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maps.dart
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maps.dart
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// Copyright (c) 2012, 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;
/// Base class for implementing a [Map].
///
/// This class has a basic implementation of all but five of the members of
/// [Map].
/// A basic `Map` class can be implemented by extending this class and
/// implementing `keys`, `operator[]`, `operator[]=`, `remove` and `clear`.
/// The remaining operations are implemented in terms of these five.
///
/// The `keys` iterable should have efficient [Iterable.length] and
/// [Iterable.contains] operations, and it should catch concurrent modifications
/// of the keys while iterating.
///
/// A more efficient implementation is usually possible by overriding
/// some of the other members as well.
abstract class MapBase<K, V> extends MapMixin<K, V> {
static String mapToString(Map<Object?, Object?> m) {
// Reuses the list in IterableBase for detecting toString cycles.
if (_isToStringVisiting(m)) {
return '{...}';
}
var result = StringBuffer();
try {
_toStringVisiting.add(m);
result.write('{');
bool first = true;
m.forEach((Object? k, Object? v) {
if (!first) {
result.write(', ');
}
first = false;
result.write(k);
result.write(': ');
result.write(v);
});
result.write('}');
} finally {
assert(identical(_toStringVisiting.last, m));
_toStringVisiting.removeLast();
}
return result.toString();
}
static Object? _id(Object? x) => x;
/// Fills a [Map] with key/value pairs computed from [iterable].
///
/// This method is used by [Map] classes in the named constructor
/// `fromIterable`.
static void _fillMapWithMappedIterable(
Map<Object?, Object?> map,
Iterable<Object?> iterable,
Object? Function(Object? element)? key,
Object? Function(Object? element)? value) {
key ??= _id;
value ??= _id;
if (key == null) throw "!"; // TODO(38493): The `??=` should promote.
if (value == null) throw "!"; // TODO(38493): The `??=` should promote.
for (var element in iterable) {
map[key(element)] = value(element);
}
}
/// Fills a map by associating the [keys] to [values].
///
/// This method is used by [Map] classes in the named constructor
/// `fromIterables`.
static void _fillMapWithIterables(Map<Object?, Object?> map,
Iterable<Object?> keys, Iterable<Object?> values) {
Iterator<Object?> keyIterator = keys.iterator;
Iterator<Object?> valueIterator = values.iterator;
bool hasNextKey = keyIterator.moveNext();
bool hasNextValue = valueIterator.moveNext();
while (hasNextKey && hasNextValue) {
map[keyIterator.current] = valueIterator.current;
hasNextKey = keyIterator.moveNext();
hasNextValue = valueIterator.moveNext();
}
if (hasNextKey || hasNextValue) {
throw ArgumentError("Iterables do not have same length.");
}
}
}
/// Mixin implementing a [Map].
///
/// This mixin has a basic implementation of all but five of the members of
/// [Map].
/// A basic `Map` class can be implemented by mixin in this class and
/// implementing `keys`, `operator[]`, `operator[]=`, `remove` and `clear`.
/// The remaining operations are implemented in terms of these five.
///
/// The `keys` iterable should have efficient [Iterable.length] and
/// [Iterable.contains] operations, and it should catch concurrent modifications
/// of the keys while iterating.
///
/// A more efficient implementation is usually possible by overriding
/// some of the other members as well.
abstract class MapMixin<K, V> implements Map<K, V> {
Iterable<K> get keys;
V? operator [](Object? key);
operator []=(K key, V value);
V? remove(Object? key);
// The `clear` operation should not be based on `remove`.
// It should clear the map even if some keys are not equal to themselves.
void clear();
Map<RK, RV> cast<RK, RV>() => Map.castFrom<K, V, RK, RV>(this);
void forEach(void action(K key, V value)) {
for (K key in keys) {
action(key, this[key] as V);
}
}
void addAll(Map<K, V> other) {
for (K key in other.keys) {
this[key] = other[key] as V;
}
}
bool containsValue(Object? value) {
for (K key in keys) {
if (this[key] == value) return true;
}
return false;
}
V putIfAbsent(K key, V ifAbsent()) {
if (containsKey(key)) {
return this[key] as V;
}
return this[key] = ifAbsent();
}
V update(K key, V update(V value), {V Function()? ifAbsent}) {
if (this.containsKey(key)) {
return this[key] = update(this[key] as V);
}
if (ifAbsent != null) {
return this[key] = ifAbsent();
}
throw ArgumentError.value(key, "key", "Key not in map.");
}
void updateAll(V update(K key, V value)) {
for (var key in this.keys) {
this[key] = update(key, this[key] as V);
}
}
Iterable<MapEntry<K, V>> get entries {
return keys.map((K key) => MapEntry<K, V>(key, this[key] as V));
}
Map<K2, V2> map<K2, V2>(MapEntry<K2, V2> transform(K key, V value)) {
var result = <K2, V2>{};
for (var key in this.keys) {
var entry = transform(key, this[key] as V);
result[entry.key] = entry.value;
}
return result;
}
void addEntries(Iterable<MapEntry<K, V>> newEntries) {
for (var entry in newEntries) {
this[entry.key] = entry.value;
}
}
void removeWhere(bool test(K key, V value)) {
var keysToRemove = <K>[];
for (var key in keys) {
if (test(key, this[key] as V)) keysToRemove.add(key);
}
for (var key in keysToRemove) {
this.remove(key);
}
}
bool containsKey(Object? key) => keys.contains(key);
int get length => keys.length;
bool get isEmpty => keys.isEmpty;
bool get isNotEmpty => keys.isNotEmpty;
Iterable<V> get values => _MapBaseValueIterable<K, V>(this);
String toString() => MapBase.mapToString(this);
}
/// Basic implementation of an unmodifiable [Map].
