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diff --git a/library/core/src/cmp.rs b/library/core/src/cmp.rs new file mode 100644 index 00000000000..79085740119 --- /dev/null +++ b/library/core/src/cmp.rs @@ -0,0 +1,1349 @@ +//! Functionality for ordering and comparison. +//! +//! This module contains various tools for ordering and comparing values. In +//! summary: +//! +//! * [`Eq`] and [`PartialEq`] are traits that allow you to define total and +//! partial equality between values, respectively. Implementing them overloads +//! the `==` and `!=` operators. +//! * [`Ord`] and [`PartialOrd`] are traits that allow you to define total and +//! partial orderings between values, respectively. Implementing them overloads +//! the `<`, `<=`, `>`, and `>=` operators. +//! * [`Ordering`] is an enum returned by the main functions of [`Ord`] and +//! [`PartialOrd`], and describes an ordering. +//! * [`Reverse`] is a struct that allows you to easily reverse an ordering. +//! * [`max`] and [`min`] are functions that build off of [`Ord`] and allow you +//! to find the maximum or minimum of two values. +//! +//! For more details, see the respective documentation of each item in the list. +//! +//! [`Eq`]: trait.Eq.html +//! [`PartialEq`]: trait.PartialEq.html +//! [`Ord`]: trait.Ord.html +//! [`PartialOrd`]: trait.PartialOrd.html +//! [`Ordering`]: enum.Ordering.html +//! [`Reverse`]: struct.Reverse.html +//! [`max`]: fn.max.html +//! [`min`]: fn.min.html + +#![stable(feature = "rust1", since = "1.0.0")] + +use self::Ordering::*; + +/// Trait for equality comparisons which are [partial equivalence +/// relations](http://en.wikipedia.org/wiki/Partial_equivalence_relation). +/// +/// This trait allows for partial equality, for types that do not have a full +/// equivalence relation. For example, in floating point numbers `NaN != NaN`, +/// so floating point types implement `PartialEq` but not [`Eq`](Eq). +/// +/// Formally, the equality must be (for all `a`, `b` and `c`): +/// +/// - symmetric: `a == b` implies `b == a`; and +/// - transitive: `a == b` and `b == c` implies `a == c`. +/// +/// Note that these requirements mean that the trait itself must be implemented +/// symmetrically and transitively: if `T: PartialEq<U>` and `U: PartialEq<V>` +/// then `U: PartialEq<T>` and `T: PartialEq<V>`. +/// +/// ## Derivable +/// +/// This trait can be used with `#[derive]`. When `derive`d on structs, two +/// instances are equal if all fields are equal, and not equal if any fields +/// are not equal. When `derive`d on enums, each variant is equal to itself +/// and not equal to the other variants. +/// +/// ## How can I implement `PartialEq`? +/// +/// `PartialEq` only requires the [`eq`] method to be implemented; [`ne`] is defined +/// in terms of it by default. Any manual implementation of [`ne`] *must* respect +/// the rule that [`eq`] is a strict inverse of [`ne`]; that is, `!(a == b)` if and +/// only if `a != b`. +/// +/// Implementations of `PartialEq`, [`PartialOrd`], and [`Ord`] *must* agree with +/// each other. It's easy to accidentally make them disagree by deriving some +/// of the traits and manually implementing others. +/// +/// An example implementation for a domain in which two books are considered +/// the same book if their ISBN matches, even if the formats differ: +/// +/// ``` +/// enum BookFormat { +/// Paperback, +/// Hardback, +/// Ebook, +/// } +/// +/// struct Book { +/// isbn: i32, +/// format: BookFormat, +/// } +/// +/// impl PartialEq for Book { +/// fn eq(&self, other: &Self) -> bool { +/// self.isbn == other.isbn +/// } +/// } +/// +/// let b1 = Book { isbn: 3, format: BookFormat::Paperback }; +/// let b2 = Book { isbn: 3, format: BookFormat::Ebook }; +/// let b3 = Book { isbn: 10, format: BookFormat::Paperback }; +/// +/// assert!(b1 == b2); +/// assert!(b1 != b3); +/// ``` +/// +/// ## How can I compare two different types? +/// +/// The type you can compare with is controlled by `PartialEq`'s type parameter. +/// For example, let's tweak our previous code a bit: +/// +/// ``` +/// // The derive implements <BookFormat> == <BookFormat> comparisons +/// #[derive(PartialEq)] +/// enum BookFormat { +/// Paperback, +/// Hardback, +/// Ebook, +/// } +/// +/// struct Book { +/// isbn: i32, +/// format: BookFormat, +/// } +/// +/// // Implement <Book> == <BookFormat> comparisons +/// impl PartialEq<BookFormat> for Book { +/// fn eq(&self, other: &BookFormat) -> bool { +/// self.format == *other +/// } +/// } +/// +/// // Implement <BookFormat> == <Book> comparisons +/// impl PartialEq<Book> for BookFormat { +/// fn eq(&self, other: &Book) -> bool { +/// *self == other.format +/// } +/// } +/// +/// let b1 = Book { isbn: 3, format: BookFormat::Paperback }; +/// +/// assert!