internal_unstable(core_intrinsics)]
650 pub macro Ord($item:item) {
651 /* compiler built-in */
654 #[stable(feature = "rust1", since = "1.0.0")]
655 impl Eq for Ordering {}
657 #[stable(feature = "rust1", since = "1.0.0")]
658 impl Ord for Ordering {
660 fn cmp(&self, other: &Ordering) -> Ordering {
661 (*self as i32).cmp(&(*other as i32))
665 #[stable(feature = "rust1", since = "1.0.0")]
666 impl PartialOrd for Ordering {
668 fn partial_cmp(&self, other: &Ordering) -> Option<Ordering> {
669 (*self as i32).partial_cmp(&(*other as i32))
673 /// Trait for values that can be compared for a sort-order.
675 /// The comparison must satisfy, for all `a`, `b` and `c`:
677 /// - asymmetry: if `a < b` then `!(a > b)`, as well as `a > b` implying `!(a < b)`; and
678 /// - transitivity: `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
680 /// Note that these requirements mean that the trait itself must be implemented symmetrically and
681 /// transitively: if `T: PartialOrd<U>` and `U: PartialOrd<V>` then `U: PartialOrd<T>` and `T:
686 /// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a
687 /// lexicographic ordering based on the top-to-bottom declaration order of the struct's members.
688 /// When `derive`d on enums, variants are ordered by their top-to-bottom declaration order.
690 /// ## How can I implement `PartialOrd`?
692 /// `PartialOrd` only requires implementation of the `partial_cmp` method, with the others
693 /// generated from default implementations.
695 /// However it remains possible to implement the others separately for types which do not have a
696 /// total order. For example, for floating point numbers, `NaN < 0 == false` and `NaN >= 0 ==
697 /// false` (cf. IEEE 754-2008 section 5.11).
699 /// `PartialOrd` requires your type to be `PartialEq`.
701 /// Implementations of `PartialEq`, `PartialOrd`, and `Ord` *must* agree with each other. It's
702 /// easy to accidentally make them disagree by deriving some of the traits and manually
703 /// implementing others.
705 /// If your type is `Ord`, you can implement `partial_cmp()` by using `cmp()`:
708 /// use std::cmp::Ordering;
717 /// impl PartialOrd for Person {
718 /// fn partial_cmp(&self, other: &Person) -> Option<Ordering> {
719 /// Some(self.cmp(other))
723 /// impl Ord for Person {
724 /// fn cmp(&self, other: &Person) -> Ordering {
725 /// self.height.cmp(&other.height)
729 /// impl PartialEq for Person {
730 /// fn eq(&self, other: &Person) -> bool {
731 /// self.height == other.height
736 /// You may also find it useful to use `partial_cmp()` on your type's fields. Here
737 /// is an example of `Person` types who have a floating-point `height` field that
738 /// is the only field to be used for sorting:
741 /// use std::cmp::Ordering;
749 /// impl PartialOrd for Person {
750 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
751 /// self.height.partial_cmp(&other.height)
755 /// impl PartialEq for Person {
756 /// fn eq(&self, other: &Self) -> bool {
757 /// self.height == other.height
768 /// assert_eq!(x < y, true);
769 /// assert_eq!(x.lt(&y), true);
771 #[lang = "partial_ord"]
772 #[stable(feature = "rust1", since = "1.0.0")]
777 #[rustc_on_unimplemented(
778 message = "can't compare `{Self}` with `{Rhs}`",
779 label = "no implementation for `{Self} < {Rhs}` and `{Self} > {Rhs}`"
781 pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
782 /// This method returns an ordering between `self` and `other` values if one exists.
787 /// use std::cmp::Ordering;
789 /// let result = 1.0.partial_cmp(&2.0);
790 /// assert_eq!(result, Some(Ordering::Less));
792 /// let result = 1.0.partial_cmp(&1.0);
793 /// assert_eq!(result, Some(Ordering::Equal));
795 /// let result = 2.0.partial_cmp(&1.0);
796 /// assert_eq!(result, Some(Ordering::Greater));
799 /// When comparison is impossible:
802 /// let result = std::f64::NAN.partial_cmp(&1.0);
803 /// assert_eq!(result, None);
806 #[stable(feature = "rust1", since = "1.0.0")]
807 fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>;
809 /// This method tests less than (for `self` and `other`) and is used by the `<` operator.
