1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Functionality for ordering and comparison.
13 //! This module defines both `PartialOrd` and `PartialEq` traits which are used
14 //! by the compiler to implement comparison operators. Rust programs may
15 //! implement `PartialOrd` to overload the `<`, `<=`, `>`, and `>=` operators,
16 //! and may implement `PartialEq` to overload the `==` and `!=` operators.
24 //! // these two lines are equivalent
25 //! assert_eq!(x < y, true);
26 //! assert_eq!(x.lt(&y), true);
28 //! // these two lines are also equivalent
29 //! assert_eq!(x == y, false);
30 //! assert_eq!(x.eq(&y), false);
33 #![stable(feature = "rust1", since = "1.0.0")]
35 use self::Ordering::*;
38 use option::Option::{self, Some};
40 /// Trait for equality comparisons which are [partial equivalence
41 /// relations](http://en.wikipedia.org/wiki/Partial_equivalence_relation).
43 /// This trait allows for partial equality, for types that do not have a full
44 /// equivalence relation. For example, in floating point numbers `NaN != NaN`,
45 /// so floating point types implement `PartialEq` but not `Eq`.
47 /// Formally, the equality must be (for all `a`, `b` and `c`):
49 /// - symmetric: `a == b` implies `b == a`; and
50 /// - transitive: `a == b` and `b == c` implies `a == c`.
52 /// Note that these requirements mean that the trait itself must be implemented
53 /// symmetrically and transitively: if `T: PartialEq<U>` and `U: PartialEq<V>`
54 /// then `U: PartialEq<T>` and `T: PartialEq<V>`.
58 /// This trait can be used with `#[derive]`. When `derive`d on structs, two
59 /// instances are equal if all fields are equal, and not equal if any fields
60 /// are not equal. When `derive`d on enums, each variant is equal to itself
61 /// and not equal to the other variants.
63 /// ## How can I implement `PartialEq`?
65 /// PartialEq only requires the `eq` method to be implemented; `ne` is defined
66 /// in terms of it by default. Any manual implementation of `ne` *must* respect
67 /// the rule that `eq` is a strict inverse of `ne`; that is, `!(a == b)` if and
70 /// An example implementation for a domain in which two books are considered
71 /// the same book if their ISBN matches, even if the formats differ:
74 /// enum BookFormat { Paperback, Hardback, Ebook }
77 /// format: BookFormat,
80 /// impl PartialEq for Book {
81 /// fn eq(&self, other: &Self) -> bool {
82 /// self.isbn == other.isbn
86 /// let b1 = Book { isbn: 3, format: BookFormat::Paperback };
87 /// let b2 = Book { isbn: 3, format: BookFormat::Ebook };
88 /// let b3 = Book { isbn: 10, format: BookFormat::Paperback };
90 /// assert!(b1 == b2);
91 /// assert!(b1 != b3);
100 /// assert_eq!(x == y, false);
101 /// assert_eq!(x.eq(&y), false);
104 #[stable(feature = "rust1", since = "1.0.0")]
105 pub trait PartialEq<Rhs: ?Sized = Self> {
106 /// This method tests for `self` and `other` values to be equal, and is used
108 #[stable(feature = "rust1", since = "1.0.0")]
109 fn eq(&self, other: &Rhs) -> bool;
111 /// This method tests for `!=`.
113 #[stable(feature = "rust1", since = "1.0.0")]
114 fn ne(&self, other: &Rhs) -> bool { !self.eq(other) }
117 /// Trait for equality comparisons which are [equivalence relations](
118 /// https://en.wikipedia.org/wiki/Equivalence_relation).
120 /// This means, that in addition to `a == b` and `a != b` being strict inverses, the equality must
121 /// be (for all `a`, `b` and `c`):
123 /// - reflexive: `a == a`;
124 /// - symmetric: `a == b` implies `b == a`; and
125 /// - transitive: `a == b` and `b == c` implies `a == c`.
127 /// This property cannot be checked by the compiler, and therefore `Eq` implies
128 /// `PartialEq`, and has no extra methods.
132 /// This trait can be used with `#[derive]`. When `derive`d, because `Eq` has
133 /// no extra methods, it is only informing the compiler that this is an
134 /// equivalence relation rather than a partial equivalence relation. Note that
135 /// the `derive` strategy requires all fields are `PartialEq`, which isn't
138 /// ## How can I implement `Eq`?
