| //! Utilities for comparing and ordering values. |
| //! |
| //! This module contains various tools for comparing and ordering values. In |
| //! summary: |
| //! |
| //! * [`PartialEq<Rhs>`] overloads the `==` and `!=` operators. In cases where |
| //! `Rhs` (the right hand side's type) is `Self`, this trait corresponds to a |
| //! partial equivalence relation. |
| //! * [`Eq`] indicates that the overloaded `==` operator corresponds to an |
| //! equivalence relation. |
| //! * [`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 of two values (less, equal, or |
| //! greater). |
| //! * [`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. |
| //! |
| //! [`max`]: Ord::max |
| //! [`min`]: Ord::min |
| |
| #![stable(feature = "rust1", since = "1.0.0")] |
| |
| mod bytewise; |
| pub(crate) use bytewise::BytewiseEq; |
| |
| use self::Ordering::*; |
| |
| /// Trait for comparisons using the equality operator. |
| /// |
| /// Implementing this trait for types provides the `==` and `!=` operators for |
| /// those types. |
| /// |
| /// `x.eq(y)` can also be written `x == y`, and `x.ne(y)` can be written `x != y`. |
| /// We use the easier-to-read infix notation in the remainder of this documentation. |
| /// |
| /// This trait allows for comparisons using the equality operator, 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 |
| /// [`trait@Eq`]. Formally speaking, when `Rhs == Self`, this trait corresponds |
| /// to a [partial equivalence relation]. |
| /// |
| /// [partial equivalence relation]: https://en.wikipedia.org/wiki/Partial_equivalence_relation |
| /// |
| /// Implementations must ensure that `eq` and `ne` are consistent with each other: |
| /// |
| /// - `a != b` if and only if `!(a == b)`. |
| /// |
| /// The default implementation of `ne` provides this consistency and is almost |
| /// always sufficient. It should not be overridden without very good reason. |
| /// |
| /// If [`PartialOrd`] or [`Ord`] are also implemented for `Self` and `Rhs`, their methods must also |
| /// be consistent with `PartialEq` (see the documentation of those traits for the exact |
| /// requirements). It's easy to accidentally make them disagree by deriving some of the traits and |
| /// manually implementing others. |
| /// |
| /// The equality relation `==` must satisfy the following conditions |
| /// (for all `a`, `b`, `c` of type `A`, `B`, `C`): |
| /// |
| /// - **Symmetric**: if `A: PartialEq<B>` and `B: PartialEq<A>`, then **`a == b` |
| /// implies `b == a`**; and |
| /// |
| /// - **Transitive**: if `A: PartialEq<B>` and `B: PartialEq<C>` and `A: |
| /// PartialEq<C>`, then **`a == b` and `b == c` implies `a == c`**. |
| /// |
| /// Note that the `B: PartialEq<A>` (symmetric) and `A: PartialEq<C>` |
| /// (transitive) impls are not forced to exist, but these requirements apply |
| /// whenever they do exist. |
| /// |
| /// Violating these requirements is a logic error. The behavior resulting from a logic error is not |
| /// specified, but users of the trait must ensure that such logic errors do *not* result in |
| /// undefined behavior. This means that `unsafe` code **must not** rely on the correctness of these |
| /// methods. |
| /// |
| /// ## 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, two instances are equal if they |
| /// are the same variant and all fields are equal. |
| /// |
| /// ## How can I implement `PartialEq`? |
| /// |
| /// 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}`", |
| append_const_msg |
| )] |
| #[rustc_diagnostic_item = "PartialEq"] |
| #[const_trait] |
| 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")] |
| #[rustc_diagnostic_item = "cmp_partialeq_eq"] |
| fn eq(&self, other: &Rhs) -> bool; |
| |
| /// This method tests for `!=`. The default implementation is almost always |
| /// sufficient, and should not be overridden without very good reason. |