814 /// let result = 1.0 < 2.0;
815 /// assert_eq!(result, true);
817 /// let result = 2.0 < 1.0;
818 /// assert_eq!(result, false);
822 #[stable(feature = "rust1", since = "1.0.0")]
823 fn lt(&self, other: &Rhs) -> bool {
824 matches!(self.partial_cmp(other), Some(Less))
827 /// This method tests less than or equal to (for `self` and `other`) and is used by the `<=`
833 /// let result = 1.0 <= 2.0;
834 /// assert_eq!(result, true);
836 /// let result = 2.0 <= 2.0;
837 /// assert_eq!(result, true);
841 #[stable(feature = "rust1", since = "1.0.0")]
842 fn le(&self, other: &Rhs) -> bool {
843 matches!(self.partial_cmp(other), Some(Less) | Some(Equal))
846 /// This method tests greater than (for `self` and `other`) and is used by the `>` operator.
851 /// let result = 1.0 > 2.0;
852 /// assert_eq!(result, false);
854 /// let result = 2.0 > 2.0;
855 /// assert_eq!(result, false);
859 #[stable(feature = "rust1", since = "1.0.0")]
860 fn gt(&self, other: &Rhs) -> bool {
861 matches!(self.partial_cmp(other), Some(Greater))
864 /// This method tests greater than or equal to (for `self` and `other`) and is used by the `>=`
870 /// let result = 2.0 >= 1.0;
871 /// assert_eq!(result, true);
873 /// let result = 2.0 >= 2.0;
874 /// assert_eq!(result, true);
878 #[stable(feature = "rust1", since = "1.0.0")]
879 fn ge(&self, other: &Rhs) -> bool {
880 matches!(self.partial_cmp(other), Some(Greater) | Some(Equal))
884 /// Derive macro generating an impl of the trait `PartialOrd`.
885 #[rustc_builtin_macro]
886 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
887 #[allow_internal_unstable(core_intrinsics)]
888 pub macro PartialOrd($item:item) {
889 /* compiler built-in */
892 /// Compares and returns the minimum of two values.
894 /// Returns the first argument if the comparison determines them to be equal.
896 /// Internally uses an alias to `Ord::min`.
903 /// assert_eq!(1, cmp::min(1, 2));
904 /// assert_eq!(2, cmp::min(2, 2));
907 #[stable(feature = "rust1", since = "1.0.0")]
908 pub fn min<T: Ord>(v1: T, v2: T) -> T {
912 /// Returns the minimum of two values with respect to the specified comparison function.
914 /// Returns the first argument if the comparison determines them to be equal.
919 /// #![feature(cmp_min_max_by)]
923 /// assert_eq!(cmp::min_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), 1);
924 /// assert_eq!(cmp::min_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), -2);
927 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
928 pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
929 match compare(&v1, &v2) {
930 Ordering::Less | Ordering::Equal => v1,
931 Ordering::Greater => v2,
935 /// Returns the element that gives the minimum value from the specified 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_key(-2, 1, |x: &i32| x.abs()), 1);
947 /// assert_eq!(cmp::min_by_key(-2, 2, |x: &i32| x.abs()), -2);
950 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
951 pub fn min_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
952 min_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
955 /// Compares and returns the maximum of two values.
957 /// Returns the second argument if the comparison determines them to be equal.
959 /// Internally uses an alias to `Ord::max`.
966 /// assert_eq!(2, cmp::max(1, 2));
967 /// assert_eq!(2, cmp::max(2, 2));
970 #[stable(feature = "rust1", since = "1.0.0")]
971 pub fn max<T: Ord>(v1: T, v2: T) -> T {
975 /// Returns the maximum of two values with respect to the specified comparison function.