140 /// If you cannot use the `derive` strategy, specify that your type implements
141 /// `Eq`, which has no methods:
144 /// enum BookFormat { Paperback, Hardback, Ebook }
147 /// format: BookFormat,
149 /// impl PartialEq for Book {
150 /// fn eq(&self, other: &Self) -> bool {
151 /// self.isbn == other.isbn
154 /// impl Eq for Book {}
156 #[stable(feature = "rust1", since = "1.0.0")]
157 pub trait Eq: PartialEq<Self> {
158 // FIXME #13101: this method is used solely by #[deriving] to
159 // assert that every component of a type implements #[deriving]
160 // itself, the current deriving infrastructure means doing this
161 // assertion without using a method on this trait is nearly
164 // This should never be implemented by hand.
167 #[stable(feature = "rust1", since = "1.0.0")]
168 fn assert_receiver_is_total_eq(&self) {}
171 /// An `Ordering` is the result of a comparison between two values.
176 /// use std::cmp::Ordering;
178 /// let result = 1.cmp(&2);
179 /// assert_eq!(Ordering::Less, result);
181 /// let result = 1.cmp(&1);
182 /// assert_eq!(Ordering::Equal, result);
184 /// let result = 2.cmp(&1);
185 /// assert_eq!(Ordering::Greater, result);
187 #[derive(Clone, Copy, PartialEq, Debug, Hash)]
188 #[stable(feature = "rust1", since = "1.0.0")]
190 /// An ordering where a compared value is less [than another].
191 #[stable(feature = "rust1", since = "1.0.0")]
193 /// An ordering where a compared value is equal [to another].
194 #[stable(feature = "rust1", since = "1.0.0")]
196 /// An ordering where a compared value is greater [than another].
197 #[stable(feature = "rust1", since = "1.0.0")]
202 /// Reverse the `Ordering`.
204 /// * `Less` becomes `Greater`.
205 /// * `Greater` becomes `Less`.
206 /// * `Equal` becomes `Equal`.
213 /// use std::cmp::Ordering;
215 /// assert_eq!(Ordering::Less.reverse(), Ordering::Greater);
216 /// assert_eq!(Ordering::Equal.reverse(), Ordering::Equal);
217 /// assert_eq!(Ordering::Greater.reverse(), Ordering::Less);
220 /// This method can be used to reverse a comparison:
223 /// let mut data: &mut [_] = &mut [2, 10, 5, 8];
225 /// // sort the array from largest to smallest.
226 /// data.sort_by(|a, b| a.cmp(b).reverse());
228 /// let b: &mut [_] = &mut [10, 8, 5, 2];
229 /// assert!(data == b);
232 #[stable(feature = "rust1", since = "1.0.0")]
233 pub fn reverse(self) -> Ordering {
242 /// Trait for types that form a [total order](https://en.wikipedia.org/wiki/Total_order).
244 /// An order is a total order if it is (for all `a`, `b` and `c`):
246 /// - total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true; and
247 /// - transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
251 /// This trait can be used with `#[derive]`. When `derive`d, it will produce a lexicographic
252 /// ordering based on the top-to-bottom declaration order of the struct's members.
254 /// ## How can I implement `Ord`?
256 /// `Ord` requires that the type also be `PartialOrd` and `Eq` (which requires `PartialEq`).
258 /// Then you must define an implementation for `cmp()`. You may find it useful to use
259 /// `cmp()` on your type's fields.
261 /// Here's an example where you want to sort people by height only, disregarding `id`
265 /// use std::cmp::Ordering;
274 /// impl Ord for Person {
275 /// fn cmp(&self, other: &Self) -> Ordering {
276 /// self.height.cmp(&other.height)
280 /// impl PartialOrd for Person {
281 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
282 /// Some(self.cmp(other))
286 /// impl PartialEq for Person {
287 /// fn eq(&self, other: &Self) -> bool {
288 /// self.height == other.height
292 #[stable(feature = "rust1", since = "1.0.0")]
293 pub trait Ord: Eq + PartialOrd<Self> {
294 /// This method returns an `Ordering` between `self` and `other`.
296 /// By convention, `self.cmp(&other)` returns the ordering matching the expression
297 /// `self <operator> other` if true.
