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 { !self.eq(other) }
215 /// Derive macro generating an impl of the trait `PartialEq`.
216 #[rustc_builtin_macro]
217 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
218 #[allow_internal_unstable(core_intrinsics, structural_match)]
219 pub macro PartialEq($item:item) { /* compiler built-in */ }
221 /// Trait for equality comparisons which are [equivalence relations](
222 /// https://en.wikipedia.org/wiki/Equivalence_relation).
224 /// This means, that in addition to `a == b` and `a != b` being strict inverses, the equality must
225 /// be (for all `a`, `b` and `c`):
227 /// - reflexive: `a == a`;
228 /// - symmetric: `a == b` implies `b == a`; and
229 /// - transitive: `a == b` and `b == c` implies `a == c`.
231 /// This property cannot be checked by the compiler, and therefore `Eq` implies
232 /// `PartialEq`, and has no extra methods.
236 /// This trait can be used with `#[derive]`. When `derive`d, because `Eq` has
237 /// no extra methods, it is only informing the compiler that this is an
238 /// equivalence relation rather than a partial equivalence relation. Note that
239 /// the `derive` strategy requires all fields are `Eq`, which isn't
242 /// ## How can I implement `Eq`?
244 /// If you cannot use the `derive` strategy, specify that your type implements
245 /// `Eq`, which has no methods:
248 /// enum BookFormat { Paperback, Hardback, Ebook }
251 /// format: BookFormat,
253 /// impl PartialEq for Book {
254 /// fn eq(&self, other: &Self) -> bool {
255 /// self.isbn == other.isbn
258 /// impl Eq for Book {}
262 #[stable(feature = "rust1", since = "1.0.0")]
263 pub trait Eq: PartialEq<Self> {
264 // this method is used solely by #[deriving] to assert
265 // that every component of a type implements #[deriving]
266 // itself, the current deriving infrastructure means doing this
267 // assertion without using a method on this trait is nearly
270 // This should never be implemented by hand.
273 #[stable(feature = "rust1", since = "1.0.0")]
274 fn assert_receiver_is_total_eq(&self) {}
277 /// Derive macro generating an impl of the trait `Eq`.
278 #[rustc_builtin_macro]
279 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
280 #[allow_internal_unstable(core_intrinsics, derive_eq, structural_match)]
281 pub macro Eq($item:item) { /* compiler built-in */ }
283 // FIXME: this struct is used solely by #[derive] to
284 // assert that every component of a type implements Eq.
286 // This struct should never appear in user code.
288 #[allow(missing_debug_implementations)]
289 #[unstable(feature = "derive_eq",
290 reason = "deriving hack, should not be public",
292 pub struct AssertParamIsEq<T: Eq + ?Sized> { _field: crate::marker::PhantomData<T> }
294 /// An `Ordering` is the result of a comparison between two values.
299 /// use std::cmp::Ordering;
301 /// let result = 1.cmp(&2);
302 /// assert_eq!(Ordering::Less, result);
304 /// let result = 1.cmp(&1);
305 /// assert_eq!(Ordering::Equal, result);
307 /// let result = 2.cmp(&1);
308 /// assert_eq!(Ordering::Greater, result);
310 #[derive(Clone, Copy, PartialEq, Debug, Hash)]
311 #[stable(feature = "rust1", since = "1.0.0")]
313 /// An ordering where a compared value is less than another.
314 #[stable(feature = "rust1", since = "1.0.0")]
316 /// An ordering where a compared value is equal to another.
317 #[stable(feature = "rust1", since = "1.0.0")]
319 /// An ordering where a compared value is greater than another.
320 #[stable(feature = "rust1", since = "1.0.0")]
325 /// Reverses the `Ordering`.
327 /// * `Less` becomes `Greater`.
328 /// * `Greater` becomes `Less`.
329 /// * `Equal` becomes `Equal`.