| #[inline] |
| #[must_use] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[rustc_diagnostic_item = "cmp_partialeq_ne"] |
| fn ne(&self, other: &Rhs) -> bool { |
| !self.eq(other) |
| } |
| } |
| |
| /// Derive macro generating an impl of the trait [`PartialEq`]. |
| /// The behavior of this macro is described in detail [here](PartialEq#derivable). |
| #[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 comparisons corresponding to [equivalence relations]( |
| /// https://en.wikipedia.org/wiki/Equivalence_relation). |
| /// |
| /// This means, that in addition to `a == b` and `a != b` being strict inverses, |
| /// the relation must be (for all `a`, `b` and `c`): |
| /// |
| /// - reflexive: `a == a`; |
| /// - symmetric: `a == b` implies `b == a` (required by `PartialEq` as well); and |
| /// - transitive: `a == b` and `b == c` implies `a == c` (required by `PartialEq` as well). |
| /// |
| /// This property cannot be checked by the compiler, and therefore `Eq` implies |
| /// [`PartialEq`], and has no extra methods. |
| /// |
| /// Violating this property is a logic error. The behavior resulting from a logic error is not |
| /// specified, but users of the trait must ensure that such logic errors do *not* result in |
| /// undefined behavior. This means that `unsafe` code **must not** rely on the correctness of these |
| /// methods. |
| /// |
| /// Implement `Eq` in addition to `PartialEq` if it's guaranteed that |
| /// `PartialEq::eq(a, a)` always returns `true` (reflexivity), in addition to |
| /// the symmetric and transitive properties already required by `PartialEq`. |
| /// |
| /// ## 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")] |
| #[rustc_diagnostic_item = "Eq"] |
| pub trait Eq: PartialEq<Self> { |
| // this method is used solely by #[derive(Eq)] to assert |
| // that every component of a type implements `Eq` |
| // 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)] |
| #[coverage(off)] |
| #[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)] |
| #[allow_internal_unstable(coverage_attribute)] |
| 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; |
| /// |
| /// assert_eq!(1.cmp(&2), Ordering::Less); |
| /// |
| /// assert_eq!(1.cmp(&1), Ordering::Equal); |
| /// |
| /// assert_eq!(2.cmp(&1), Ordering::Greater); |
| /// ``` |
| #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[repr(i8)] |
| 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 { |
| /// Returns `true` if the ordering is the `Equal` variant. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cmp::Ordering; |
| /// |
| /// assert_eq!(Ordering::Less.is_eq(), false); |
| /// assert_eq!(Ordering::Equal.is_eq(), true); |
| /// assert_eq!(Ordering::Greater.is_eq(), false); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")] |
| #[stable(feature = "ordering_helpers", since = "1.53.0")] |
| pub const fn is_eq(self) -> bool { |
| matches!(self, Equal) |
| } |
| |
| /// Returns `true` if the ordering is not the `Equal` variant. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cmp::Ordering; |
| /// |
| /// assert_eq!(Ordering::Less.is_ne(), true); |
| /// assert_eq!(Ordering::Equal.is_ne(), false); |
| /// assert_eq!(Ordering::Greater.is_ne(), true); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")] |
| #[stable(feature = "ordering_helpers", since = "1.53.0")] |
| pub const fn is_ne(self) -> bool { |
| !matches!(self, Equal) |
| } |
| |
| /// Returns `true` if the ordering is the `Less` variant. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cmp::Ordering; |
| /// |
| /// assert_eq!(Ordering::Less.is_lt(), true); |
| /// assert_eq!(Ordering::Equal.is_lt(), false); |
| /// assert_eq!(Ordering::Greater.is_lt(), false); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")] |
| #[stable(feature = "ordering_helpers", since = "1.53.0")] |
| pub const fn is_lt(self) -> bool { |
