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 //! Defines the `PartialOrd` and `PartialEq` comparison traits.
13 //! This module defines both `PartialOrd` and `PartialEq` traits which are used by the
14 //! compiler to implement comparison operators. Rust programs may implement
15 //!`PartialOrd` to overload the `<`, `<=`, `>`, and `>=` operators, and may implement
16 //! `PartialEq` to overload the `==` and `!=` operators.
18 //! For example, to define a type with a customized definition for the PartialEq
19 //! operators, you could do the following:
22 //! use core::num::SignedInt;
25 //! struct SketchyNum {
29 //! // Our implementation of `PartialEq` to support `==` and `!=`.
30 //! impl PartialEq for SketchyNum {
31 //! // Our custom eq allows numbers which are near each other to be equal! :D
32 //! fn eq(&self, other: &SketchyNum) -> bool {
33 //! (self.num - other.num).abs() < 5
37 //! // Now these binary operators will work when applied!
38 //! assert!(SketchyNum {num: 37} == SketchyNum {num: 34});
39 //! assert!(SketchyNum {num: 25} != SketchyNum {num: 57});
44 use self::Ordering::*;
47 use option::Option::{self, Some, None};
49 /// Trait for equality comparisons which are [partial equivalence relations](
50 /// http://en.wikipedia.org/wiki/Partial_equivalence_relation).
52 /// This trait allows for partial equality, for types that do not have a full
53 /// equivalence relation. For example, in floating point numbers `NaN != NaN`,
54 /// so floating point types implement `PartialEq` but not `Eq`.
56 /// Formally, the equality must be (for all `a`, `b` and `c`):
58 /// - symmetric: `a == b` implies `b == a`; and
59 /// - transitive: `a == b` and `b == c` implies `a == c`.
61 /// Note that these requirements mean that the trait itself must be
62 /// implemented symmetrically and transitively: if `T: PartialEq<U>`
63 /// and `U: PartialEq<V>` then `U: PartialEq<T>` and `T:
66 /// PartialEq only requires the `eq` method to be implemented; `ne` is defined
67 /// in terms of it by default. Any manual implementation of `ne` *must* respect
68 /// the rule that `eq` is a strict inverse of `ne`; that is, `!(a == b)` if and
73 pub trait PartialEq<Sized? Rhs = Self> for Sized? {
74 /// This method tests for `self` and `other` values to be equal, and is used by `==`.
76 fn eq(&self, other: &Rhs) -> bool;
78 /// This method tests for `!=`.
81 fn ne(&self, other: &Rhs) -> bool { !self.eq(other) }
84 /// Trait for equality comparisons which are [equivalence relations](
85 /// https://en.wikipedia.org/wiki/Equivalence_relation).
87 /// This means, that in addition to `a == b` and `a != b` being strict
88 /// inverses, the equality must be (for all `a`, `b` and `c`):
90 /// - reflexive: `a == a`;
91 /// - symmetric: `a == b` implies `b == a`; and
92 /// - transitive: `a == b` and `b == c` implies `a == c`.
94 pub trait Eq for Sized?: PartialEq<Self> {
95 // FIXME #13101: this method is used solely by #[deriving] to
96 // assert that every component of a type implements #[deriving]
97 // itself, the current deriving infrastructure means doing this
98 // assertion without using a method on this trait is nearly
101 // This should never be implemented by hand.
104 fn assert_receiver_is_total_eq(&self) {}
107 /// An ordering is, e.g, a result of a comparison between two values.
108 #[derive(Clone, Copy, PartialEq, Show)]
111 /// An ordering where a compared value is less [than another].
114 /// An ordering where a compared value is equal [to another].
117 /// An ordering where a compared value is greater [than another].
123 /// Reverse the `Ordering`, so that `Less` becomes `Greater` and
129 /// use std::cmp::Ordering::{Less, Equal, Greater};
131 /// assert_eq!(Less.reverse(), Greater);
132 /// assert_eq!(Equal.reverse(), Equal);
133 /// assert_eq!(Greater.reverse(), Less);
135 /// let mut data: &mut [_] = &mut [2u, 10, 5, 8];
137 /// // sort the array from largest to smallest.
138 /// data.sort_by(|a, b| a.cmp(b).reverse());
140 /// let b: &mut [_] = &mut [10u, 8, 5, 2];
141 /// assert!(data == b);
145 pub fn reverse(self) -> Ordering {
147 // this compiles really nicely (to a single instruction);
148 // an explicit match has a pile of branches and
151 // NB. it is safe because of the explicit discriminants
153 ::mem::transmute::<_, Ordering>(-(self as i8))
158 /// Trait for types that form a [total order](
159 /// https://en.wikipedia.org/wiki/Total_order).