336 /// use std::cmp::Ordering;
338 /// assert_eq!(Ordering::Less.reverse(), Ordering::Greater);
339 /// assert_eq!(Ordering::Equal.reverse(), Ordering::Equal);
340 /// assert_eq!(Ordering::Greater.reverse(), Ordering::Less);
343 /// This method can be used to reverse a comparison:
346 /// let data: &mut [_] = &mut [2, 10, 5, 8];
348 /// // sort the array from largest to smallest.
349 /// data.sort_by(|a, b| a.cmp(b).reverse());
351 /// let b: &mut [_] = &mut [10, 8, 5, 2];
352 /// assert!(data == b);
355 #[stable(feature = "rust1", since = "1.0.0")]
356 pub fn reverse(self) -> Ordering {
364 /// Chains two orderings.
366 /// Returns `self` when it's not `Equal`. Otherwise returns `other`.
370 /// use std::cmp::Ordering;
372 /// let result = Ordering::Equal.then(Ordering::Less);
373 /// assert_eq!(result, Ordering::Less);
375 /// let result = Ordering::Less.then(Ordering::Equal);
376 /// assert_eq!(result, Ordering::Less);
378 /// let result = Ordering::Less.then(Ordering::Greater);
379 /// assert_eq!(result, Ordering::Less);
381 /// let result = Ordering::Equal.then(Ordering::Equal);
382 /// assert_eq!(result, Ordering::Equal);
384 /// let x: (i64, i64, i64) = (1, 2, 7);
385 /// let y: (i64, i64, i64) = (1, 5, 3);
386 /// let result = x.0.cmp(&y.0).then(x.1.cmp(&y.1)).then(x.2.cmp(&y.2));
388 /// assert_eq!(result, Ordering::Less);
391 #[stable(feature = "ordering_chaining", since = "1.17.0")]
392 pub fn then(self, other: Ordering) -> Ordering {
399 /// Chains the ordering with the given function.
401 /// Returns `self` when it's not `Equal`. Otherwise calls `f` and returns
407 /// use std::cmp::Ordering;
409 /// let result = Ordering::Equal.then_with(|| Ordering::Less);
410 /// assert_eq!(result, Ordering::Less);
412 /// let result = Ordering::Less.then_with(|| Ordering::Equal);
413 /// assert_eq!(result, Ordering::Less);
415 /// let result = Ordering::Less.then_with(|| Ordering::Greater);
416 /// assert_eq!(result, Ordering::Less);
418 /// let result = Ordering::Equal.then_with(|| Ordering::Equal);
419 /// assert_eq!(result, Ordering::Equal);
421 /// let x: (i64, i64, i64) = (1, 2, 7);
422 /// let y: (i64, i64, i64) = (1, 5, 3);
423 /// let result = x.0.cmp(&y.0).then_with(|| x.1.cmp(&y.1)).then_with(|| x.2.cmp(&y.2));
425 /// assert_eq!(result, Ordering::Less);
428 #[stable(feature = "ordering_chaining", since = "1.17.0")]
429 pub fn then_with<F: FnOnce() -> Ordering>(self, f: F) -> Ordering {
437 /// A helper struct for reverse ordering.
439 /// This struct is a helper to be used with functions like `Vec::sort_by_key` and
440 /// can be used to reverse order a part of a key.
445 /// use std::cmp::Reverse;
447 /// let mut v = vec![1, 2, 3, 4, 5, 6];
448 /// v.sort_by_key(|&num| (num > 3, Reverse(num)));
449 /// assert_eq!(v, vec![3, 2, 1, 6, 5, 4]);
451 #[derive(PartialEq, Eq, Debug, Copy, Clone, Default, Hash)]
452 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
453 pub struct Reverse<T>(#[stable(feature = "reverse_cmp_key", since = "1.19.0")] pub T);
455 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
456 impl<T: PartialOrd> PartialOrd for Reverse<T> {
458 fn partial_cmp(&self, other: &Reverse<T>) -> Option<Ordering> {
459 other.0.partial_cmp(&self.0)
463 fn lt(&self, other: &Self) -> bool { other.0 < self.0 }
465 fn le(&self, other: &Self) -> bool { other.0 <= self.0 }
467 fn gt(&self, other: &Self) -> bool { other.0 > self.0 }
469 fn ge(&self, other: &Self) -> bool { other.0 >= self.0 }
472 #[stable(feature = "reverse_cmp_key", since = "1.19.0")]
473 impl<T: Ord> Ord for Reverse<T> {
475 fn cmp(&self, other: &Reverse<T>) -> Ordering {
480 /// Trait for types that form a [total order](https://en.wikipedia.org/wiki/Total_order).
