blob: 835aa34b1f6a8286364ef928b712b7044aa226f4 [file] [log] [blame]
// 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:
* (0.0).compareTo(-0.0); // => 1
* 0.0 == -0.0; // => true
* var dt = new;
* var dt2 = dt.toUtc();
* dt == dt2; // => false
* dt.compareTo(dt2); // => 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].
abstract class Comparable<T> {
* Compares this object to another [Comparable]
* 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)`.
* 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);