302 /// use std::cmp::Ordering;
304 /// assert_eq!(5.cmp(&10), Ordering::Less);
305 /// assert_eq!(10.cmp(&5), Ordering::Greater);
306 /// assert_eq!(5.cmp(&5), Ordering::Equal);
308 #[stable(feature = "rust1", since = "1.0.0")]
309 fn cmp(&self, other: &Self) -> Ordering;
312 #[stable(feature = "rust1", since = "1.0.0")]
313 impl Eq for Ordering {}
315 #[stable(feature = "rust1", since = "1.0.0")]
316 impl Ord for Ordering {
318 fn cmp(&self, other: &Ordering) -> Ordering {
319 (*self as i32).cmp(&(*other as i32))
323 #[stable(feature = "rust1", since = "1.0.0")]
324 impl PartialOrd for Ordering {
326 fn partial_cmp(&self, other: &Ordering) -> Option<Ordering> {
327 (*self as i32).partial_cmp(&(*other as i32))
331 /// Trait for values that can be compared for a sort-order.
333 /// The comparison must satisfy, for all `a`, `b` and `c`:
335 /// - antisymmetry: if `a < b` then `!(a > b)`, as well as `a > b` implying `!(a < b)`; and
336 /// - transitivity: `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
338 /// Note that these requirements mean that the trait itself must be implemented symmetrically and
339 /// transitively: if `T: PartialOrd<U>` and `U: PartialOrd<V>` then `U: PartialOrd<T>` and `T:
344 /// This trait can be used with `#[derive]`. When `derive`d, it will produce a lexicographic
345 /// ordering based on the top-to-bottom declaration order of the struct's members.
347 /// ## How can I implement `Ord`?
349 /// PartialOrd only requires implementation of the `partial_cmp` method, with the others generated
350 /// from default implementations.
352 /// However it remains possible to implement the others separately for types which do not have a
353 /// total order. For example, for floating point numbers, `NaN < 0 == false` and `NaN >= 0 ==
354 /// false` (cf. IEEE 754-2008 section 5.11).
356 /// `PartialOrd` requires your type to be `PartialEq`.
358 /// If your type is `Ord`, you can implement `partial_cmp()` by using `cmp()`:
361 /// impl PartialOrd for Person {
362 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
363 /// Some(self.cmp(other))
368 /// You may also find it useful to use `partial_cmp()` on your type`s fields. Here
369 /// is an example of `Person` types who have a floating-point `height` field that
370 /// is the only field to be used for sorting:
373 /// use std::cmp::Ordering;
381 /// impl PartialOrd for Person {
382 /// fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
383 /// self.height.partial_cmp(&other.height)
387 /// impl PartialEq for Person {
388 /// fn eq(&self, other: &Self) -> bool {
389 /// self.height == other.height
400 /// assert_eq!(x < y, true);
401 /// assert_eq!(x.lt(&y), true);
404 #[stable(feature = "rust1", since = "1.0.0")]
405 pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
406 /// This method returns an ordering between `self` and `other` values if one exists.
411 /// use std::cmp::Ordering;
413 /// let result = 1.0.partial_cmp(&2.0);
414 /// assert_eq!(result, Some(Ordering::Less));
416 /// let result = 1.0.partial_cmp(&1.0);
417 /// assert_eq!(result, Some(Ordering::Equal));
419 /// let result = 2.0.partial_cmp(&1.0);
420 /// assert_eq!(result, Some(Ordering::Greater));
423 /// When comparison is impossible:
426 /// let result = std::f64::NAN.partial_cmp(&1.0);
427 /// assert_eq!(result, None);
429 #[stable(feature = "rust1", since = "1.0.0")]
430 fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>;
432 /// This method tests less than (for `self` and `other`) and is used by the `<` operator.
437 /// let result = 1.0 < 2.0;
438 /// assert_eq!(result, true);
440 /// let result = 2.0 < 1.0;
441 /// assert_eq!(result, false);
444 #[stable(feature = "rust1", since = "1.0.0")]
445 fn lt(&self, other: &Rhs) -> bool {
446 match self.partial_cmp(other) {
452 /// This method tests less than or equal to (for `self` and `other`) and is used by the `<=`
458 /// let result = 1.0 <= 2.0;
459 /// assert_eq!(result, true);
461 /// let result = 2.0 <= 2.0;
462 /// assert_eq!(result, true);
465 #[stable(feature = "rust1", since = "1.0.0")]
466 fn le(&self, other: &Rhs) -> bool {
467 match self.partial_cmp(other) {
468 Some(Less) | Some(Equal) => true,
473 /// This method tests greater than (for `self` and `other`) and is used by the `>` operator.