| matches!(self, Less) |
| } |
| |
| /// Returns `true` if the ordering is the `Greater` variant. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cmp::Ordering; |
| /// |
| /// assert_eq!(Ordering::Less.is_gt(), false); |
| /// assert_eq!(Ordering::Equal.is_gt(), false); |
| /// assert_eq!(Ordering::Greater.is_gt(), true); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")] |
| #[stable(feature = "ordering_helpers", since = "1.53.0")] |
| pub const fn is_gt(self) -> bool { |
| matches!(self, Greater) |
| } |
| |
| /// Returns `true` if the ordering is either the `Less` or `Equal` variant. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cmp::Ordering; |
| /// |
| /// assert_eq!(Ordering::Less.is_le(), true); |
| /// assert_eq!(Ordering::Equal.is_le(), true); |
| /// assert_eq!(Ordering::Greater.is_le(), false); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")] |
| #[stable(feature = "ordering_helpers", since = "1.53.0")] |
| pub const fn is_le(self) -> bool { |
| !matches!(self, Greater) |
| } |
| |
| /// Returns `true` if the ordering is either the `Greater` or `Equal` variant. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::cmp::Ordering; |
| /// |
| /// assert_eq!(Ordering::Less.is_ge(), false); |
| /// assert_eq!(Ordering::Equal.is_ge(), true); |
| /// assert_eq!(Ordering::Greater.is_ge(), true); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[rustc_const_stable(feature = "ordering_helpers", since = "1.53.0")] |
| #[stable(feature = "ordering_helpers", since = "1.53.0")] |
| pub const fn is_ge(self) -> bool { |
| !matches!(self, Less) |
| } |
| |
| /// 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] |
| #[rustc_const_stable(feature = "const_ordering", since = "1.48.0")] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub const 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] |
| #[rustc_const_stable(feature = "const_ordering", since = "1.48.0")] |
| #[stable(feature = "ordering_chaining", since = "1.17.0")] |
| pub const 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, Default, Hash)] |
| #[stable(feature = "reverse_cmp_key", since = "1.19.0")] |
| #[repr(transparent)] |
| 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) |
| } |
| } |
| |
| #[stable(feature = "reverse_cmp_key", since = "1.19.0")] |
| impl<T: Clone> Clone for Reverse<T> { |
| #[inline] |
| fn clone(&self) -> Reverse<T> { |
| Reverse(self.0.clone()) |
| } |
| |
| #[inline] |
| fn clone_from(&mut self, other: &Self) { |
| self.0.clone_from(&other.0) |
| } |
| } |
| |
| /// Trait for types that form a [total order](https://en.wikipedia.org/wiki/Total_order). |
| /// |
| /// Implementations must be consistent with the [`PartialOrd`] implementation, and ensure |
| /// `max`, `min`, and `clamp` are consistent with `cmp`: |
| /// |
| /// - `partial_cmp(a, b) == Some(cmp(a, b))`. |
| /// - `max(a, b) == max_by(a, b, cmp)` (ensured by the default implementation). |
| /// - `min(a, b) == min_by(a, b, cmp)` (ensured by the default implementation). |
| /// - For `a.clamp(min, max)`, see the [method docs](#method.clamp) |
| /// (ensured by the default implementation). |
| /// |
| /// It's easy to accidentally make `cmp` and `partial_cmp` disagree by |
| /// deriving some of the traits and manually implementing others. |
| /// |
| /// Violating these requirements is a logic error. The behavior resulting from a logic error is not |
| /// specified, but users of the trait must ensure that such logic errors do *not* result in |
| /// undefined behavior. This means that `unsafe` code **must not** rely on the correctness of these |
| /// methods. |
| /// |
| /// ## Corollaries |
| /// |
| /// From the above and the requirements of `PartialOrd`, it follows that for |
| /// all `a`, `b` and `c`: |
| /// |
| /// - exactly one of `a < b`, `a == b` or `a > b` is true; and |