(b1 == BookFormat::Paperback); +/// assert!(BookFormat::Ebook != b1); +/// ``` +/// +/// By changing `impl PartialEq for Book` to `impl PartialEq<BookFormat> for Book`, +/// we allow `BookFormat`s to be compared with `Book`s. +/// +/// A comparison like the one above, which ignores some fields of the struct, +/// can be dangerous. It can easily lead to an unintended violation of the +/// requirements for a partial equivalence relation. For example, if we kept +/// the above implementation of `PartialEq<Book>` for `BookFormat` and added an +/// implementation of `PartialEq<Book>` for `Book` (either via a `#[derive]` or +/// via the manual implementation from the first example) then the result would +/// violate transitivity: +/// +/// ```should_panic +/// #[derive(PartialEq)] +/// enum BookFormat { +/// Paperback, +/// Hardback, +/// Ebook, +/// } +/// +/// #[derive(PartialEq)] +/// struct Book { +/// isbn: i32, +/// format: BookFormat, +/// } +/// +/// impl PartialEq<BookFormat> for Book { +/// fn eq(&self, other: &BookFormat) -> bool { +/// self.format == *other +/// } +/// } +/// +/// impl PartialEq<Book> for BookFormat { +/// fn eq(&self, other: &Book) -> bool { +/// *self == other.format +/// } +/// } +/// +/// fn main() { +/// let b1 = Book { isbn: 1, format: BookFormat::Paperback }; +/// let b2 = Book { isbn: 2, format: BookFormat::Paperback }; +/// +/// assert!(b1 == BookFormat::Paperback); +/// assert!(BookFormat::Paperback == b2); +/// +/// // The following should hold by transitivity but doesn't. +/// assert!(b1 == b2); // <-- PANICS +/// } +/// ``` +/// +/// # Examples +/// +/// ``` +/// let x: u32 = 0; +/// let y: u32 = 1; +/// +/// assert_eq!(x == y, false); +/// assert_eq!(x.eq(&y), false); +/// ``` +/// +/// [`eq`]: PartialEq::eq +/// [`ne`]: PartialEq::ne +#[lang = "eq"] +#[stable(feature = "rust1", since = "1.0.0")] +#[doc(alias = "==")] +#[doc(alias = "!=")] +#[rustc_on_unimplemented( + message = "can't compare `{Self}` with `{Rhs}`", + label = "no implementation for `{Self} == {Rhs}`" +)] +pub trait PartialEq<Rhs: ?Sized = Self> { + /// This method tests for `self` and `other` values to be equal, and is used + /// by `==`. + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + fn eq(&self, other: &Rhs) -> bool; + + /// This method tests for `!=`. + #[inline] + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + fn ne(&self, other: &Rhs) -> bool { + !self.eq(other) + } +} + +/// Derive macro generating an impl of the trait `PartialEq`. +#[rustc_builtin_macro] +#[stable(feature = "builtin_macro_prelude", since = "1.38.0")] +#[allow_internal_unstable(core_intrinsics, structural_match)] +pub macro PartialEq($item:item) { + /* compiler built-in */ +} + +/// Trait for equality comparisons which are [equivalence relations]( +/// https://en.wikipedia.org/wiki/Equivalence_relation). +/// +/// This means, that in addition to `a == b` and `a != b` being strict inverses, the equality must +/// be (for all `a`, `b` and `c`): +/// +/// - reflexive: `a == a`; +/// - symmetric: `a == b` implies `b == a`; and +/// - transitive: `a == b` and `b == c` implies `a == c`. +/// +/// This property cannot be checked by the compiler, and therefore `Eq` implies +/// [`PartialEq`], and has no extra methods. +/// +/// ## Derivable +/// +/// This trait can be used with `#[derive]`. When `derive`d, because `Eq` has +/// no extra methods, it is only informing the compiler that this is an +/// equivalence relation rather than a partial equivalence relation. Note that +/// the `derive` strategy requires all fields are `Eq`, which isn't +/// always desired. +/// +/// ## How can I implement `Eq`? +/// +/// If you cannot use the `derive` strategy, specify that your type implements +/// `Eq`, which has no methods: +/// +/// ``` +/// enum BookFormat { Paperback, Hardback, Ebook } +/// struct Book { +/// isbn: i32, +/// format: BookFormat, +/// } +/// impl PartialEq for Book { +/// fn eq(&self, other: &Self) -> bool { +/// self.isbn == other.isbn +/// } +/// } +/// impl Eq for Book {} +/// ``` +#[doc(alias = "==")] +#[doc(alias = "!