478 /// let result = 1.0 > 2.0;
479 /// assert_eq!(result, false);
481 /// let result = 2.0 > 2.0;
482 /// assert_eq!(result, false);
485 #[stable(feature = "rust1", since = "1.0.0")]
486 fn gt(&self, other: &Rhs) -> bool {
487 match self.partial_cmp(other) {
488 Some(Greater) => true,
493 /// This method tests greater than or equal to (for `self` and `other`) and is used by the `>=`
499 /// let result = 2.0 >= 1.0;
500 /// assert_eq!(result, true);
502 /// let result = 2.0 >= 2.0;
503 /// assert_eq!(result, true);
506 #[stable(feature = "rust1", since = "1.0.0")]
507 fn ge(&self, other: &Rhs) -> bool {
508 match self.partial_cmp(other) {
509 Some(Greater) | Some(Equal) => true,
515 /// Compare and return the minimum of two values.
517 /// Returns the first argument if the comparison determines them to be equal.
524 /// assert_eq!(1, cmp::min(1, 2));
525 /// assert_eq!(2, cmp::min(2, 2));
528 #[stable(feature = "rust1", since = "1.0.0")]
529 pub fn min<T: Ord>(v1: T, v2: T) -> T {
530 if v1 <= v2 { v1 } else { v2 }
533 /// Compare and return the maximum of two values.
535 /// Returns the second argument if the comparison determines them to be equal.
542 /// assert_eq!(2, cmp::max(1, 2));
543 /// assert_eq!(2, cmp::max(2, 2));
546 #[stable(feature = "rust1", since = "1.0.0")]
547 pub fn max<T: Ord>(v1: T, v2: T) -> T {
548 if v2 >= v1 { v2 } else { v1 }
551 // Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types
553 use cmp::{PartialOrd, Ord, PartialEq, Eq, Ordering};
554 use cmp::Ordering::{Less, Greater, Equal};
557 use option::Option::{Some, None};
559 macro_rules! partial_eq_impl {
561 #[stable(feature = "rust1", since = "1.0.0")]
562 impl PartialEq for $t {
564 fn eq(&self, other: &$t) -> bool { (*self) == (*other) }
566 fn ne(&self, other: &$t) -> bool { (*self) != (*other) }
571 #[stable(feature = "rust1", since = "1.0.0")]
572 impl PartialEq for () {
574 fn eq(&self, _other: &()) -> bool { true }
576 fn ne(&self, _other: &()) -> bool { false }
580 bool char usize u8 u16 u32 u64 isize i8 i16 i32 i64 f32 f64
583 macro_rules! eq_impl {
585 #[stable(feature = "rust1", since = "1.0.0")]
590 eq_impl! { () bool char usize u8 u16 u32 u64 isize i8 i16 i32 i64 }
592 macro_rules! partial_ord_impl {
594 #[stable(feature = "rust1", since = "1.0.0")]
595 impl PartialOrd for $t {
597 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
598 match (self <= other, self >= other) {
599 (false, false) => None,
600 (false, true) => Some(Greater),
601 (true, false) => Some(Less),
602 (true, true) => Some(Equal),
606 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
608 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
610 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
612 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
617 #[stable(feature = "rust1", since = "1.0.0")]
618 impl PartialOrd for () {
620 fn partial_cmp(&self, _: &()) -> Option<Ordering> {
625 #[stable(feature = "rust1", since = "1.0.0")]
626 impl PartialOrd for bool {
628 fn partial_cmp(&self, other: &bool) -> Option<Ordering> {
629 (*self as u8).partial_cmp(&(*other as u8))
633 partial_ord_impl! { f32 f64 }
635 macro_rules! ord_impl {
637 #[stable(feature = "rust1", since = "1.0.0")]
638 impl PartialOrd for $t {
640 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
641 Some(self.cmp(other))
644 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
646 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