977 /// Returns the second argument if the comparison determines them to be equal.
982 /// #![feature(cmp_min_max_by)]
986 /// assert_eq!(cmp::max_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), -2);
987 /// assert_eq!(cmp::max_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), 2);
990 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
991 pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
992 match compare(&v1, &v2) {
993 Ordering::Less | Ordering::Equal => v2,
994 Ordering::Greater => v1,
998 /// Returns the element that gives the maximum value from the specified function.
1000 /// Returns the second argument if the comparison determines them to be equal.
1005 /// #![feature(cmp_min_max_by)]
1009 /// assert_eq!(cmp::max_by_key(-2, 1, |x: &i32| x.abs()), -2);
1010 /// assert_eq!(cmp::max_by_key(-2, 2, |x: &i32| x.abs()), 2);
1013 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
1014 pub fn max_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
1015 max_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
1018 // Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types
1020 use crate::cmp::Ordering::{self, Equal, Greater, Less};
1021 use crate::hint::unreachable_unchecked;
1023 macro_rules! partial_eq_impl {
1025 #[stable(feature = "rust1", since = "1.0.0")]
1026 impl PartialEq for $t {
1028 fn eq(&self, other: &$t) -> bool { (*self) == (*other) }
1030 fn ne(&self, other: &$t) -> bool { (*self) != (*other) }
1035 #[stable(feature = "rust1", since = "1.0.0")]
1036 impl PartialEq for () {
1038 fn eq(&self, _other: &()) -> bool {
1042 fn ne(&self, _other: &()) -> bool {
1048 bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64
1051 macro_rules! eq_impl {
1053 #[stable(feature = "rust1", since = "1.0.0")]
1058 eq_impl! { () bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
1060 macro_rules! partial_ord_impl {
1062 #[stable(feature = "rust1", since = "1.0.0")]
1063 impl PartialOrd for $t {
1065 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
1066 match (self <= other, self >= other) {
1067 (false, false) => None,
1068 (false, true) => Some(Greater),
1069 (true, false) => Some(Less),
1070 (true, true) => Some(Equal),
1074 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
1076 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
1078 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
1080 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
1085 #[stable(feature = "rust1", since = "1.0.0")]
1086 impl PartialOrd for () {
1088 fn partial_cmp(&self, _: &()) -> Option<Ordering> {
1093 #[stable(feature = "rust1", since = "1.0.0")]
1094 impl PartialOrd for bool {
1096 fn partial_cmp(&self, other: &bool) -> Option<Ordering> {
1097 (*self as u8).partial_cmp(&(*other as u8))
1101 partial_ord_impl! { f32 f64 }
1103 macro_rules! ord_impl {
1105 #[stable(feature = "rust1", since = "1.0.0")]
1106 impl PartialOrd for $t {
1108 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
1109 Some(self.cmp(other))
1112 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
1114 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
1116 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
1118 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
1121 #[stable(feature = "rust1", since = "1.0.0")]
1124 fn cmp(&self, other: &$t) -> Ordering {
1125 // The order here is important to generate more optimal assembly.
1126 // See <https://github.com/rust-lang/rust/issues/63758> for more info.
1127 if *self < *other { Less }
1128 else if *self == *other { Equal }
1135 #[stable(feature = "rust1", since = "1.0.0")]
1138 fn cmp(&self, _other: &()) -> Ordering {
1143 #[stable(feature = "rust1", since = "1.0.0")]
1146 fn cmp(&self, other: &bool) -> Ordering {
1147 // Casting to i8's and converting the difference to an Ordering generates
1148 // more optimal assembly.
1149 // See <https://github.com/rust-lang/rust/issues/66780> for more info.
