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::{mod, 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
72 pub trait PartialEq<Sized? Rhs = Self> for Sized? {
73 /// This method tests for `self` and `other` values to be equal, and is used by `==`.
75 fn eq(&self, other: &Rhs) -> bool;
77 /// This method tests for `!=`.
80 fn ne(&self, other: &Rhs) -> bool { !self.eq(other) }
83 /// Trait for equality comparisons which are [equivalence relations](
84 /// https://en.wikipedia.org/wiki/Equivalence_relation).
86 /// This means, that in addition to `a == b` and `a != b` being strict
87 /// inverses, the equality must be (for all `a`, `b` and `c`):
89 /// - reflexive: `a == a`;
90 /// - symmetric: `a == b` implies `b == a`; and
91 /// - transitive: `a == b` and `b == c` implies `a == c`.
93 pub trait Eq for Sized?: PartialEq<Self> {
94 // FIXME #13101: this method is used solely by #[deriving] to
95 // assert that every component of a type implements #[deriving]
96 // itself, the current deriving infrastructure means doing this
97 // assertion without using a method on this trait is nearly
100 // This should never be implemented by hand.
103 fn assert_receiver_is_total_eq(&self) {}
106 /// An ordering is, e.g, a result of a comparison between two values.
107 #[deriving(Clone, Copy, PartialEq, Show)]
110 /// An ordering where a compared value is less [than another].
113 /// An ordering where a compared value is equal [to another].
116 /// An ordering where a compared value is greater [than another].
122 /// Reverse the `Ordering`, so that `Less` becomes `Greater` and
128 /// assert_eq!(Less.reverse(), Greater);
129 /// assert_eq!(Equal.reverse(), Equal);
130 /// assert_eq!(Greater.reverse(), Less);
133 /// let mut data: &mut [_] = &mut [2u, 10, 5, 8];
135 /// // sort the array from largest to smallest.
136 /// data.sort_by(|a, b| a.cmp(b).reverse());
138 /// let b: &mut [_] = &mut [10u, 8, 5, 2];
139 /// assert!(data == b);
143 pub fn reverse(self) -> Ordering {
145 // this compiles really nicely (to a single instruction);
146 // an explicit match has a pile of branches and
149 // NB. it is safe because of the explicit discriminants
151 ::mem::transmute::<_, Ordering>(-(self as i8))
156 /// Trait for types that form a [total order](
157 /// https://en.wikipedia.org/wiki/Total_order).
159 /// An order is a total order if it is (for all `a`, `b` and `c`):
161 /// - total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is
163 /// - transitive, `a < b` and `b < c` implies `a < c`. The same must hold for
164 /// both `==` and `>`.
166 pub trait Ord for Sized?: Eq + PartialOrd<Self> {
167 /// This method returns an ordering between `self` and `other` values.
169 /// By convention, `self.cmp(&other)` returns the ordering matching
170 /// the expression `self <operator> other` if true. For example:
173 /// assert_eq!( 5u.cmp(&10), Less); // because 5 < 10
174 /// assert_eq!(10u.cmp(&5), Greater); // because 10 > 5
175 /// assert_eq!( 5u.cmp(&5), Equal); // because 5 == 5
178 fn cmp(&self, other: &Self) -> Ordering;
182 impl Eq for Ordering {}
185 impl Ord for Ordering {
188 fn cmp(&self, other: &Ordering) -> Ordering {
189 (*self as int).cmp(&(*other as int))
194 impl PartialOrd for Ordering {
197 fn partial_cmp(&self, other: &Ordering) -> Option<Ordering> {
198 (*self as int).partial_cmp(&(*other as int))
202 /// Trait for values that can be compared for a sort-order.
204 /// The comparison must satisfy, for all `a`, `b` and `c`:
206 /// - antisymmetry: if `a < b` then `!(a > b)` and vice versa; and
207 /// - transitivity: `a < b` and `b < c` implies `a < c`. The same must hold for
208 /// both `==` and `>`.
210 /// Note that these requirements mean that the trait itself must be
211 /// implemented symmetrically and transitively: if `T: PartialOrd<U>`
212 /// and `U: PartialOrd<V>` then `U: PartialOrd<T>` and `T:
215 /// PartialOrd only requires implementation of the `partial_cmp` method,
216 /// with the others generated from default implementations.