| /// - `<` is transitive: `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`. |
| /// |
| /// Mathematically speaking, the `<` operator defines a strict [weak order]. In |
| /// cases where `==` conforms to mathematical equality, it also defines a |
| /// strict [total order]. |
| /// |
| /// [weak order]: https://en.wikipedia.org/wiki/Weak_ordering |
| /// [total order]: https://en.wikipedia.org/wiki/Total_order |
| /// |
| /// ## Derivable |
| /// |
| /// This trait can be used with `#[derive]`. |
| /// |
| /// When `derive`d on structs, it will produce a |
| /// [lexicographic](https://en.wikipedia.org/wiki/Lexicographic_order) ordering |
| /// based on the top-to-bottom declaration order of the struct's members. |
| /// |
| /// When `derive`d on enums, variants are ordered primarily by their discriminants. |
| /// Secondarily, they are ordered by their fields. |
| /// By default, the discriminant is smallest for variants at the top, and |
| /// largest for variants at the bottom. Here's an example: |
| /// |
| /// ``` |
| /// #[derive(PartialEq, Eq, PartialOrd, Ord)] |
| /// enum E { |
| /// Top, |
| /// Bottom, |
| /// } |
| /// |
| /// assert!(E::Top < E::Bottom); |
| /// ``` |
| /// |
| /// However, manually setting the discriminants can override this default |
| /// behavior: |
| /// |
| /// ``` |
| /// #[derive(PartialEq, Eq, PartialOrd, Ord)] |
| /// enum E { |
| /// Top = 2, |
| /// Bottom = 1, |
| /// } |
| /// |
| /// assert!(E::Bottom < E::Top); |
| /// ``` |
| /// |
| /// ## Lexicographical comparison |
| /// |
| /// Lexicographical comparison is an operation with the following properties: |
| /// - Two sequences are compared element by element. |
| /// - The first mismatching element defines which sequence is lexicographically less or greater than the other. |
| /// - If one sequence is a prefix of another, the shorter sequence is lexicographically less than the other. |
| /// - If two sequences have equivalent elements and are of the same length, then the sequences are lexicographically equal. |
| /// - An empty sequence is lexicographically less than any non-empty sequence. |
| /// - Two empty sequences are lexicographically equal. |
| /// |
| /// ## 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. |
| /// |
| /// 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")] |
| #[rustc_diagnostic_item = "Ord"] |
| 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")] |
| #[rustc_diagnostic_item = "ord_cmp_method"] |
| 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!(1.max(2), 2); |
| /// assert_eq!(2.max(2), 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.min(2), 1); |
| /// assert_eq!(2.min(2), 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 |
| /// |
| /// ``` |
| /// assert_eq!((-3).clamp(-2, 1), -2); |
| /// assert_eq!(0.clamp(-2, 1), 0); |
| /// assert_eq!(2.clamp(-2, 1), 1); |
| /// ``` |
| #[must_use] |
| #[stable(feature = "clamp", since = "1.50.0")] |
| fn clamp(self, min: Self, max: Self) -> Self |
| where |
| Self: Sized, |
| Self: PartialOrd, |
| { |
| assert!(min <= max); |
| if self < min { |
| min |
| } else if self > max { |
| max |
| } else { |
| self |
| } |
| } |
| } |
| |
| /// Derive macro generating an impl of the trait [`Ord`]. |
| /// The behavior of this macro is described in detail [here](Ord#derivable). |
| #[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 */ |
| } |
| |
| /// Trait for types that form a [partial order](https://en.wikipedia.org/wiki/Partial_order). |
| /// |
| /// The `lt`, `le`, `gt`, and `ge` methods of this trait can be called using |
| /// the `<`, `<=`, `>`, and `>=` operators, respectively. |
| /// |
| /// The methods of this trait must be consistent with each other and with those of [`PartialEq`]. |
| /// The following conditions must hold: |
| /// |
| /// 1. `a == b` if and only if `partial_cmp(a, b) == Some(Equal)`. |
