// Copyright (c) 2013, 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:collection"; /// An insertion-ordered [Map] with expected constant-time lookup. /// /// A non-constant map literal, like `{"a": 42, "b": 7}`, is a `LinkedHashMap`. /// /// The [keys], [values] and [entries] are iterated in key insertion order. /// /// The map uses a hash-table to look up entries, so keys must have /// suitable implementations of [Object.operator==] and [Object.hashCode]. /// If the hash codes are not well-distributed, the performance of map /// operations may suffer. /// /// The insertion order of keys is remembered, /// and keys are iterated in the order they were inserted into the map. /// Values and entries are iterated in their corresponding key's order. /// Changing a key's value, when the key is already in the map, /// does not change the iteration order, /// but removing the key and adding it again /// will make it be last in the iteration order. /// /// **Notice:** /// Do not modify a map (add or remove keys) while an operation /// is being performed on that map, for example in functions /// called during a [forEach] or [putIfAbsent] call, /// or while iterating the map ([keys], [values] or [entries]). /// /// The keys of a `LinkedHashMap` must have consistent [Object.==] /// and [Object.hashCode] implementations. This means that the `==` operator /// must define a stable equivalence relation on the keys (reflexive, /// symmetric, transitive, and consistent over time), and that `hashCode` /// must be the same for objects that are considered equal by `==`. /// /// Example: /// /// ```dart /// final planetsByDiameter = {0.949: 'Venus'}; // A new LinkedHashMap /// ``` /// To add data to a map, use [operator[]=], [addAll] or [addEntries]. /// ```dart continued /// planetsByDiameter[1] = 'Earth'; /// planetsByDiameter.addAll({0.532: 'Mars', 11.209: 'Jupiter'}); /// ``` /// To check if the map is empty, use [isEmpty] or [isNotEmpty]. /// To find the number of map entries, use [length]. /// ```dart continued /// print(planetsByDiameter.isEmpty); // false /// print(planetsByDiameter.length); // 4 /// print(planetsByDiameter); /// // {0.949: Venus, 1.0: Earth, 0.532: Mars, 11.209: Jupiter} /// ``` /// The [forEach] method calls a function for each key/value entry of the map. /// ```dart continued /// planetsByDiameter.forEach((key, value) { /// print('$key \t $value'); /// // 0.949 Venus /// // 1.0 Earth /// // 0.532 Mars /// // 11.209 Jupiter /// }); /// ``` /// To check whether the map has an entry with a specific key, use [containsKey]. /// ```dart continued /// final keyOneExists = planetsByDiameter.containsKey(1); // true /// final keyFiveExists = planetsByDiameter.containsKey(5); // false /// ``` /// To check whether the map has an entry with a specific value, /// use [containsValue]. /// ```dart continued /// final earthExists = planetsByDiameter.containsValue('Earth'); // true /// final saturnExists = planetsByDiameter.containsValue('Saturn'); // false /// ``` /// To remove an entry with a specific key, use [remove]. /// ```dart continued /// final removedValue = planetsByDiameter.remove(1); /// print(removedValue); // Earth /// print(planetsByDiameter); // {0.949: Venus, 0.532: Mars, 11.209: Jupiter} /// ``` /// To remove multiple entries at the same time, based on their keys and values, /// use [removeWhere]. /// ```dart continued /// planetsByDiameter.removeWhere((key, value) => key == 0.949); /// print(planetsByDiameter); // {0.532: Mars, 11.209: Jupiter} /// ``` /// To conditionally add or modify a value for a specific key, depending on /// whether there already is an entry with that key, /// use [putIfAbsent] or [update]. /// ```dart continued /// planetsByDiameter.update(0.949, (v) => 'Venus', ifAbsent: () => 'Venus'); /// planetsByDiameter.putIfAbsent(0.532, () => "Another Mars if needed"); /// print(planetsByDiameter); // {0.532: Mars, 11.209: Jupiter, 0.949: Venus} /// ``` /// To update the values of all keys, based on the existing key and value, /// use [updateAll]. /// ```dart continued /// planetsByDiameter.updateAll((key, value) => 'X'); /// print(planetsByDiameter); // {0.532: X, 11.209: X, 0.949: X} /// ``` /// To remove all entries and empty the map, use [clear]. /// ```dart continued /// planetsByDiameter.clear(); /// print(planetsByDiameter); // {} /// print(planetsByDiameter.isEmpty); // true /// ``` /// **See also:** /// * [Map], the general interface of key/value pair collections. /// * [HashMap] is unordered (the order of iteration is not guaranteed). /// * [SplayTreeMap] iterates the keys in sorted order. abstract final class LinkedHashMap implements Map { /// Creates an insertion-ordered hash-table based [Map]. /// /// If [equals] is provided, it is used to compare the keys in the table with /// new keys. If [equals] is omitted, the key's own [Object.