218 /// However it remains possible to implement the others separately for types
219 /// which do not have a total order. For example, for floating point numbers,
220 /// `NaN < 0 == false` and `NaN >= 0 == false` (cf. IEEE 754-2008 section
224 pub trait PartialOrd<Sized? Rhs = Self> for Sized?: PartialEq<Rhs> {
225 /// This method returns an ordering between `self` and `other` values
228 fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>;
230 /// This method tests less than (for `self` and `other`) and is used by the `<` operator.
233 fn lt(&self, other: &Rhs) -> bool {
234 match self.partial_cmp(other) {
240 /// This method tests less than or equal to (`<=`).
243 fn le(&self, other: &Rhs) -> bool {
244 match self.partial_cmp(other) {
245 Some(Less) | Some(Equal) => true,
250 /// This method tests greater than (`>`).
253 fn gt(&self, other: &Rhs) -> bool {
254 match self.partial_cmp(other) {
255 Some(Greater) => true,
260 /// This method tests greater than or equal to (`>=`).
263 fn ge(&self, other: &Rhs) -> bool {
264 match self.partial_cmp(other) {
265 Some(Greater) | Some(Equal) => true,
271 /// The equivalence relation. Two values may be equivalent even if they are
272 /// of different types. The most common use case for this relation is
273 /// container types; e.g. it is often desirable to be able to use `&str`
274 /// values to look up entries in a container with `String` keys.
275 #[deprecated = "Use overloaded core::cmp::PartialEq"]
276 pub trait Equiv<Sized? T> for Sized? {
277 /// Implement this function to decide equivalent values.
278 fn equiv(&self, other: &T) -> bool;
281 /// Compare and return the minimum of two values.
284 pub fn min<T: Ord>(v1: T, v2: T) -> T {
285 if v1 < v2 { v1 } else { v2 }
288 /// Compare and return the maximum of two values.
291 pub fn max<T: Ord>(v1: T, v2: T) -> T {
292 if v1 > v2 { v1 } else { v2 }
295 /// Compare and return the minimum of two values if there is one.
297 /// Returns the first argument if the comparison determines them to be equal.
300 pub fn partial_min<T: PartialOrd>(v1: T, v2: T) -> Option<T> {
301 match v1.partial_cmp(&v2) {
302 Some(Less) | Some(Equal) => Some(v1),
303 Some(Greater) => Some(v2),
308 /// Compare and return the maximum of two values if there is one.
310 /// Returns the first argument if the comparison determines them to be equal.
313 pub fn partial_max<T: PartialOrd>(v1: T, v2: T) -> Option<T> {
314 match v1.partial_cmp(&v2) {
315 Some(Less) => Some(v2),
316 Some(Equal) | Some(Greater) => Some(v1),
321 // Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types
323 use cmp::{PartialOrd, Ord, PartialEq, Eq, Ordering};
324 use cmp::Ordering::{Less, Greater, Equal};
327 use option::Option::{Some, None};
329 macro_rules! partial_eq_impl {
332 impl PartialEq for $t {
334 fn eq(&self, other: &$t) -> bool { (*self) == (*other) }
336 fn ne(&self, other: &$t) -> bool { (*self) != (*other) }
342 impl PartialEq for () {
344 fn eq(&self, _other: &()) -> bool { true }
346 fn ne(&self, _other: &()) -> bool { false }
350 bool char uint u8 u16 u32 u64 int i8 i16 i32 i64 f32 f64
353 macro_rules! eq_impl {
360 eq_impl! { () bool char uint u8 u16 u32 u64 int i8 i16 i32 i64 }
362 macro_rules! partial_ord_impl {
365 impl PartialOrd for $t {
367 fn partial_cmp(&self, other: &$t) -> Option<Ordering> {
368 match (self <= other, self >= other) {