1150 match (*self as i8) - (*other as i8) {
1154 // SAFETY: bool as i8 returns 0 or 1, so the difference can't be anything else
1155 _ => unsafe { unreachable_unchecked() },
1160 ord_impl! { char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
1162 #[unstable(feature = "never_type", issue = "35121")]
1163 impl PartialEq for ! {
1164 fn eq(&self, _: &!) -> bool {
1169 #[unstable(feature = "never_type", issue = "35121")]
1172 #[unstable(feature = "never_type", issue = "35121")]
1173 impl PartialOrd for ! {
1174 fn partial_cmp(&self, _: &!) -> Option<Ordering> {
1179 #[unstable(feature = "never_type", issue = "35121")]
1181 fn cmp(&self, _: &!) -> Ordering {
1188 #[stable(feature = "rust1", since = "1.0.0")]
1189 impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &A
1194 fn eq(&self, other: &&B) -> bool {
1195 PartialEq::eq(*self, *other)
1198 fn ne(&self, other: &&B) -> bool {
1199 PartialEq::ne(*self, *other)
1202 #[stable(feature = "rust1", since = "1.0.0")]
1203 impl<A: ?Sized, B: ?Sized> PartialOrd<&B> for &A
1208 fn partial_cmp(&self, other: &&B) -> Option<Ordering> {
1209 PartialOrd::partial_cmp(*self, *other)
1212 fn lt(&self, other: &&B) -> bool {
1213 PartialOrd::lt(*self, *other)
1216 fn le(&self, other: &&B) -> bool {
1217 PartialOrd::le(*self, *other)
1220 fn gt(&self, other: &&B) -> bool {
1221 PartialOrd::gt(*self, *other)
1224 fn ge(&self, other: &&B) -> bool {
1225 PartialOrd::ge(*self, *other)
1228 #[stable(feature = "rust1", since = "1.0.0")]
1229 impl<A: ?Sized> Ord for &A
1234 fn cmp(&self, other: &Self) -> Ordering {
1235 Ord::cmp(*self, *other)
1238 #[stable(feature = "rust1", since = "1.0.0")]
1239 impl<A: ?Sized> Eq for &A where A: Eq {}
1243 #[stable(feature = "rust1", since = "1.0.0")]
1244 impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &mut A
1249 fn eq(&self, other: &&mut B) -> bool {
1250 PartialEq::eq(*self, *other)
1253 fn ne(&self, other: &&mut B) -> bool {
1254 PartialEq::ne(*self, *other)
1257 #[stable(feature = "rust1", since = "1.0.0")]
1258 impl<A: ?Sized, B: ?Sized> PartialOrd<&mut B> for &mut A
1263 fn partial_cmp(&self, other: &&mut B) -> Option<Ordering> {
1264 PartialOrd::partial_cmp(*self, *other)
1267 fn lt(&self, other: &&mut B) -> bool {
1268 PartialOrd::lt(*self, *other)
1271 fn le(&self, other: &&mut B) -> bool {
1272 PartialOrd::le(*self, *other)
1275 fn gt(&self, other: &&mut B) -> bool {
1276 PartialOrd::gt(*self, *other)
1279 fn ge(&self, other: &&mut B) -> bool {
1280 PartialOrd::ge(*self, *other)
1283 #[stable(feature = "rust1", since = "1.0.0")]
1284 impl<A: ?Sized> Ord for &mut A
1289 fn cmp(&self, other: &Self) -> Ordering {
1290 Ord::cmp(*self, *other)
1293 #[stable(feature = "rust1", since = "1.0.0")]
1294 impl<A: ?Sized> Eq for &mut A where A: Eq {}
1296 #[stable(feature = "rust1", since = "1.0.0")]
1297 impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &A
1302 fn eq(&self, other: &&mut B) -> bool {
1303 PartialEq::eq(*self, *other)
1306 fn ne(&self, other: &&mut B) -> bool {
1307 PartialEq::ne(*self, *other)
1311 #[stable(feature = "rust1", since = "1.0.0")]
1312 impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &mut A
1317 fn eq(&self, other: &&B) -> bool {
1318 PartialEq::eq(*self, *other)
1321 fn ne(&self, other: &&B) -> bool {
1322 PartialEq::ne(*self, *other)