482 /// An order is a total order if it is (for all `a`, `b` and `c`):
484 /// - total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true; and
485 /// - transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
489 /// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a
490 /// lexicographic ordering based on the top-to-bottom declaration order of the struct's members.
491 /// When `derive`d on enums, variants are ordered by their top-to-bottom declaration order.
493 /// ## How can I implement `Ord`?
495 /// `Ord` requires that the type also be `PartialOrd` and `Eq` (which requires `PartialEq`).
497 /// Then you must define an implementation for `cmp()`. You may find it useful to use
498 /// `cmp()` on your type's fields.
500 /// Implementations of `PartialEq`, `PartialOrd`, and `Ord` *must*
501 /// agree with each other. That is, `a.cmp(b) == Ordering::Equal` if
502 /// and only if `a == b` and `Some(a.cmp(b)) == a.partial_cmp(b)` for
503 /// all `a` and `b`. It's easy to accidentally make them disagree by
504 /// deriving some of the traits and manually implementing others.
506 /// Here's an example where you want to sort people by height only, disregarding `id`
510 /// use std::cmp::Ordering;
519 /// impl Ord for Person {
520 /// fn cmp(&self, other: &Self) -> Ordering {
521 /// self.height.cmp(&other.height)
525 /// impl PartialOrd for Person {
526 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
527 /// Some(self.cmp(other))
531 /// impl PartialEq for Person {
532 /// fn eq(&self, other: &Self) -> bool {
533 /// self.height == other.height
541 #[stable(feature = "rust1", since = "1.0.0")]
542 pub trait Ord: Eq + PartialOrd<Self> {
543 /// This method returns an `Ordering` between `self` and `other`.
545 /// By convention, `self.cmp(&other)` returns the ordering matching the expression
546 /// `self <operator> other` if true.
551 /// use std::cmp::Ordering;
553 /// assert_eq!(5.cmp(&10), Ordering::Less);
554 /// assert_eq!(10.cmp(&5), Ordering::Greater);
555 /// assert_eq!(5.cmp(&5), Ordering::Equal);
557 #[stable(feature = "rust1", since = "1.0.0")]
558 fn cmp(&self, other: &Self) -> Ordering;
560 /// Compares and returns the maximum of two values.
562 /// Returns the second argument if the comparison determines them to be equal.
567 /// assert_eq!(2, 1.max(2));
568 /// assert_eq!(2, 2.max(2));
570 #[stable(feature = "ord_max_min", since = "1.21.0")]
572 fn max(self, other: Self) -> Self
574 max_by(self, other, Ord::cmp)
577 /// Compares and returns the minimum of two values.
579 /// Returns the first argument if the comparison determines them to be equal.
584 /// assert_eq!(1, 1.min(2));
585 /// assert_eq!(2, 2.min(2));
587 #[stable(feature = "ord_max_min", since = "1.21.0")]
589 fn min(self, other: Self) -> Self
591 min_by(self, other, Ord::cmp)
594 /// Restrict a value to a certain interval.
596 /// Returns `max` if `self` is greater than `max`, and `min` if `self` is
597 /// less than `min`. Otherwise this returns `self`.
601 /// Panics if `min > max`.
606 /// #![feature(clamp)]
608 /// assert!((-3).clamp(-2, 1) == -2);
609 /// assert!(0.clamp(-2, 1) == 0);
610 /// assert!(2.clamp(-2, 1) == 1);
612 #[unstable(feature = "clamp", issue = "44095")]
613 fn clamp(self, min: Self, max: Self) -> Self
618 } else if self > max {
626 /// Derive macro generating an impl of the trait `Ord`.