=")] +#[stable(feature = "rust1", since = "1.0.0")] +pub trait Eq: PartialEq<Self> { + // this method is used solely by #[deriving] to assert + // that every component of a type implements #[deriving] + // itself, the current deriving infrastructure means doing this + // assertion without using a method on this trait is nearly + // impossible. + // + // This should never be implemented by hand. + #[doc(hidden)] + #[inline] + #[stable(feature = "rust1", since = "1.0.0")] + fn assert_receiver_is_total_eq(&self) {} +} + +/// Derive macro generating an impl of the trait `Eq`. +#[rustc_builtin_macro] +#[stable(feature = "builtin_macro_prelude", since = "1.38.0")] +#[allow_internal_unstable(core_intrinsics, derive_eq, structural_match)] +pub macro Eq($item:item) { + /* compiler built-in */ +} + +// FIXME: this struct is used solely by #[derive] to +// assert that every component of a type implements Eq. +// +// This struct should never appear in user code. +#[doc(hidden)] +#[allow(missing_debug_implementations)] +#[unstable(feature = "derive_eq", reason = "deriving hack, should not be public", issue = "none")] +pub struct AssertParamIsEq<T: Eq + ?Sized> { + _field: crate::marker::PhantomData<T>, +} + +/// An `Ordering` is the result of a comparison between two values. +/// +/// # Examples +/// +/// ``` +/// use std::cmp::Ordering; +/// +/// let result = 1.cmp(&2); +/// assert_eq!(Ordering::Less, result); +/// +/// let result = 1.cmp(&1); +/// assert_eq!(Ordering::Equal, result); +/// +/// let result = 2.cmp(&1); +/// assert_eq!(Ordering::Greater, result); +/// ``` +#[derive(Clone, Copy, PartialEq, Debug, Hash)] +#[stable(feature = "rust1", since = "1.0.0")] +pub enum Ordering { + /// An ordering where a compared value is less than another. + #[stable(feature = "rust1", since = "1.0.0")] + Less = -1, + /// An ordering where a compared value is equal to another. + #[stable(feature = "rust1", since = "1.0.0")] + Equal = 0, + /// An ordering where a compared value is greater than another. + #[stable(feature = "rust1", since = "1.0.0")] + Greater = 1, +} + +impl Ordering { + /// Reverses the `Ordering`. + /// + /// * `Less` becomes `Greater`. + /// * `Greater` becomes `Less`. + /// * `Equal` becomes `Equal`. + /// + /// # Examples + /// + /// Basic behavior: + /// + /// ``` + /// use std::cmp::Ordering; + /// + /// assert_eq!(Ordering::Less.reverse(), Ordering::Greater); + /// assert_eq!(Ordering::Equal.reverse(), Ordering::Equal); + /// assert_eq!(Ordering::Greater.reverse(), Ordering::Less); + /// ``` + /// + /// This method can be used to reverse a comparison: + /// + /// ``` + /// let data: &mut [_] = &mut [2, 10, 5, 8]; + /// + /// // sort the array from largest to smallest. + /// data.sort_by(|a, b| a.cmp(b).reverse()); + /// + /// let b: &mut [_] = &mut [10, 8, 5, 2]; + /// assert!(data == b); + /// ``` + #[inline] + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn reverse(self) -> Ordering { + match self { + Less => Greater, + Equal => Equal, + Greater => Less, + } + } + + /// Chains two orderings. + /// + /// Returns `self` when it's not `Equal`. Otherwise returns `other`. + /// + /// # Examples + /// + /// ``` + /// use std::cmp::Ordering; + /// + /// let result = Ordering::Equal.then(Ordering::Less); + /// assert_eq!(result, Ordering::Less); + /// + /// let result = Ordering::Less.then(Ordering::Equal); + /// assert_eq!(result, Ordering::Less); + /// + /// let result = Ordering::Less.then(Ordering::Greater); + /// assert_eq!(result, Ordering::Less); + /// + /// let result = Ordering::Equal.then(Ordering::Equal); + /// assert_eq!(result, Ordering::Equal); + /// + /// let x: (i64, i64, i64) = (1, 2, 7); + /// let y: (i64, i64, i64) = (1, 5, 3); + /// let result = x.0.cmp(&y.0).then(x.1.cmp(&y.1)).then(x.2.cmp(&y.2)); + /// + /// assert_eq!(result, Ordering::Less); + /// ``` + #[inline] + #[must_use] + #[stable(feature = "ordering_chaining", since = "1.17.0")] + pub fn then(self, other: Ordering) -> Ordering { + match self { + Equal => other, + _ => self, + } + } + + /// Chains the ordering with the given function. + /// + /// Returns `self` when it's not `Equal`. Otherwise calls `f` and returns + /// the result. + /// + /// # Examples + /// + /// ``` + /// use std::cmp::Ordering; + /// + /// let result = Ordering::Equal.then_with(|| Ordering::Less); + /// assert_eq!(result, Ordering::Less); + /// + /// let result = Ordering::Less.then_with(|| Ordering::Equal); + /// assert_eq!(result, Ordering::Less); + /// + /// let result = Ordering::Less.then_with(|| Ordering::Greater); + /// assert_eq!(result, Ordering::Less); + /// + /// let result = Ordering::Equal.then_with(|| Ordering::Equal); + /// assert_eq!(result, Ordering::Equal); + /// + /// let x: (i64, i64, i64) = (1, 2, 7); + /// let y: (i64, i64, i64) = (1, 5, 3); + /// let result = x.0.cmp(&y.0).then_with(|| x.1.cmp(&y.1)).then_with(|| x.2.cmp(&y.2)); + /// + /// assert_eq!