| /// 2. `a < b` if and only if `partial_cmp(a, b) == Some(Less)` |
| /// 3. `a > b` if and only if `partial_cmp(a, b) == Some(Greater)` |
| /// 4. `a <= b` if and only if `a < b || a == b` |
| /// 5. `a >= b` if and only if `a > b || a == b` |
| /// 6. `a != b` if and only if `!(a == b)`. |
| /// |
| /// Conditions 2–5 above are ensured by the default implementation. |
| /// Condition 6 is already ensured by [`PartialEq`]. |
| /// |
| /// If [`Ord`] is also implemented for `Self` and `Rhs`, it must also be consistent with |
| /// `partial_cmp` (see the documentation of that trait for the exact requirements). It's |
| /// easy to accidentally make them disagree by deriving some of the traits and manually |
| /// implementing others. |
| /// |
| /// The comparison must satisfy, for all `a`, `b` and `c`: |
| /// |
| /// - transitivity: `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`. |
| /// - duality: `a < b` if and only if `b > a`. |
| /// |
| /// 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>`. |
| /// |
| /// Violating these requirements is a logic error. The behavior resulting from a logic error is not |
| /// specified, but users of the trait must ensure that such logic errors do *not* result in |
| /// undefined behavior. This means that `unsafe` code **must not** rely on the correctness of these |
| /// methods. |
| /// |
| /// ## Corollaries |
| /// |
| /// The following corollaries follow from the above requirements: |
| /// |
| /// - irreflexivity of `<` and `>`: `!(a < a)`, `!(a > a)` |
| /// - transitivity of `>`: if `a > b` and `b > c` then `a > c` |
| /// - duality of `partial_cmp`: `partial_cmp(a, b) == partial_cmp(b, a).map(Ordering::reverse)` |
| /// |
| /// ## Strict and non-strict partial orders |
| /// |
| /// The `<` and `>` operators behave according to a *strict* partial order. |
| /// However, `<=` and `>=` do **not** behave according to a *non-strict* |
| /// partial order. |
| /// That is because mathematically, a non-strict partial order would require |
| /// reflexivity, i.e. `a <= a` would need to be true for every `a`. This isn't |
| /// always the case for types that implement `PartialOrd`, for example: |
| /// |
| /// ``` |
| /// let a = f64::sqrt(-1.0); |
| /// assert_eq!(a <= a, false); |
| /// ``` |
| /// |
| /// ## Derivable |
| /// |
| /// This trait can be used with `#[derive]`. |
| /// |
| /// When `derive`d on structs, it will produce a |
| /// [lexicographic](https://en.wikipedia.org/wiki/Lexicographic_order) ordering |
| /// based on the top-to-bottom declaration order of the struct's members. |
| /// |
| /// When `derive`d on enums, variants are primarily ordered by their discriminants. |
| /// Secondarily, they are ordered by their fields. |
| /// By default, the discriminant is smallest for variants at the top, and |
| /// largest for variants at the bottom. Here's an example: |
| /// |
| /// ``` |
| /// #[derive(PartialEq, PartialOrd)] |
| /// enum E { |
| /// Top, |
| /// Bottom, |
| /// } |
| /// |
| /// assert!(E::Top < E::Bottom); |
| /// ``` |
| /// |
| /// However, manually setting the discriminants can override this default |
| /// behavior: |
| /// |
| /// ``` |
| /// #[derive(PartialEq, PartialOrd)] |
| /// enum E { |
| /// Top = 2, |
| /// Bottom = 1, |
| /// } |
| /// |
| /// assert!(E::Bottom < E::Top); |
| /// ``` |
| /// |
| /// ## 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`]. |
| /// |
| /// 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: &Self) -> Option<Ordering> { |
| /// Some(self.cmp(other)) |
| /// } |
| /// } |
| /// |
| /// impl Ord for Person { |
| /// fn cmp(&self, other: &Self) -> Ordering { |
| /// self.height.cmp(&other.height) |
| /// } |
| /// } |
| /// |
| /// impl PartialEq for Person { |
| /// fn eq(&self, other: &Self) -> 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}`", |
| append_const_msg |
| )] |
| #[rustc_diagnostic_item = "PartialOrd"] |