369 (false, false) => None,
370 (false, true) => Some(Greater),
371 (true, false) => Some(Less),
372 (true, true) => Some(Equal),
376 fn lt(&self, other: &$t) -> bool { (*self) < (*other) }
378 fn le(&self, other: &$t) -> bool { (*self) <= (*other) }
380 fn ge(&self, other: &$t) -> bool { (*self) >= (*other) }
382 fn gt(&self, other: &$t) -> bool { (*self) > (*other) }
388 impl PartialOrd for () {
390 fn partial_cmp(&self, _: &()) -> Option<Ordering> {
396 impl PartialOrd for bool {
398 fn partial_cmp(&self, other: &bool) -> Option<Ordering> {
399 (*self as u8).partial_cmp(&(*other as u8))
403 partial_ord_impl! { char uint u8 u16 u32 u64 int i8 i16 i32 i64 f32 f64 }
405 macro_rules! ord_impl {
410 fn cmp(&self, other: &$t) -> Ordering {
411 if *self < *other { Less }
412 else if *self > *other { Greater }
422 fn cmp(&self, _other: &()) -> Ordering { Equal }
428 fn cmp(&self, other: &bool) -> Ordering {
429 (*self as u8).cmp(&(*other as u8))
433 ord_impl! { char uint u8 u16 u32 u64 int i8 i16 i32 i64 }
438 impl<'a, 'b, Sized? A, Sized? B> PartialEq<&'b B> for &'a A where A: PartialEq<B> {
440 fn eq(&self, other: & &'b B) -> bool { PartialEq::eq(*self, *other) }
442 fn ne(&self, other: & &'b B) -> bool { PartialEq::ne(*self, *other) }
445 impl<'a, 'b, Sized? A, Sized? B> PartialOrd<&'b B> for &'a A where A: PartialOrd<B> {
447 fn partial_cmp(&self, other: &&'b B) -> Option<Ordering> {
448 PartialOrd::partial_cmp(*self, *other)
451 fn lt(&self, other: & &'b B) -> bool { PartialOrd::lt(*self, *other) }
453 fn le(&self, other: & &'b B) -> bool { PartialOrd::le(*self, *other) }
455 fn ge(&self, other: & &'b B) -> bool { PartialOrd::ge(*self, *other) }
457 fn gt(&self, other: & &'b B) -> bool { PartialOrd::gt(*self, *other) }
460 impl<'a, Sized? A> Ord for &'a A where A: Ord {
462 fn cmp(&self, other: & &'a A) -> Ordering { Ord::cmp(*self, *other) }
465 impl<'a, Sized? A> Eq for &'a A where A: Eq {}
470 impl<'a, 'b, Sized? A, Sized? B> PartialEq<&'b mut B> for &'a mut A where A: PartialEq<B> {
472 fn eq(&self, other: &&'b mut B) -> bool { PartialEq::eq(*self, *other) }
474 fn ne(&self, other: &&'b mut B) -> bool { PartialEq::ne(*self, *other) }
477 impl<'a, 'b, Sized? A, Sized? B> PartialOrd<&'b mut B> for &'a mut A where A: PartialOrd<B> {
479 fn partial_cmp(&self, other: &&'b mut B) -> Option<Ordering> {
480 PartialOrd::partial_cmp(*self, *other)
483 fn lt(&self, other: &&'b mut B) -> bool { PartialOrd::lt(*self, *other) }
485 fn le(&self, other: &&'b mut B) -> bool { PartialOrd::le(*self, *other) }
487 fn ge(&self, other: &&'b mut B) -> bool { PartialOrd::ge(*self, *other) }
489 fn gt(&self, other: &&'b mut B) -> bool { PartialOrd::gt(*self, *other) }
492 impl<'a, Sized? A> Ord for &'a mut A where A: Ord {
494 fn cmp(&self, other: &&'a mut A) -> Ordering { Ord::cmp(*self, *other) }
497 impl<'a, Sized? A> Eq for &'a mut A where A: Eq {}
500 impl<'a, 'b, Sized? A, Sized? B> PartialEq<&'b mut B> for &'a A where A: PartialEq<B> {
502 fn eq(&self, other: &&'b mut B) -> bool { PartialEq::eq(*self, *other) }
504 fn ne(&self, other: &&'b mut B) -> bool { PartialEq::ne(*self, *other) }
508 impl<'a, 'b, Sized? A, Sized? B> PartialEq<&'b B> for &'a mut A where A: PartialEq<B> {
510 fn eq(&self, other: &&'b B) -> bool { PartialEq::eq(*self, *other) }
512 fn ne(&self, other: &&'b B) -> bool { PartialEq::ne(*self, *other) }