(result, Ordering::Less); + /// ``` + #[inline] + #[must_use] + #[stable(feature = "ordering_chaining", since = "1.17.0")] + pub fn then_with<F: FnOnce() -> Ordering>(self, f: F) -> Ordering { + match self { + Equal => f(), + _ => self, + } + } +} + +/// A helper struct for reverse ordering. +/// +/// This struct is a helper to be used with functions like [`Vec::sort_by_key`] and +/// can be used to reverse order a part of a key. +/// +/// [`Vec::sort_by_key`]: ../../std/vec/struct.Vec.html#method.sort_by_key +/// +/// # Examples +/// +/// ``` +/// use std::cmp::Reverse; +/// +/// let mut v = vec![1, 2, 3, 4, 5, 6]; +/// v.sort_by_key(|&num| (num > 3, Reverse(num))); +/// assert_eq!(v, vec![3, 2, 1, 6, 5, 4]); +/// ``` +#[derive(PartialEq, Eq, Debug, Copy, Clone, Default, Hash)] +#[stable(feature = "reverse_cmp_key", since = "1.19.0")] +pub struct Reverse<T>(#[stable(feature = "reverse_cmp_key", since = "1.19.0")] pub T); + +#[stable(feature = "reverse_cmp_key", since = "1.19.0")] +impl<T: PartialOrd> PartialOrd for Reverse<T> { + #[inline] + fn partial_cmp(&self, other: &Reverse<T>) -> Option<Ordering> { + other.0.partial_cmp(&self.0) + } + + #[inline] + fn lt(&self, other: &Self) -> bool { + other.0 < self.0 + } + #[inline] + fn le(&self, other: &Self) -> bool { + other.0 <= self.0 + } + #[inline] + fn gt(&self, other: &Self) -> bool { + other.0 > self.0 + } + #[inline] + fn ge(&self, other: &Self) -> bool { + other.0 >= self.0 + } +} + +#[stable(feature = "reverse_cmp_key", since = "1.19.0")] +impl<T: Ord> Ord for Reverse<T> { + #[inline] + fn cmp(&self, other: &Reverse<T>) -> Ordering { + other.0.cmp(&self.0) + } +} + +/// Trait for types that form a [total order](https://en.wikipedia.org/wiki/Total_order). +/// +/// An order is a total order if it is (for all `a`, `b` and `c`): +/// +/// - total and asymmetric: exactly one of `a < b`, `a == b` or `a > b` is true; and +/// - transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`. +/// +/// ## Derivable +/// +/// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a +/// lexicographic ordering based on the top-to-bottom declaration order of the struct's members. +/// When `derive`d on enums, variants are ordered by their top-to-bottom declaration order. +/// +/// ## How can I implement `Ord`? +/// +/// `Ord` requires that the type also be [`PartialOrd`] and [`Eq`] (which requires [`PartialEq`]). +/// +/// Then you must define an implementation for [`cmp`]. You may find it useful to use +/// [`cmp`] on your type's fields. +/// +/// Implementations of [`PartialEq`], [`PartialOrd`], and `Ord` *must* +/// agree with each other. That is, `a.cmp(b) == Ordering::Equal` if +/// and only if `a == b` and `Some(a.cmp(b)) == a.partial_cmp(b)` for +/// all `a` and `b`. It's easy to accidentally make them disagree by +/// deriving some of the traits and manually implementing others. +/// +/// Here's an example where you want to sort people by height only, disregarding `id` +/// and `name`: +/// +/// ``` +/// use std::cmp::Ordering; +/// +/// #[derive(Eq)] +/// struct Person { +/// id: u32, +/// name: String, +/// height: u32, +/// } +/// +/// impl Ord for Person { +/// fn cmp(&self, other: &Self) -> Ordering { +/// self.height.cmp(&other.height) +/// } +/// } +/// +/// impl PartialOrd for Person { +/// fn partial_cmp(&self, other: &Self) -> Option<Ordering> { +/// Some(self.cmp(other)) +/// } +/// } +/// +/// impl PartialEq for Person { +/// fn eq(&self, other: &Self) -> bool { +/// self.height == other.height +/// } +/// } +/// ``` +/// +/// [`cmp`]: Ord::cmp +#[doc(alias = "<")] +#[doc(alias = ">")] +#[doc(alias = "<=")] +#[doc(alias = ">=")] +#[stable(feature = "rust1", since = "1.0.0")] +pub trait Ord: Eq + PartialOrd<Self> { + /// This method returns an [`Ordering`] between `self` and `other`. + /// + /// By convention, `self.cmp(&other)` returns the ordering matching the expression + /// `self <operator> other` if true. + /// + /// # Examples + /// + /// ``` + /// use std::cmp::Ordering; + /// + /// assert_eq!(5.cmp(&10), Ordering::Less); + /// assert_eq!(10.cmp(&5), Ordering::Greater); + /// assert_eq!(5.cmp(&5), Ordering::Equal); + /// ``` + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + fn cmp(&self, other: &Self) -> Ordering; + + /// Compares and returns the maximum of two values. + /// + /// Returns the second argument if the comparison determines them to be equal. + /// + /// # Examples + /// + /// ``` + /// assert_eq!(2, 1.max(2)); + /// assert_eq!(2, 2.max(2)); + /// ``` + #[stable(feature = "ord_max_min", since = "1.21.0")] + #[inline] + #[must_use] + fn max(self, other: Self) -> Self + where + Self: Sized, + { + max_by(self, other, Ord::cmp) + } + + /// Compares and returns the minimum of two values. + /// + /// Returns the first argument if the comparison determines them to be equal. + /// + /// # Examples + /// + /// ``` + /// assert_eq!