| 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 |
| /// |
| /// ``` |
| /// assert_eq!(1.0 < 1.0, false); |
| /// assert_eq!(1.0 < 2.0, true); |
| /// assert_eq!(2.0 < 1.0, 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 |
| /// |
| /// ``` |
| /// assert_eq!(1.0 <= 1.0, true); |
| /// assert_eq!(1.0 <= 2.0, true); |
| /// assert_eq!(2.0 <= 1.0, false); |
| /// ``` |
| #[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 |
| /// |
| /// ``` |
| /// assert_eq!(1.0 > 1.0, false); |
| /// assert_eq!(1.0 > 2.0, false); |
| /// assert_eq!(2.0 > 1.0, true); |
| /// ``` |
| #[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 |
| /// |
| /// ``` |
| /// assert_eq!(1.0 >= 1.0, true); |
| /// assert_eq!(1.0 >= 2.0, false); |
| /// assert_eq!(2.0 >= 1.0, 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`]. |
| /// The behavior of this macro is described in detail [here](PartialOrd#derivable). |
| #[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!(cmp::min(1, 2), 1); |
| /// assert_eq!(cmp::min(2, 2), 2); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[cfg_attr(not(test), rustc_diagnostic_item = "cmp_min")] |
| 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 |
| /// |
| /// ``` |
| /// use std::cmp; |
| /// |
| /// let result = cmp::min_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())); |
| /// assert_eq!(result, 1); |
| /// |
| /// let result = cmp::min_by(-2, 3, |x: &i32, y: &i32| x.abs().cmp(&y.abs())); |
| /// assert_eq!(result, -2); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[stable(feature = "cmp_min_max_by", since = "1.53.0")] |
| 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 |
| /// |
| /// ``` |
| /// use std::cmp; |
| /// |
| /// let result = cmp::min_by_key(-2, 1, |x: &i32| x.abs()); |
| /// assert_eq!(result, 1); |
| /// |
| /// let result = cmp::min_by_key(-2, 2, |x: &i32| x.abs()); |
| /// assert_eq!(result, -2); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[stable(feature = "cmp_min_max_by", since = "1.53.0")] |
| 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!(cmp::max(1, 2), 2); |
| /// assert_eq!(cmp::max(2, 2), 2); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[cfg_attr(not(test), rustc_diagnostic_item = "cmp_max")] |
| 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 |
| /// |
| /// ``` |
| /// use std::cmp; |
| /// |
| /// let result = cmp::max_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())); |
| /// assert_eq!(result, -2); |
| /// |
| /// let result = cmp::max_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())) ; |
| /// assert_eq!(result, 2); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[stable(feature = "cmp_min_max_by", since = "1.53.0")] |
| 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 |
| /// |
| /// ``` |
| /// use std::cmp; |
| /// |
| /// let result = cmp::max_by_key(-2, 1, |x: &i32| x.abs()); |
| /// assert_eq!(result, -2); |
| /// |
| /// let result = cmp::max_by_key(-2, 2, |x: &i32| x.abs()); |
| /// assert_eq!(result, 2); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[stable(feature = "cmp_min_max_by", since = "1.53.0")] |
| 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))) |
| } |
| |
| /// Compares and sorts two values, returning minimum and maximum. |
| /// |
| /// Returns `[v1, v2]` if the comparison determines them to be equal. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(cmp_minmax)] |
| /// use std::cmp; |
| /// |
| /// assert_eq!(cmp::minmax(1, 2), [1, 2]); |
| /// assert_eq!(cmp::minmax(2, 2), [2, 2]); |
| /// |
| /// // You can destructure the result using array patterns |
| /// let [min, max] = cmp::minmax(42, 17); |
| /// assert_eq!(min, 17); |
| /// assert_eq!(max, 42); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[unstable(feature = "cmp_minmax", issue = "115939")] |
| pub fn minmax<T>(v1: T, v2: T) -> [T; 2] |