627 #[rustc_builtin_macro]
628 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
629 #[allow_internal_unstable(core_intrinsics)]
630 pub macro Ord($item:item) { /* compiler built-in */ }
632 #[stable(feature = "rust1", since = "1.0.0")]
633 impl Eq for Ordering {}
635 #[stable(feature = "rust1", since = "1.0.0")]
636 impl Ord for Ordering {
638 fn cmp(&self, other: &Ordering) -> Ordering {
639 (*self as i32).cmp(&(*other as i32))
643 #[stable(feature = "rust1", since = "1.0.0")]
644 impl PartialOrd for Ordering {
646 fn partial_cmp(&self, other: &Ordering) -> Option<Ordering> {
647 (*self as i32).partial_cmp(&(*other as i32))
651 /// Trait for values that can be compared for a sort-order.
653 /// The comparison must satisfy, for all `a`, `b` and `c`:
655 /// - antisymmetry: if `a < b` then `!(a > b)`, as well as `a > b` implying `!(a < b)`; and
656 /// - transitivity: `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
658 /// Note that these requirements mean that the trait itself must be implemented symmetrically and
659 /// transitively: if `T: PartialOrd<U>` and `U: PartialOrd<V>` then `U: PartialOrd<T>` and `T:
664 /// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a
665 /// lexicographic ordering based on the top-to-bottom declaration order of the struct's members.
666 /// When `derive`d on enums, variants are ordered by their top-to-bottom declaration order.
668 /// ## How can I implement `PartialOrd`?
670 /// `PartialOrd` only requires implementation of the `partial_cmp` method, with the others
671 /// generated from default implementations.
673 /// However it remains possible to implement the others separately for types which do not have a
674 /// total order. For example, for floating point numbers, `NaN < 0 == false` and `NaN >= 0 ==
675 /// false` (cf. IEEE 754-2008 section 5.11).
677 /// `PartialOrd` requires your type to be `PartialEq`.
679 /// Implementations of `PartialEq`, `PartialOrd`, and `Ord` *must* agree with each other. It's
680 /// easy to accidentally make them disagree by deriving some of the traits and manually
681 /// implementing others.
683 /// If your type is `Ord`, you can implement `partial_cmp()` by using `cmp()`:
686 /// use std::cmp::Ordering;
695 /// impl PartialOrd for Person {
696 /// fn partial_cmp(&self, other: &Person) -> Option<Ordering> {
697 /// Some(self.cmp(other))
701 /// impl Ord for Person {
702 /// fn cmp(&self, other: &Person) -> Ordering {
703 /// self.height.cmp(&other.height)
707 /// impl PartialEq for Person {
708 /// fn eq(&self, other: &Person) -> bool {
709 /// self.height == other.height
714 /// You may also find it useful to use `partial_cmp()` on your type's fields. Here
715 /// is an example of `Person` types who have a floating-point `height` field that
716 /// is the only field to be used for sorting:
719 /// use std::cmp::Ordering;
727 /// impl PartialOrd for Person {
728 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
729 /// self.height.partial_cmp(&other.height)
733 /// impl PartialEq for Person {
734 /// fn eq(&self, other: &Self) -> bool {
735 /// self.height == other.height
746 /// assert_eq!(x < y, true);
747 /// assert_eq!(x.lt(&y), true);
749 #[lang = "partial_ord"]
750 #[stable(feature = "rust1", since = "1.0.0")]
755 #[rustc_on_unimplemented(
756 message="can't compare `{Self}` with `{Rhs}`",
757 label="no implementation for `{Self} < {Rhs}` and `{Self} > {Rhs}`",
759 pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
760 /// This method returns an ordering between `self` and `other` values if one exists.