(1, 1.min(2)); + /// assert_eq!(2, 2.min(2)); + /// ``` + #[stable(feature = "ord_max_min", since = "1.21.0")] + #[inline] + #[must_use] + fn min(self, other: Self) -> Self + where + Self: Sized, + { + min_by(self, other, Ord::cmp) + } + + /// Restrict a value to a certain interval. + /// + /// Returns `max` if `self` is greater than `max`, and `min` if `self` is + /// less than `min`. Otherwise this returns `self`. + /// + /// # Panics + /// + /// Panics if `min > max`. + /// + /// # Examples + /// + /// ``` + /// #![feature(clamp)] + /// + /// assert!((-3).clamp(-2, 1) == -2); + /// assert!(0.clamp(-2, 1) == 0); + /// assert!(2.clamp(-2, 1) == 1); + /// ``` + #[must_use] + #[unstable(feature = "clamp", issue = "44095")] + fn clamp(self, min: Self, max: Self) -> Self + where + Self: Sized, + { + assert!(min <= max); + if self < min { + min + } else if self > max { + max + } else { + self + } + } +} + +/// Derive macro generating an impl of the trait `Ord`. +#[rustc_builtin_macro] +#[stable(feature = "builtin_macro_prelude", since = "1.38.0")] +#[allow_internal_unstable(core_intrinsics)] +pub macro Ord($item:item) { + /* compiler built-in */ +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl Eq for Ordering {} + +#[stable(feature = "rust1", since = "1.0.0")] +impl Ord for Ordering { + #[inline] + fn cmp(&self, other: &Ordering) -> Ordering { + (*self as i32).cmp(&(*other as i32)) + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl PartialOrd for Ordering { + #[inline] + fn partial_cmp(&self, other: &Ordering) -> Option<Ordering> { + (*self as i32).partial_cmp(&(*other as i32)) + } +} + +/// Trait for values that can be compared for a sort-order. +/// +/// The comparison must satisfy, for all `a`, `b` and `c`: +/// +/// - asymmetry: if `a < b` then `!(a > b)`, as well as `a > b` implying `!(a < b)`; and +/// - transitivity: `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`. +/// +/// Note that these requirements mean that the trait itself must be implemented symmetrically and +/// transitively: if `T: PartialOrd<U>` and `U: PartialOrd<V>` then `U: PartialOrd<T>` and `T: +/// PartialOrd<V>`. +/// +/// ## Derivable +/// +/// This trait can be used with `#[derive]`. When `derive`d on structs, it will produce a +/// lexicographic ordering based on the top-to-bottom declaration order of the struct's members. +/// When `derive`d on enums, variants are ordered by their top-to-bottom declaration order. +/// +/// ## How can I implement `PartialOrd`? +/// +/// `PartialOrd` only requires implementation of the [`partial_cmp`] method, with the others +/// generated from default implementations. +/// +/// However it remains possible to implement the others separately for types which do not have a +/// total order. For example, for floating point numbers, `NaN < 0 == false` and `NaN >= 0 == +/// false` (cf. IEEE 754-2008 section 5.11). +/// +/// `PartialOrd` requires your type to be [`PartialEq`]. +/// +/// Implementations of [`PartialEq`], `PartialOrd`, and [`Ord`] *must* agree with each other. It's +/// easy to accidentally make them disagree by deriving some of the traits and manually +/// implementing others. +/// +/// If your type is [`Ord`], you can implement [`partial_cmp`] by using [`cmp`]: +/// +/// ``` +/// use std::cmp::Ordering; +/// +/// #[derive(Eq)] +/// struct Person { +/// id: u32, +/// name: String, +/// height: u32, +/// } +/// +/// impl PartialOrd for Person { +/// fn partial_cmp(&self, other: &Person) -> Option<Ordering> { +/// Some(self.cmp(other)) +/// } +/// } +/// +/// impl Ord for Person { +/// fn cmp(&self, other: &Person) -> Ordering { +/// self.height.cmp(&other.height) +/// } +/// } +/// +/// impl PartialEq for Person { +/// fn eq(&self, other: &Person) -> bool { +/// self.height == other.height +/// } +/// } +/// ``` +/// +/// You may also find it useful to use [`partial_cmp`] on your type's fields. Here +/// is an example of `Person` types who have a floating-point `height` field that +/// is the only field to be used for sorting: +/// +/// ``` +/// use std::cmp::Ordering; +/// +/// struct Person { +/// id: u32, +/// name: String, +/// height: f64, +/// } +/// +/// impl PartialOrd for Person { +/// fn partial_cmp(&self, other: &Self) -> Option<Ordering> { +/// self.height.partial_cmp(&other.height) +/// } +/// } +/// +/// impl PartialEq for Person { +/// fn eq(&self, other: &Self) -> bool { +/// self.height == other.height +/// } +/// } +/// ``` +/// +/// # Examples +/// +/// ``` +/// let x : u32 = 0; +/// let y : u32 = 1; +/// +/// assert_eq!(x < y, true); +/// assert_eq!