| where |
| T: Ord, |
| { |
| if v1 <= v2 { [v1, v2] } else { [v2, v1] } |
| } |
| |
| /// Returns minimum and maximum values with respect to the specified comparison function. |
| /// |
| /// Returns `[v1, v2]` if the comparison determines them to be equal. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(cmp_minmax)] |
| /// use std::cmp; |
| /// |
| /// assert_eq!(cmp::minmax_by(-2, 1, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), [1, -2]); |
| /// assert_eq!(cmp::minmax_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), [-2, 2]); |
| /// |
| /// // You can destructure the result using array patterns |
| /// let [min, max] = cmp::minmax_by(-42, 17, |x: &i32, y: &i32| x.abs().cmp(&y.abs())); |
| /// assert_eq!(min, 17); |
| /// assert_eq!(max, -42); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[unstable(feature = "cmp_minmax", issue = "115939")] |
| pub fn minmax_by<T, F>(v1: T, v2: T, compare: F) -> [T; 2] |
| where |
| F: FnOnce(&T, &T) -> Ordering, |
| { |
| if compare(&v1, &v2).is_le() { [v1, v2] } else { [v2, v1] } |
| } |
| |
| /// Returns minimum and maximum values with respect to the specified key function. |
| /// |
| /// Returns `[v1, v2]` if the comparison determines them to be equal. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(cmp_minmax)] |
| /// use std::cmp; |
| /// |
| /// assert_eq!(cmp::minmax_by_key(-2, 1, |x: &i32| x.abs()), [1, -2]); |
| /// assert_eq!(cmp::minmax_by_key(-2, 2, |x: &i32| x.abs()), [-2, 2]); |
| /// |
| /// // You can destructure the result using array patterns |
| /// let [min, max] = cmp::minmax_by_key(-42, 17, |x: &i32| x.abs()); |
| /// assert_eq!(min, 17); |
| /// assert_eq!(max, -42); |
| /// ``` |
| #[inline] |
| #[must_use] |
| #[unstable(feature = "cmp_minmax", issue = "115939")] |
| pub fn minmax_by_key<T, F, K>(v1: T, v2: T, mut f: F) -> [T; 2] |
| where |
| F: FnMut(&T) -> K, |
| K: Ord, |
| { |
| minmax_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")] |
| #[rustc_const_unstable(feature = "const_cmp", issue = "92391")] |
| impl const 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(always)] |
| fn lt(&self, other: &$t) -> bool { (*self) < (*other) } |
| #[inline(always)] |
| fn le(&self, other: &$t) -> bool { (*self) <= (*other) } |
| #[inline(always)] |
| fn ge(&self, other: &$t) -> bool { (*self) >= (*other) } |
| #[inline(always)] |
| fn gt(&self, other: &$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> { |
| Some(self.cmp(other)) |
| } |
| } |
| |
| 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(always)] |
| fn lt(&self, other: &$t) -> bool { (*self) < (*other) } |
| #[inline(always)] |
| fn le(&self, other: &$t) -> bool { (*self) <= (*other) } |
| #[inline(always)] |
| fn ge(&self, other: &$t) -> bool { (*self) >= (*other) } |
| #[inline(always)] |
| fn gt(&self, other: &$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() }, |
| } |
| } |
| |
| #[inline] |
| fn min(self, other: bool) -> bool { |
| self & other |
| } |
| |
| #[inline] |
| fn max(self, other: bool) -> bool { |
| self | other |
| } |
| |
| #[inline] |
| fn clamp(self, min: bool, max: bool) -> bool { |
| assert!(min <= max); |
| self.max(min).min(max) |
| } |
| } |
| |
| ord_impl! { char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 } |
| |
| #[unstable(feature = "never_type", issue = "35121")] |
| impl PartialEq for ! { |
| #[inline] |
| fn eq(&self, _: &!) -> bool { |
| *self |
| } |
| } |
| |
| #[unstable(feature = "never_type", issue = "35121")] |
| impl Eq for ! {} |
| |
| #[unstable(feature = "never_type", issue = "35121")] |
| impl PartialOrd for ! { |
| #[inline] |
| fn partial_cmp(&self, _: &!) -> Option<Ordering> { |
| *self |
| } |
| } |
| |
| #[unstable(feature = "never_type", issue = "35121")] |
| impl Ord for ! { |
| #[inline] |
| 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) |
| } |
| } |
| } |