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// Copyright (c) 2011, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
part of dart.core;
/// The signature of a generic comparison function.
/// A comparison function represents an ordering on a type of objects.
/// A total ordering on a type means that for two values, either they
/// are equal or one is greater than the other (and the latter must then be
/// smaller than the former).
/// A [Comparator] function represents such a total ordering by returning
/// * a negative integer if [a] is smaller than [b],
/// * zero if [a] is equal to [b], and
/// * a positive integer if [a] is greater than [b].
typedef Comparator<T> = int Function(T a, T b);
/// Interface used by types that have an intrinsic ordering.
/// The [compareTo] operation defines a total ordering of objects,
/// which can be used for ordering and sorting.
/// The [Comparable] interface should be used for the natural ordering of a type.
/// If a type can be ordered in more than one way,
/// and none of them is the obvious natural ordering,
/// then it might be better not to use the [Comparable] interface,
/// and to provide separate [Comparator]s instead.
/// It is recommended that the order of a [Comparable] agrees
/// with its operator [operator ==] equality (`a.compareTo(b) == 0` iff `a == b`),
/// but this is not a requirement.
/// For example, [double] and [DateTime] have `compareTo` methods
/// that do not agree with operator [operator ==].
/// For doubles the [compareTo] method is more precise than the equality,
/// and for [DateTime] it is less precise.
/// Examples:
/// ```dart
/// (0.0).compareTo(-0.0); // => 1
/// 0.0 == -0.0; // => true
/// var now =;
/// var utcNow = now.toUtc();
/// now == utcNow; // => false
/// now.compareTo(utcNow); // => 0
/// ```
/// The [Comparable] interface does not imply the existence
/// of the comparison operators `<`, `<=`, `>` and `>=`.
/// These should only be defined
/// if the ordering is a less-than/greater-than ordering,
/// that is, an ordering where you would naturally
/// use the words "less than" about the order of two elements.
/// If the equality operator and [compareTo] disagree,
/// the comparison operators should follow the equality operator,
/// and will likely also disagree with [compareTo].
/// Otherwise they should match the [compareTo] method,
/// so that `a < b` iff `a.compareTo(b) < 0`.
/// The [double] class defines comparison operators
/// that are compatible with equality.
/// The operators differ from [double.compareTo] on -0.0 and NaN.
/// The [DateTime] class has no comparison operators, instead it has the more
/// precisely named [DateTime.isBefore] and [DateTime.isAfter], which both
/// agree with [DateTime.compareTo].
abstract class Comparable<T> {
/// Compares this object to another object.
/// Returns a value like a [Comparator] when comparing `this` to [other].
/// That is, it returns a negative integer if `this` is ordered before [other],
/// a positive integer if `this` is ordered after [other],
/// and zero if `this` and [other] are ordered together.
/// The [other] argument must be a value that is comparable to this object.
int compareTo(T other);
/// A [Comparator] that compares one comparable to another.
/// It returns the result of `a.compareTo(b)`.
/// The call may fail at run-time
/// if `a` is not comparable to the type of `b`.
/// This utility function is used as the default comparator
/// for ordering collections, for example in the [List] sort function.
static int compare(Comparable a, Comparable b) => a.compareTo(b);