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Documentation update for LinkedHashMap

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Added example code blocks for LinkedHashMap class and includes some minor textual updates to comments.

Closes https://github.com/dart-lang/sdk/pull/47706
https://github.com/dart-lang/sdk/pull/47706

GitOrigin-RevId: 86bded093f3304169aa97d7d6d0e64932ad184be
Change-Id: I8aa18dc04fb67498277c214916a3076428244a00
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/220301
Reviewed-by: Lasse R.H. Nielsen <lrn@google.com>
This commit is contained in:
Jukka-Pekka Siitonen 2021-11-25 15:31:25 +00:00 committed by Lasse R.H. Nielsen
parent 3875e69a79
commit a98368c250
1 changed files with 132 additions and 8 deletions
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140
sdk/lib/collection/linked_hash_map.dart
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@ -4,7 +4,16 @@
part of dart.collection;
/// A hash-table based implementation of [Map].
/// 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.
@ -14,11 +23,93 @@ part of dart.collection;
/// 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].
/// ```
/// 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].
/// ```
/// 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.
/// ```
/// 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].
/// ```
/// 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].
/// ```
/// final earthExists = planetsByDiameter.containsValue('Earth'); // true
/// final saturnExists = planetsByDiameter.containsValue('Saturn'); // false
/// ```
/// To remove an entry with a specific key, use [remove].
/// ```
/// 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].
/// ```
/// 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].
/// ```
/// 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].
/// ```
/// 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].
/// ```
/// 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 class LinkedHashMap<K, V> implements Map<K, V> {
/// Creates an insertion-ordered hash-table based [Map].
///
@ -26,7 +117,7 @@ abstract class LinkedHashMap<K, V> implements Map<K, V> {
/// new keys. If [equals] is omitted, the key's own [Object.==] is used
/// instead.
///
/// Similar, if [hashCode] is provided, it is used to produce a hash value
/// 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.
///
@ -35,7 +126,7 @@ abstract class LinkedHashMap<K, V> implements Map<K, V> {
/// of an object, or what it compares equal to, should not change while the
/// object is in the table. If it does change, the result is unpredictable.
///
/// If you supply one of [equals] and [hashCode],
/// 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.
@ -73,7 +164,7 @@ abstract class LinkedHashMap<K, V> implements Map<K, V> {
/// Creates an insertion-ordered identity-based map.
///
/// Effectively a shorthand for:
/// Effectively shorthand for:
/// ```dart template:expression
/// LinkedHashMap<K, V>(equals: identical,
/// hashCode: identityHashCode)
@ -84,6 +175,12 @@ abstract class LinkedHashMap<K, V> implements Map<K, V> {
///
/// 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 = <num, Object>{1: 'A', 2: 'B', 3: 'C'};
/// final fromBaseMap = LinkedHashMap<int, String>.from(baseMap);
/// print(fromBaseMap); // {1: A, 2: B, 3: C}
/// ```
factory LinkedHashMap.from(Map<dynamic, dynamic> other) {
LinkedHashMap<K, V> result = LinkedHashMap<K, V>();
other.forEach((dynamic k, dynamic v) {
@ -93,20 +190,33 @@ abstract class LinkedHashMap<K, V> implements Map<K, V> {
}
/// Creates a [LinkedHashMap] that contains all key value pairs of [other].
/// Example:
/// ```dart
/// final baseMap = <int, String> {3: 'A', 2: 'B', 1: 'C', 4: 'D'};
/// final mapOf = LinkedHashMap<num, Object>.of(baseMap);
/// print(mapOf); // {3: A, 2: B, 1: C, 4: D}
/// ```
factory LinkedHashMap.of(Map<K, V> other) =>
LinkedHashMap<K, V>()..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.
/// 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
/// identity function.
/// 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<K, V> map = LinkedHashMap<K, V>();
@ -123,6 +233,14 @@ abstract class LinkedHashMap<K, V> implements Map<K, V> {
/// 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<K> keys, Iterable<V> values) {
LinkedHashMap<K, V> map = LinkedHashMap<K, V>();
MapBase._fillMapWithIterables(map, keys, values);
@ -136,6 +254,12 @@ abstract class LinkedHashMap<K, V> implements Map<K, V> {
///
/// 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}
/// ```
@Since("2.1")
factory LinkedHashMap.fromEntries(Iterable<MapEntry<K, V>> entries) =>
LinkedHashMap<K, V>()..addEntries(entries);