(x.lt(&y), true); +/// ``` +/// +/// [`partial_cmp`]: PartialOrd::partial_cmp +/// [`cmp`]: Ord::cmp +#[lang = "partial_ord"] +#[stable(feature = "rust1", since = "1.0.0")] +#[doc(alias = ">")] +#[doc(alias = "<")] +#[doc(alias = "<=")] +#[doc(alias = ">=")] +#[rustc_on_unimplemented( + message = "can't compare `{Self}` with `{Rhs}`", + label = "no implementation for `{Self} < {Rhs}` and `{Self} > {Rhs}`" +)] +pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> { + /// This method returns an ordering between `self` and `other` values if one exists. + /// + /// # Examples + /// + /// ``` + /// use std::cmp::Ordering; + /// + /// let result = 1.0.partial_cmp(&2.0); + /// assert_eq!(result, Some(Ordering::Less)); + /// + /// let result = 1.0.partial_cmp(&1.0); + /// assert_eq!(result, Some(Ordering::Equal)); + /// + /// let result = 2.0.partial_cmp(&1.0); + /// assert_eq!(result, Some(Ordering::Greater)); + /// ``` + /// + /// When comparison is impossible: + /// + /// ``` + /// let result = f64::NAN.partial_cmp(&1.0); + /// assert_eq!(result, None); + /// ``` + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>; + + /// This method tests less than (for `self` and `other`) and is used by the `<` operator. + /// + /// # Examples + /// + /// ``` + /// let result = 1.0 < 2.0; + /// assert_eq!(result, true); + /// + /// let result = 2.0 < 1.0; + /// assert_eq!(result, false); + /// ``` + #[inline] + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + fn lt(&self, other: &Rhs) -> bool { + matches!(self.partial_cmp(other), Some(Less)) + } + + /// This method tests less than or equal to (for `self` and `other`) and is used by the `<=` + /// operator. + /// + /// # Examples + /// + /// ``` + /// let result = 1.0 <= 2.0; + /// assert_eq!(result, true); + /// + /// let result = 2.0 <= 2.0; + /// assert_eq!(result, true); + /// ``` + #[inline] + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + fn le(&self, other: &Rhs) -> bool { + matches!(self.partial_cmp(other), Some(Less | Equal)) + } + + /// This method tests greater than (for `self` and `other`) and is used by the `>` operator. + /// + /// # Examples + /// + /// ``` + /// let result = 1.0 > 2.0; + /// assert_eq!(result, false); + /// + /// let result = 2.0 > 2.0; + /// assert_eq!(result, false); + /// ``` + #[inline] + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + fn gt(&self, other: &Rhs) -> bool { + matches!(self.partial_cmp(other), Some(Greater)) + } + + /// This method tests greater than or equal to (for `self` and `other`) and is used by the `>=` + /// operator. + /// + /// # Examples + /// + /// ``` + /// let result = 2.0 >= 1.0; + /// assert_eq!(result, true); + /// + /// let result = 2.0 >= 2.0; + /// assert_eq!(result, true); + /// ``` + #[inline] + #[must_use] + #[stable(feature = "rust1", since = "1.0.0")] + fn ge(&self, other: &Rhs) -> bool { + matches!(self.partial_cmp(other), Some(Greater | Equal)) + } +} + +/// Derive macro generating an impl of the trait `PartialOrd`. +#[rustc_builtin_macro] +#[stable(feature = "builtin_macro_prelude", since = "1.38.0")] +#[allow_internal_unstable(core_intrinsics)] +pub macro PartialOrd($item:item) { + /* compiler built-in */ +} + +/// Compares and returns the minimum of two values. +/// +/// Returns the first argument if the comparison determines them to be equal. +/// +/// Internally uses an alias to [`Ord::min`]. +/// +/// # Examples +/// +/// ``` +/// use std::cmp; +/// +/// assert_eq!(1, cmp::min(1, 2)); +/// assert_eq!(2, cmp::min(2, 2)); +/// ``` +#[inline] +#[must_use] +#[stable(feature = "rust1", since = "1.0.0")] +pub fn min<T: Ord>(v1: T, v2: T) -> T { + v1.min(v2) +} + +/// Returns the minimum of two values with respect to the specified comparison function. +/// +/// Returns the first argument if the comparison determines them to be equal. +/// +/// # Examples +/// +/// ``` +/// #![feature(cmp_min_max_by)] +/// +/// use std::cmp; +/// +/// assert_eq!(cmp::min_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), 1); +/// assert_eq!(cmp::min_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), -2); +/// ``` +#[inline] +#[must_use] +#[unstable(feature = "cmp_min_max_by", issue = "64460")] +pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T { + match compare(&v1, &v2) { + Ordering::Less | Ordering::Equal => v1, + Ordering::Greater => v2, + } +} + +/// Returns the element that gives the minimum value from the specified function. +/// +/// Returns the first argument if the comparison determines them to be equal. +/// +/// # Examples +/// +/// ``` +/// #![feature(cmp_min_max_by)] +/// +/// use std::cmp; +/// +/// assert_eq!(cmp::min_by_key(-2, 1, |x: &i32| x.abs()), 1); +/// assert_eq!