765 /// use std::cmp::Ordering;
767 /// let result = 1.0.partial_cmp(&2.0);
768 /// assert_eq!(result, Some(Ordering::Less));
770 /// let result = 1.0.partial_cmp(&1.0);
771 /// assert_eq!(result, Some(Ordering::Equal));
773 /// let result = 2.0.partial_cmp(&1.0);
774 /// assert_eq!(result, Some(Ordering::Greater));
777 /// When comparison is impossible:
780 /// let result = std::f64::NAN.partial_cmp(&1.0);
781 /// assert_eq!(result, None);
784 #[stable(feature = "rust1", since = "1.0.0")]
785 fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>;
787 /// This method tests less than (for `self` and `other`) and is used by the `<` operator.
792 /// let result = 1.0 < 2.0;
793 /// assert_eq!(result, true);
795 /// let result = 2.0 < 1.0;
796 /// assert_eq!(result, false);
800 #[stable(feature = "rust1", since = "1.0.0")]
801 fn lt(&self, other: &Rhs) -> bool {
802 match self.partial_cmp(other) {
808 /// This method tests less than or equal to (for `self` and `other`) and is used by the `<=`
814 /// let result = 1.0 <= 2.0;
815 /// assert_eq!(result, true);
817 /// let result = 2.0 <= 2.0;
818 /// assert_eq!(result, true);
822 #[stable(feature = "rust1", since = "1.0.0")]
823 fn le(&self, other: &Rhs) -> bool {
824 match self.partial_cmp(other) {
825 Some(Less) | Some(Equal) => true,
830 /// This method tests greater than (for `self` and `other`) and is used by the `>` operator.
835 /// let result = 1.0 > 2.0;
836 /// assert_eq!(result, false);
838 /// let result = 2.0 > 2.0;
839 /// assert_eq!(result, false);
843 #[stable(feature = "rust1", since = "1.0.0")]
844 fn gt(&self, other: &Rhs) -> bool {
845 match self.partial_cmp(other) {
846 Some(Greater) => true,
851 /// This method tests greater than or equal to (for `self` and `other`) and is used by the `>=`
857 /// let result = 2.0 >= 1.0;
858 /// assert_eq!(result, true);
860 /// let result = 2.0 >= 2.0;
861 /// assert_eq!(result, true);
865 #[stable(feature = "rust1", since = "1.0.0")]
866 fn ge(&self, other: &Rhs) -> bool {
867 match self.partial_cmp(other) {
868 Some(Greater) | Some(Equal) => true,
874 /// Derive macro generating an impl of the trait `PartialOrd`.
875 #[rustc_builtin_macro]
876 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
877 #[allow_internal_unstable(core_intrinsics)]
878 pub macro PartialOrd($item:item) { /* compiler built-in */ }
880 /// Compares and returns the minimum of two values.
882 /// Returns the first argument if the comparison determines them to be equal.
884 /// Internally uses an alias to `Ord::min`.
891 /// assert_eq!(1, cmp::min(1, 2));
892 /// assert_eq!(2, cmp::min(2, 2));
895 #[stable(feature = "rust1", since = "1.0.0")]
896 pub fn min<T: Ord>(v1: T, v2: T) -> T {
900 /// Returns the minimum of two values with respect to the specified comparison function.
902 /// Returns the first argument if the comparison determines them to be equal.
907 /// #![feature(cmp_min_max_by)]
911 /// assert_eq!(cmp::min_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), 1);
912 /// assert_eq!(cmp::min_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), -2);
915 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
916 pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
917 match compare(&v1, &v2) {
918 Ordering::Less | Ordering::Equal => v1,
919 Ordering::Greater => v2,
923 /// Returns the element that gives the minimum value from the specified 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_key(-2, 1, |x: &i32| x.abs()), 1);
935 /// assert_eq!(cmp::min_by_key(-2, 2, |x: &i32| x.abs()), -2);
938 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
939 pub fn min_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
940 min_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
943 /// Compares and returns the maximum of two values.
945 /// Returns the second argument if the comparison determines them to be equal.
947 /// Internally uses an alias to `Ord::max`.