161 /// An order is a total order if it is (for all `a`, `b` and `c`):
163 /// - total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is
165 /// - transitive, `a < b` and `b < c` implies `a < c`. The same must hold for
166 /// both `==` and `>`.
168 pub trait Ord for Sized?: Eq + PartialOrd<Self> {
169 /// This method returns an ordering between `self` and `other` values.
171 /// By convention, `self.cmp(&other)` returns the ordering matching
172 /// the expression `self <operator> other` if true. For example:
175 /// use std::cmp::Ordering::{Less, Equal, Greater};
177 /// assert_eq!( 5u.cmp(&10), Less); // because 5 < 10
178 /// assert_eq!(10u.cmp(&5), Greater); // because 10 > 5
179 /// assert_eq!( 5u.cmp(&5), Equal); // because 5 == 5
182 fn cmp(&self, other: &Self) -> Ordering;
186 impl Eq for Ordering {}
189 impl Ord for Ordering {
192 fn cmp(&self, other: &Ordering) -> Ordering {
193 (*self as int).cmp(&(*other as int))
198 impl PartialOrd for Ordering {
201 fn partial_cmp(&self, other: &Ordering) -> Option<Ordering> {
202 (*self as int).partial_cmp(&(*other as int))
206 /// Trait for values that can be compared for a sort-order.
208 /// The comparison must satisfy, for all `a`, `b` and `c`:
210 /// - antisymmetry: if `a < b` then `!(a > b)` and vice versa; and
211 /// - transitivity: `a < b` and `b < c` implies `a < c`. The same must hold for
212 /// both `==` and `>`.
214 /// Note that these requirements mean that the trait itself must be
215 /// implemented symmetrically and transitively: if `T: PartialOrd<U>`
216 /// and `U: PartialOrd<V>` then `U: PartialOrd<T>` and `T:
219 /// PartialOrd only requires implementation of the `partial_cmp` method,
220 /// with the others generated from default implementations.
222 /// However it remains possible to implement the others separately for types
223 /// which do not have a total order. For example, for floating point numbers,
224 /// `NaN < 0 == false` and `NaN >= 0 == false` (cf. IEEE 754-2008 section
228 pub trait PartialOrd<Sized? Rhs = Self> for Sized?: PartialEq<Rhs> {
229 /// This method returns an ordering between `self` and `other` values
232 fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>;
234 /// This method tests less than (for `self` and `other`) and is used by the `<` operator.
237 fn lt(&self, other: &Rhs) -> bool {
238 match self.partial_cmp(other) {
244 /// This method tests less than or equal to (`<=`).
247 fn le(&self, other: &Rhs) -> bool {
248 match self.partial_cmp(other) {
249 Some(Less) | Some(Equal) => true,
254 /// This method tests greater than (`>`).
257 fn gt(&self, other: &Rhs) -> bool {
258 match self.partial_cmp(other) {
259 Some(Greater) => true,
264 /// This method tests greater than or equal to (`>=`).
267 fn ge(&self, other: &Rhs) -> bool {
268 match self.partial_cmp(other) {
269 Some(Greater) | Some(Equal) => true,
275 /// Compare and return the minimum of two values.
278 pub fn min<T: Ord>(v1: T, v2: T) -> T {
279 if v1 < v2 { v1 } else { v2 }
282 /// Compare and return the maximum of two values.
285 pub fn max<T: Ord>(v1: T, v2: T) -> T {
286 if v1 > v2 { v1 } else { v2 }
289 /// Compare and return the minimum of two values if there is one.
291 /// Returns the first argument if the comparison determines them to be equal.
294 pub fn partial_min<T: PartialOrd>(v1: T, v2: T) -> Option<T> {
295 match v1.partial_cmp(&v2) {
296 Some(Less) | Some(Equal) => Some(v1),
297 Some(Greater) => Some(v2),
302 /// Compare and return the maximum of two values if there is one.
304 /// Returns the first argument if the comparison determines them to be equal.