(cmp::min_by_key(-2, 2, |x: &i32| x.abs()), -2); +/// ``` +#[inline] +#[must_use] +#[unstable(feature = "cmp_min_max_by", issue = "64460")] +pub fn min_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T { + min_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2))) +} + +/// Compares and returns the maximum of two values. +/// +/// Returns the second argument if the comparison determines them to be equal. +/// +/// Internally uses an alias to [`Ord::max`]. +/// +/// # Examples +/// +/// ``` +/// use std::cmp; +/// +/// assert_eq!(2, cmp::max(1, 2)); +/// assert_eq!(2, cmp::max(2, 2)); +/// ``` +#[inline] +#[must_use] +#[stable(feature = "rust1", since = "1.0.0")] +pub fn max<T: Ord>(v1: T, v2: T) -> T { + v1.max(v2) +} + +/// Returns the maximum of two values with respect to the specified comparison function. +/// +/// Returns the second argument if the comparison determines them to be equal. +/// +/// # Examples +/// +/// ``` +/// #![feature(cmp_min_max_by)] +/// +/// use std::cmp; +/// +/// assert_eq!(cmp::max_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), -2); +/// assert_eq!(cmp::max_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), 2); +/// ``` +#[inline] +#[must_use] +#[unstable(feature = "cmp_min_max_by", issue = "64460")] +pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T { + match compare(&v1, &v2) { + Ordering::Less | Ordering::Equal => v2, + Ordering::Greater => v1, + } +} + +/// Returns the element that gives the maximum value from the specified function. +/// +/// Returns the second argument if the comparison determines them to be equal. +/// +/// # Examples +/// +/// ``` +/// #![feature(cmp_min_max_by)] +/// +/// use std::cmp; +/// +/// assert_eq!(cmp::max_by_key(-2, 1, |x: &i32| x.abs()), -2); +/// assert_eq!(cmp::max_by_key(-2, 2, |x: &i32| x.abs()), 2); +/// ``` +#[inline] +#[must_use] +#[unstable(feature = "cmp_min_max_by", issue = "64460")] +pub fn max_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T { + max_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2))) +} + +// Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types +mod impls { + use crate::cmp::Ordering::{self, Equal, Greater, Less}; + use crate::hint::unreachable_unchecked; + + macro_rules! partial_eq_impl { + ($($t:ty)*) => ($( + #[stable(feature = "rust1", since = "1.0.0")] + impl PartialEq for $t { + #[inline] + fn eq(&self, other: &$t) -> bool { (*self) == (*other) } + #[inline] + fn ne(&self, other: &$t) -> bool { (*self) != (*other) } + } + )*) + } + + #[stable(feature = "rust1", since = "1.0.0")] + impl PartialEq for () { + #[inline] + fn eq(&self, _other: &()) -> bool { + true + } + #[inline] + fn ne(&self, _other: &()) -> bool { + false + } + } + + partial_eq_impl! { + bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 + } + + macro_rules! eq_impl { + ($($t:ty)*) => ($( + #[stable(feature = "rust1", since = "1.0.0")] + impl Eq for $t {} + )*) + } + + eq_impl! { () bool char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 } + + macro_rules! partial_ord_impl { + ($($t:ty)*) => ($( + #[stable(feature = "rust1", since = "1.0.0")] + impl PartialOrd for $t { + #[inline] + fn partial_cmp(&self, other: &$t) -> Option<Ordering> { + match (self <= other, self >= other) { + (false, false) => None, + (false, true) => Some(Greater), + (true, false) => Some(Less), + (true, true) => Some(Equal), + } + } + #[inline] + fn lt(&self, other: &$t) -> bool { (*self) < (*other) } + #[inline] + fn le(&self, other: &$t) -> bool { (*self) <= (*other) } + #[inline] + fn ge(&self, other: &$t) -> bool { (*self) >= (*other) } + #[inline] + fn gt(&self, other: &$t) -> bool { (*self) > (*other) } + } + )*) + } + + #[stable(feature = "rust1", since = "1.0.0")] + impl PartialOrd for () { + #[inline] + fn partial_cmp(&self, _: &()) -> Option<Ordering> { + Some(Equal) + } + } + + #[stable(feature = "rust1", since = "1.0.0")] + impl PartialOrd for bool { + #[inline] + fn partial_cmp(&self, other: &bool) -> Option<Ordering> { + (*self as u8).partial_cmp(&(*other as u8)) + } + } + + partial_ord_impl! { f32 f64 } + + macro_rules! ord_impl { + ($($t:ty)*) => ($( + #[stable(feature = "rust1", since = "1.0.0")] + impl PartialOrd for $t { + #[inline] + fn partial_cmp(&self, other: &$t) -> Option<Ordering> { + Some(self.cmp(other)) + } + #[inline] + fn lt(&self, other: &$t) -> bool { (*self) < (*other) } + #[inline] + fn le(&self, other: &$t) -> bool { (*self) <= (*other) } + #[inline] + fn ge(&self, other: &$t) -> bool { (*self) >= (*other) } + #[inline] + fn gt(&self, other: &$t) -> bool { (*self) > (*other) } + } + + #[stable(feature = "rust1", since = "1.0.0")] + impl Ord for $t { + #[inline] + fn cmp(&self, other: &$t) -> Ordering { + // The order here is important to generate more optimal assembly. + // See <https://github.com/rust-lang/rust/issues/63758> for more info. + if *self < *other { Less } + else if *self == *other { Equal } + else { Greater } + } + } + )*) + } + + #[stable(feature = "rust1", since = "1.0.0")] + impl Ord for () { + #[inline] + fn cmp(&self, _other: &()) -> Ordering { + Equal + } + } + + #[stable(feature = "rust1", since = "1.0.0")] + impl Ord for bool { + #[inline] + fn cmp(&self, other: &bool) -> Ordering { + // Casting to i8's and converting the difference to an Ordering generates + // more optimal assembly. + // See <https://github.com/rust-lang/rust/issues/66780> for more info. + match (*self as i8) - (*other as i8) { + -1 => Less, + 0 => Equal, + 1 => Greater, + // SAFETY: bool as i8 returns 0 or 1, so the difference can't be anything else + _ => unsafe { unreachable_unchecked() }, + } + } + } + + ord_impl! { char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 } + + #[unstable(feature = "never_type", issue = "35121")] + impl PartialEq for ! { + fn eq(&self, _: &!) -> bool { + *self + } + } + + #[unstable(feature = "never_type", issue = "35121")] + impl Eq for ! {} + + #[unstable(feature = "never_type", issue = "35121")] + impl PartialOrd for ! { + fn partial_cmp(&self, _: &!) -> Option<Ordering> { + *self + } + } + + #[unstable(feature = "never_type", issue = "35121")] + impl Ord for ! { + fn cmp(&self, _: &!) -> Ordering { + *self + } + } + + // & pointers + + #[stable(feature = "rust1", since = "1.0.0")] + impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &A + where + A: PartialEq<B>, + { + #[inline] + fn eq(&self, other: &&B) -> bool { + PartialEq::eq(*self, *other) + } + #[inline] + fn ne(&self, other: &&B) -> bool { + PartialEq::ne(*self, *other) + } + } + #[stable(feature = "rust1", since = "1.0.0")] + impl<A: ?Sized, B: ?Sized> PartialOrd<&B> for &A + where + A: PartialOrd<B>, + { + #[inline] + fn partial_cmp(&self, other: &&B) -> Option<Ordering> { + PartialOrd::partial_cmp(*self, *other) + } + #[inline] + fn lt(&self, other: &&B) -> bool { + PartialOrd::lt(*self, *other) + } + #[inline] + fn le(&self, other: &&B) -> bool { + PartialOrd::le(*self, *other) + } + #[inline] + fn gt(&self, other: &&B) -> bool { + PartialOrd::gt(*self, *other) + } + #[inline] + fn ge(&self, other: &&B) -> bool { + PartialOrd::ge(*self, *other) + } + } + #[stable(feature = "rust1", since = "1.0.0")] + impl<A: ?Sized> Ord for &A + where + A: Ord, + { + #[inline] + fn cmp(&self, other: &Self) -> Ordering { + Ord::cmp(*self, *other) + } + } + #[stable(feature = "rust1", since = "1.0.0")] + impl<A: ?Sized> Eq for &A where A: Eq {} + + // &mut pointers + + #[stable(feature = "rust1", since = "1.0.0")] + impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &mut A + where + A: PartialEq<B>, + { + #[inline] + fn eq(&self, other: &&mut B) -> bool { + PartialEq::eq(*self, *other) + } + #[inline] + fn ne(&self, other: &&mut B) -> bool { + PartialEq::ne(*self, *other) + } + } + #[stable(feature = "rust1", since = "1.0.0")] + impl<A: ?Sized, B: ?Sized> PartialOrd<&mut B> for &mut A + where + A: PartialOrd<B>, + { + #[inline] + fn partial_cmp(&self, other: &&mut B) -> Option<Ordering> { + PartialOrd::partial_cmp(*self, *other) + } + #[inline] + fn lt(&self, other: &&mut B) -> bool { + PartialOrd::lt(*self, *other) + } + #[inline] + fn le(&self, other: &&mut B) -> bool { + PartialOrd::le(*self, *other) + } + #[inline] + fn gt(&self, other: &&mut B) -> bool { + PartialOrd::gt(*self, *other) + } + #[inline] + fn ge(&self, other: &&mut B) -> bool { + PartialOrd::ge(*self, *other) + } + } + #[stable(feature = "rust1", since = "1.0.0")] + impl<A: ?Sized> Ord for &mut A + where + A: Ord, + { + #[inline] + fn cmp(&self, other: &Self) -> Ordering { + Ord::cmp(*self, *other) + } + } + #[stable(feature = "rust1", since = "1.0.0")] + impl<A: ?Sized> Eq for &mut A where A: Eq {} + + #[stable(feature = "rust1", since = "1.0.0")] + impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &A + where + A: PartialEq<B>, + { + #[inline] + fn eq(&self, other: &&mut B) -> bool { + PartialEq::eq(*self, *other) + } + #[inline] + fn ne(&self, other: &&mut B) -> bool { + PartialEq::ne(*self, *other) + } + } + + #[stable(feature = "rust1", since = "1.0.0")] + impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &mut A + where + A: PartialEq<B>, + { + #[inline] + fn eq(&self, other: &&B) -> bool { + PartialEq::eq(*self, *other) + } + #[inline] + fn ne(&self, other: &&B) -> bool { + PartialEq::ne(*self, *other) + } + } +} |