954 /// assert_eq!(2, cmp::max(1, 2));
955 /// assert_eq!(2, cmp::max(2, 2));
958 #[stable(feature = "rust1", since = "1.0.0")]
959 pub fn max<T: Ord>(v1: T, v2: T) -> T {
963 /// Returns the maximum of two values with respect to the specified comparison function.
965 /// Returns the second argument if the comparison determines them to be equal.
970 /// #![feature(cmp_min_max_by)]
974 /// assert_eq!(cmp::max_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), -2);
975 /// assert_eq!(cmp::max_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), 2);
978 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
979 pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
980 match compare(&v1, &v2) {
981 Ordering::Less | Ordering::Equal => v2,
982 Ordering::Greater => v1,
986 /// Returns the element that gives the maximum value from the specified 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_key(-2, 1, |x: &i32| x.abs()), -2);
998 /// assert_eq!(cmp::max_by_key(-2, 2, |x: &i32| x.abs()), 2);
1001 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
1002 pub fn max_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
1003 max_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
1006 // Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types
1008 use crate::hint::unreachable_unchecked;
1009 use crate::cmp::Ordering::{self, Less, Greater, Equal};
1011 macro_rules! partial_eq_impl {
1013 #[stable(feature = "rust1", since = "1.0.0")]
1014 impl PartialEq for $t {
1016 fn eq(&self, other: &$t) -> bool { (*self) == (*other) }
1018 fn ne(&self, other: &$t) -> bool { (*self) != (*other) }
1023 #[stable(feature = "rust1", since = "1.0.0")]
1024 impl PartialEq for () {
1026 fn eq(&self, _other: &()) -> bool { true }
1028 fn ne(&self, _other: &()) -> bool { false }
1032 bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64
1035 macro_rules! eq_impl {
1037 #[stable(feature = "rust1", since = "1.0.0")]
1042 eq_impl! { () bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
1044 macro_rules! partial_ord_impl {
1046 #[stable(feature = "rust1", since = "1.0.0")]
1047 impl PartialOrd for $t {
1049 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
1050 match (self <= other, self >= other) {
1051 (false, false) => None,
1052 (false, true) => Some(Greater),
1053 (true, false) => Some(Less),
1054 (true, true) => Some(Equal),
1058 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
1060 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
1062 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
1064 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
1069 #[stable(feature = "rust1", since = "1.0.0")]
1070 impl PartialOrd for () {
1072 fn partial_cmp(&self, _: &()) -> Option<Ordering> {
1077 #[stable(feature = "rust1", since = "1.0.0")]
1078 impl PartialOrd for bool {
1080 fn partial_cmp(&self, other: &bool) -> Option<Ordering> {
1081 (*self as u8).partial_cmp(&(*other as u8))
1085 partial_ord_impl! { f32 f64 }
1087 macro_rules! ord_impl {
1089 #[stable(feature = "rust1", since = "1.0.0")]
1090 impl PartialOrd for $t {
1092 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
1093 Some(self.cmp(other))
1096 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
1098 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
1100 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
1102 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
1105 #[stable(feature = "rust1", since = "1.0.0")]
1108 fn cmp(&self, other: &$t) -> Ordering {
1109 // The order here is important to generate more optimal assembly.
1110 // See <https://github.com/rust-lang/rust/issues/63758> for more info.
1111 if *self < *other { Less }
1112 else if *self == *other { Equal }
1119 #[stable(feature = "rust1", since = "1.0.0")]
1122 fn cmp(&self, _other: &()) -> Ordering { Equal }
1125 #[stable(feature = "rust1", since = "1.0.0")]
1128 fn cmp(&self, other: &bool) -> Ordering {
1129 // Casting to i8's and converting the difference to an Ordering generates
1130 // more optimal assembly.
1131 // See <https://github.com/rust-lang/rust/issues/66780> for more info.