307 pub fn partial_max<T: PartialOrd>(v1: T, v2: T) -> Option<T> {
308 match v1.partial_cmp(&v2) {
309 Some(Less) => Some(v2),
310 Some(Equal) | Some(Greater) => Some(v1),
315 // Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types
317 use cmp::{PartialOrd, Ord, PartialEq, Eq, Ordering};
318 use cmp::Ordering::{Less, Greater, Equal};
321 use option::Option::{Some, None};
323 macro_rules! partial_eq_impl {
326 impl PartialEq for $t {
328 fn eq(&self, other: &$t) -> bool { (*self) == (*other) }
330 fn ne(&self, other: &$t) -> bool { (*self) != (*other) }
336 impl PartialEq for () {
338 fn eq(&self, _other: &()) -> bool { true }
340 fn ne(&self, _other: &()) -> bool { false }
344 bool char uint u8 u16 u32 u64 int i8 i16 i32 i64 f32 f64
347 macro_rules! eq_impl {
354 eq_impl! { () bool char uint u8 u16 u32 u64 int i8 i16 i32 i64 }
356 macro_rules! partial_ord_impl {
359 impl PartialOrd for $t {
361 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
362 match (self <= other, self >= other) {
363 (false, false) => None,
364 (false, true) => Some(Greater),
365 (true, false) => Some(Less),
366 (true, true) => Some(Equal),
370 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
372 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
374 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
376 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
382 impl PartialOrd for () {
384 fn partial_cmp(&self, _: &()) -> Option<Ordering> {
390 impl PartialOrd for bool {
392 fn partial_cmp(&self, other: &bool) -> Option<Ordering> {
393 (*self as u8).partial_cmp(&(*other as u8))
397 partial_ord_impl! { char uint u8 u16 u32 u64 int i8 i16 i32 i64 f32 f64 }
399 macro_rules! ord_impl {
404 fn cmp(&self, other: &$t) -> Ordering {
405 if *self < *other { Less }
406 else if *self > *other { Greater }
416 fn cmp(&self, _other: &()) -> Ordering { Equal }
422 fn cmp(&self, other: &bool) -> Ordering {
423 (*self as u8).cmp(&(*other as u8))
427 ord_impl! { char uint u8 u16 u32 u64 int i8 i16 i32 i64 }
432 impl<'a, 'b, Sized? A, Sized? B> PartialEq<&'b B> for &'a A where A: PartialEq<B> {
434 fn eq(&self, other: & &'b B) -> bool { PartialEq::eq(*self, *other) }
436 fn ne(&self, other: & &'b B) -> bool { PartialEq::ne(*self, *other) }
439 impl<'a, 'b, Sized? A, Sized? B> PartialOrd<&'b B> for &'a A where A: PartialOrd<B> {
441 fn partial_cmp(&self, other: &&'b B) -> Option<Ordering> {
442 PartialOrd::partial_cmp(*self, *other)
445 fn lt(&self, other: & &'b B) -> bool { PartialOrd::lt(*self, *other) }
447 fn le(&self, other: & &'b B) -> bool { PartialOrd::le(*self, *other) }
449 fn ge(&self, other: & &'b B) -> bool { PartialOrd::ge(*self, *other) }
451 fn gt(&self, other: & &'b B) -> bool { PartialOrd::gt(*self, *other) }
454 impl<'a, Sized? A> Ord for &'a A where A: Ord {
456 fn cmp(&self, other: & &'a A) -> Ordering { Ord::cmp(*self, *other) }
459 impl<'a, Sized? A> Eq for &'a A where A: Eq {}
464 impl<'a, 'b, Sized? A, Sized? B> PartialEq<&'b mut B> for &'a mut A where A: PartialEq<B> {
466 fn eq(&self, other: &&'b mut B) -> bool { PartialEq::eq(*self, *other) }
468 fn ne(&self, other: &&'b mut B) -> bool { PartialEq::ne(*self, *other) }
471 impl<'a, 'b, Sized? A, Sized? B> PartialOrd<&'b mut B> for &'a mut A where A: PartialOrd<B> {
473 fn partial_cmp(&self, other: &&'b mut B) -> Option<Ordering> {
474 PartialOrd::partial_cmp(*self, *other)
477 fn lt(&self, other: &&'b mut B) -> bool { PartialOrd::lt(*self, *other) }
479 fn le(&self, other: &&'b mut B) -> bool { PartialOrd::le(*self, *other) }
481 fn ge(&self, other: &&'b mut B) -> bool { PartialOrd::ge(*self, *other) }
483 fn gt(&self, other: &&'b mut B) -> bool { PartialOrd::gt(*self, *other) }
486 impl<'a, Sized? A> Ord for &'a mut A where A: Ord {
488 fn cmp(&self, other: &&'a mut A) -> Ordering { Ord::cmp(*self, *other) }
491 impl<'a, Sized? A> Eq for &'a mut A where A: Eq {}
494 impl<'a, 'b, Sized? A, Sized? B> PartialEq<&'b mut B> for &'a A where A: PartialEq<B> {
496 fn eq(&self, other: &&'b mut B) -> bool { PartialEq::eq(*self, *other) }
498 fn ne(&self, other: &&'b mut B) -> bool { PartialEq::ne(*self, *other) }
502 impl<'a, 'b, Sized? A, Sized? B> PartialEq<&'b B> for &'a mut A where A: PartialEq<B> {
504 fn eq(&self, other: &&'b B) -> bool { PartialEq::eq(*self, *other) }
506 fn ne(&self, other: &&'b B) -> bool { PartialEq::ne(*self, *other) }