==] is used /// instead. /// The [equals] function *must not* change the map it's used as an equality /// for. If it does, the resulting behavior is unspecified. /// /// Similarly, if [hashCode] is provided, it is used to produce a hash value /// for keys in order to place them in the hash table. If it is omitted, the /// key's own [Object.hashCode] is used. /// The [hashCode] function *must not* change the map it's used as a hash code /// for. If it does, the resulting behavior is unspecified. /// /// The used `equals` and `hashCode` methods should always be consistent, /// so that if `equals(a, b)` then `hashCode(a) == hashCode(b)`. The hash /// of an object, or what it compares equal to, should not change while the /// object is in the table. If the hash code or equality of an object does /// change, the resulting behavior is unspecified. /// /// If you supply one of [equals] or [hashCode], /// you should generally also supply the other. /// /// Some [equals] or [hashCode] functions might not work for all objects. /// If [isValidKey] is supplied, it's used to check a potential key /// which is not necessarily an instance of [K], like the arguments to /// [operator []], [remove] and [containsKey], which are typed as `Object?`. /// If [isValidKey] returns `false`, for an object, the [equals] and /// [hashCode] functions are not called, and no key equal to that object /// is assumed to be in the map. /// The [isValidKey] function defaults to just testing if the object is an /// instance of [K]. /// /// Example: /// ```dart template:expression /// LikedHashMap(equals: (int a, int b) => (b - a) % 5 == 0, /// hashCode: (int e) => e % 5) /// ``` /// This example map does not need an `isValidKey` function to be passed. /// The default function accepts precisely `int` values, which can safely be /// passed to both the `equals` and `hashCode` functions. /// /// If neither `equals`, `hashCode`, nor `isValidKey` is provided, /// the default `isValidKey` instead accepts all keys. /// The default equality and hashcode operations are assumed to work on all /// objects. /// /// Likewise, if `equals` is [identical], `hashCode` is [identityHashCode] /// and `isValidKey` is omitted, the resulting map is identity based, /// and the `isValidKey` defaults to accepting all keys. /// Such a map can be created directly using [LinkedHashMap.identity]. external factory LinkedHashMap({ bool Function(K, K)? equals, int Function(K)? hashCode, bool Function(dynamic)? isValidKey, }); /// Creates an insertion-ordered identity-based map. /// /// Effectively shorthand for: /// ```dart template:expression /// LinkedHashMap(equals: identical, /// hashCode: identityHashCode) /// ``` external factory LinkedHashMap.identity(); /// Creates a [LinkedHashMap] that contains all key value pairs of [other]. /// /// The keys must all be instances of [K] and the values to [V]. /// The [other] map itself can have any type. /// Example: /// ```dart /// final baseMap = {1: 'A', 2: 'B', 3: 'C'}; /// final fromBaseMap = LinkedHashMap.from(baseMap); /// print(fromBaseMap); // {1: A, 2: B, 3: C} /// ``` factory LinkedHashMap.from(Map other) { LinkedHashMap result = LinkedHashMap(); other.forEach((dynamic k, dynamic v) { result[k as K] = v as V; }); return result; } /// Creates a [LinkedHashMap] that contains all key value pairs of [other]. /// Example: /// ```dart /// final baseMap = {3: 'A', 2: 'B', 1: 'C', 4: 'D'}; /// final mapOf = LinkedHashMap.of(baseMap); /// print(mapOf); // {3: A, 2: B, 1: C, 4: D} /// ``` factory LinkedHashMap.of(Map other) => LinkedHashMap()..addAll(other); /// Creates a [LinkedHashMap] where the keys and values are computed from the /// [iterable]. /// /// For each element of the [iterable], this constructor computes a key/value /// pair by applying [key] and [value] respectively. /// /// The keys of the key/value pairs do not need to be unique. The last /// occurrence of a key will simply overwrite any previous value. /// /// If no values are specified for [key] and [value], the default is the /// both default to the identity function. /// Example: /// ```dart /// final numbers = [11, 12, 13, 14]; /// final mapFromIterable = /// LinkedHashMap.fromIterable(numbers, key: (i) => i, value: (i) => i * i); /// print(mapFromIterable); // {11: 121, 12: 144, 13: 169, 14: 196} /// ``` factory LinkedHashMap.fromIterable( Iterable iterable, { K Function(dynamic element)? key, V Function(dynamic element)? value, }) { LinkedHashMap map = LinkedHashMap(); MapBase._fillMapWithMappedIterable(map, iterable, key, value); return map; } /// Creates a [LinkedHashMap] associating the given [keys] to [values]. /// /// This constructor iterates over [keys] and [values] and maps each element of /// [keys] to the corresponding element of [values]. /// /// If [keys] contains the same object multiple times, the last occurrence /// overwrites the previous value. /// /// It is an error if the two [Iterable]s don't have the same length. /// Example: /// ```dart /// final values = [0.06, 0.81, 1, 0.11]; /// final keys = ['Mercury', 'Venus', 'Earth', 'Mars']; /// final mapFromIterables = LinkedHashMap.fromIterables(keys, values); /// print(mapFromIterables); /// // {Mercury: 0.06, Venus: 0.81, Earth: 1, Mars: 0.11} /// ``` factory LinkedHashMap.fromIterables(Iterable keys, Iterable values) { LinkedHashMap map = LinkedHashMap(); MapBase._fillMapWithIterables(map, keys, values); return map; } /// Creates a [LinkedHashMap] containing the entries of [entries]. /// /// Returns a new `LinkedHashMap` where all entries of [entries] /// have been added in iteration order. /// /// If multiple [entries] have the same key, /// later occurrences overwrite the earlier ones. /// Example: /// ```dart /// final numbers = [11, 12, 13, 14]; /// final map = LinkedHashMap.fromEntries(numbers.map((i) => MapEntry(i, i * i))); /// print(map); // {11: 121, 12: 144, 13: 169, 14: 196} /// ``` factory LinkedHashMap.fromEntries(Iterable> entries) => LinkedHashMap()..addEntries(entries); }