1132 match (*self as i8) - (*other as i8) {
1136 // SAFETY: bool as i8 returns 0 or 1, so the difference can't be anything else
1137 _ => unsafe { unreachable_unchecked() },
1142 ord_impl! { char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
1144 #[unstable(feature = "never_type", issue = "35121")]
1145 impl PartialEq for ! {
1146 fn eq(&self, _: &!) -> bool {
1151 #[unstable(feature = "never_type", issue = "35121")]
1154 #[unstable(feature = "never_type", issue = "35121")]
1155 impl PartialOrd for ! {
1156 fn partial_cmp(&self, _: &!) -> Option<Ordering> {
1161 #[unstable(feature = "never_type", issue = "35121")]
1163 fn cmp(&self, _: &!) -> Ordering {
1170 #[stable(feature = "rust1", since = "1.0.0")]
1171 impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &A where A: PartialEq<B> {
1173 fn eq(&self, other: & &B) -> bool { PartialEq::eq(*self, *other) }
1175 fn ne(&self, other: & &B) -> bool { PartialEq::ne(*self, *other) }
1177 #[stable(feature = "rust1", since = "1.0.0")]
1178 impl<A: ?Sized, B: ?Sized> PartialOrd<&B> for &A where A: PartialOrd<B> {
1180 fn partial_cmp(&self, other: &&B) -> Option<Ordering> {
1181 PartialOrd::partial_cmp(*self, *other)
1184 fn lt(&self, other: & &B) -> bool { PartialOrd::lt(*self, *other) }
1186 fn le(&self, other: & &B) -> bool { PartialOrd::le(*self, *other) }
1188 fn gt(&self, other: & &B) -> bool { PartialOrd::gt(*self, *other) }
1190 fn ge(&self, other: & &B) -> bool { PartialOrd::ge(*self, *other) }
1192 #[stable(feature = "rust1", since = "1.0.0")]
1193 impl<A: ?Sized> Ord for &A where A: Ord {
1195 fn cmp(&self, other: &Self) -> Ordering { Ord::cmp(*self, *other) }
1197 #[stable(feature = "rust1", since = "1.0.0")]
1198 impl<A: ?Sized> Eq for &A where A: Eq {}
1202 #[stable(feature = "rust1", since = "1.0.0")]
1203 impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &mut A where A: PartialEq<B> {
1205 fn eq(&self, other: &&mut B) -> bool { PartialEq::eq(*self, *other) }
1207 fn ne(&self, other: &&mut B) -> bool { PartialEq::ne(*self, *other) }
1209 #[stable(feature = "rust1", since = "1.0.0")]
1210 impl<A: ?Sized, B: ?Sized> PartialOrd<&mut B> for &mut A where A: PartialOrd<B> {
1212 fn partial_cmp(&self, other: &&mut B) -> Option<Ordering> {
1213 PartialOrd::partial_cmp(*self, *other)
1216 fn lt(&self, other: &&mut B) -> bool { PartialOrd::lt(*self, *other) }
1218 fn le(&self, other: &&mut B) -> bool { PartialOrd::le(*self, *other) }
1220 fn gt(&self, other: &&mut B) -> bool { PartialOrd::gt(*self, *other) }
1222 fn ge(&self, other: &&mut B) -> bool { PartialOrd::ge(*self, *other) }
1224 #[stable(feature = "rust1", since = "1.0.0")]
1225 impl<A: ?Sized> Ord for &mut A where A: Ord {
1227 fn cmp(&self, other: &Self) -> Ordering { Ord::cmp(*self, *other) }
1229 #[stable(feature = "rust1", since = "1.0.0")]
1230 impl<A: ?Sized> Eq for &mut A where A: Eq {}
1232 #[stable(feature = "rust1", since = "1.0.0")]
1233 impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &A where A: PartialEq<B> {
1235 fn eq(&self, other: &&mut B) -> bool { PartialEq::eq(*self, *other) }
1237 fn ne(&self, other: &&mut B) -> bool { PartialEq::ne(*self, *other) }
1240 #[stable(feature = "rust1", since = "1.0.0")]
1241 impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &mut A where A: PartialEq<B> {
1243 fn eq(&self, other: &&B) -> bool { PartialEq::eq(*self, *other) }
1245 fn ne(&self, other: &&B) -> bool { PartialEq::ne(*self, *other) }