648 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
650 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
653 #[stable(feature = "rust1", since = "1.0.0")]
656 fn cmp(&self, other: &$t) -> Ordering {
657 if *self == *other { Equal }
658 else if *self < *other { Less }
665 #[stable(feature = "rust1", since = "1.0.0")]
668 fn cmp(&self, _other: &()) -> Ordering { Equal }
671 #[stable(feature = "rust1", since = "1.0.0")]
674 fn cmp(&self, other: &bool) -> Ordering {
675 (*self as u8).cmp(&(*other as u8))
679 ord_impl! { char usize u8 u16 u32 u64 isize i8 i16 i32 i64 }
683 #[stable(feature = "rust1", since = "1.0.0")]
684 impl<'a, 'b, A: ?Sized, B: ?Sized> PartialEq<&'b B> for &'a A where A: PartialEq<B> {
686 fn eq(&self, other: & &'b B) -> bool { PartialEq::eq(*self, *other) }
688 fn ne(&self, other: & &'b B) -> bool { PartialEq::ne(*self, *other) }
690 #[stable(feature = "rust1", since = "1.0.0")]
691 impl<'a, 'b, A: ?Sized, B: ?Sized> PartialOrd<&'b B> for &'a A where A: PartialOrd<B> {
693 fn partial_cmp(&self, other: &&'b B) -> Option<Ordering> {
694 PartialOrd::partial_cmp(*self, *other)
697 fn lt(&self, other: & &'b B) -> bool { PartialOrd::lt(*self, *other) }
699 fn le(&self, other: & &'b B) -> bool { PartialOrd::le(*self, *other) }
701 fn ge(&self, other: & &'b B) -> bool { PartialOrd::ge(*self, *other) }
703 fn gt(&self, other: & &'b B) -> bool { PartialOrd::gt(*self, *other) }
705 #[stable(feature = "rust1", since = "1.0.0")]
706 impl<'a, A: ?Sized> Ord for &'a A where A: Ord {
708 fn cmp(&self, other: & &'a A) -> Ordering { Ord::cmp(*self, *other) }
710 #[stable(feature = "rust1", since = "1.0.0")]
711 impl<'a, A: ?Sized> Eq for &'a A where A: Eq {}
715 #[stable(feature = "rust1", since = "1.0.0")]
716 impl<'a, 'b, A: ?Sized, B: ?Sized> PartialEq<&'b mut B> for &'a mut A where A: PartialEq<B> {
718 fn eq(&self, other: &&'b mut B) -> bool { PartialEq::eq(*self, *other) }
720 fn ne(&self, other: &&'b mut B) -> bool { PartialEq::ne(*self, *other) }
722 #[stable(feature = "rust1", since = "1.0.0")]
723 impl<'a, 'b, A: ?Sized, B: ?Sized> PartialOrd<&'b mut B> for &'a mut A where A: PartialOrd<B> {
725 fn partial_cmp(&self, other: &&'b mut B) -> Option<Ordering> {
726 PartialOrd::partial_cmp(*self, *other)
729 fn lt(&self, other: &&'b mut B) -> bool { PartialOrd::lt(*self, *other) }
731 fn le(&self, other: &&'b mut B) -> bool { PartialOrd::le(*self, *other) }
733 fn ge(&self, other: &&'b mut B) -> bool { PartialOrd::ge(*self, *other) }
735 fn gt(&self, other: &&'b mut B) -> bool { PartialOrd::gt(*self, *other) }
737 #[stable(feature = "rust1", since = "1.0.0")]
738 impl<'a, A: ?Sized> Ord for &'a mut A where A: Ord {
740 fn cmp(&self, other: &&'a mut A) -> Ordering { Ord::cmp(*self, *other) }
742 #[stable(feature = "rust1", since = "1.0.0")]
743 impl<'a, A: ?Sized> Eq for &'a mut A where A: Eq {}
745 #[stable(feature = "rust1", since = "1.0.0")]
746 impl<'a, 'b, A: ?Sized, B: ?Sized> PartialEq<&'b mut B> for &'a A where A: PartialEq<B> {
748 fn eq(&self, other: &&'b mut B) -> bool { PartialEq::eq(*self, *other) }
750 fn ne(&self, other: &&'b mut B) -> bool { PartialEq::ne(*self, *other) }
753 #[stable(feature = "rust1", since = "1.0.0")]
754 impl<'a, 'b, A: ?Sized, B: ?Sized> PartialEq<&'b B> for &'a mut A where A: PartialEq<B> {
756 fn eq(&self, other: &&'b B) -> bool { PartialEq::eq(*self, *other) }
758 fn ne(&self, other: &&'b B) -> bool { PartialEq::ne(*self, *other) }