///
/// This class has a basic implementation of all but two of the members of
/// an umodifiable [Map].
/// A simple unmodifiable `Map` class can be implemented by extending this
/// class and implementing `keys` and `operator[]`.
///
/// Modifying operations throw when used.
/// The remaining non-modifying operations are implemented in terms of `keys`
/// and `operator[]`.
///
/// The `keys` iterable should have efficient [Iterable.length] and
/// [Iterable.contains] operations, and it should catch concurrent modifications
/// of the keys while iterating.
///
/// A more efficient implementation is usually possible by overriding
/// some of the other members as well.
abstract class UnmodifiableMapBase<K, V> = MapBase<K, V>
with _UnmodifiableMapMixin<K, V>;
/// Implementation of [Map.values] based on the map and its [Map.keys] iterable.
///
/// Iterable that iterates over the values of a `Map`.
/// It accesses the values by iterating over the keys of the map, and using the
/// map's `operator[]` to lookup the keys.
class _MapBaseValueIterable<K, V> extends EfficientLengthIterable<V> {
final Map<K, V> _map;
_MapBaseValueIterable(this._map);
int get length => _map.length;
bool get isEmpty => _map.isEmpty;
bool get isNotEmpty => _map.isNotEmpty;
V get first => _map[_map.keys.first] as V;
V get single => _map[_map.keys.single] as V;
V get last => _map[_map.keys.last] as V;
Iterator<V> get iterator => _MapBaseValueIterator<K, V>(_map);
}
/// Iterator created by [_MapBaseValueIterable].
///
/// Iterates over the values of a map by iterating its keys and lookup up the
/// values.
class _MapBaseValueIterator<K, V> implements Iterator<V> {
final Iterator<K> _keys;
final Map<K, V> _map;
V? _current;
_MapBaseValueIterator(Map<K, V> map)
: _map = map,
_keys = map.keys.iterator;
bool moveNext() {
if (_keys.moveNext()) {
_current = _map[_keys.current];
return true;
}
_current = null;
return false;
}
V get current => _current as V;
}
/// Mixin that overrides mutating map operations with implementations that
/// throw.
abstract class _UnmodifiableMapMixin<K, V> implements Map<K, V> {
/// This operation is not supported by an unmodifiable map.
void operator []=(K key, V value) {
throw UnsupportedError("Cannot modify unmodifiable map");
}
/// This operation is not supported by an unmodifiable map.
void addAll(Map<K, V> other) {
throw UnsupportedError("Cannot modify unmodifiable map");
}
/// This operation is not supported by an unmodifiable map.
void addEntries(Iterable<MapEntry<K, V>> entries) {
throw UnsupportedError("Cannot modify unmodifiable map");
}
/// This operation is not supported by an unmodifiable map.
void clear() {
throw UnsupportedError("Cannot modify unmodifiable map");
}
/// This operation is not supported by an unmodifiable map.
V? remove(Object? key) {
throw UnsupportedError("Cannot modify unmodifiable map");
}
/// This operation is not supported by an unmodifiable map.
void removeWhere(bool test(K key, V value)) {
throw UnsupportedError("Cannot modify unmodifiable map");
}
/// This operation is not supported by an unmodifiable map.
V putIfAbsent(K key, V ifAbsent()) {
throw UnsupportedError("Cannot modify unmodifiable map");
}
/// This operation is not supported by an unmodifiable map.
V update(K key, V update(V value), {V Function()? ifAbsent}) {
throw UnsupportedError("Cannot modify unmodifiable map");
}
/// This operation is not supported by an unmodifiable map.
void updateAll(V update(K key, V value)) {
throw UnsupportedError("Cannot modify unmodifiable map");
}
}
/// Wrapper around a class that implements [Map] that only exposes `Map`
/// members.
///
/// A simple wrapper that delegates all `Map` members to the map provided in the
/// constructor.
///
/// Base for delegating map implementations like [UnmodifiableMapView].
class MapView<K, V> implements Map<K, V> {
final Map<K, V> _map;
const MapView(Map<K, V> map) : _map = map;
Map<RK, RV> cast<RK, RV>() => _map.cast<RK, RV>();
V? operator [](Object? key) => _map[key];
void operator []=(K key, V value) {
_map[key] = value;
}
void addAll(Map<K, V> other) {
_map.addAll(other);
}
void clear() {
_map.clear();
}
V putIfAbsent(K key, V ifAbsent()) => _map.putIfAbsent(key, ifAbsent);
bool containsKey(Object? key) => _map.containsKey(key);
bool containsValue(Object? value) => _map.containsValue(value);
void forEach(void action(K key, V value)) {
_map.forEach(action);
}
bool get isEmpty => _map.isEmpty;
bool get isNotEmpty => _map.isNotEmpty;
int get length => _map.length;
Iterable<K> get keys => _map.keys;
V? remove(Object? key) => _map.remove(key);
String toString() => _map.toString();
Iterable<V> get values => _map.values;
Iterable<MapEntry<K, V>> get entries => _map.entries;
void addEntries(Iterable<MapEntry<K, V>> entries) {
_map.addEntries(entries);
}
Map<K2, V2> map<K2, V2>(MapEntry<K2, V2> transform(K key, V value)) =>
_map.map<K2, V2>(transform);
V update(K key, V update(V value), {V Function()? ifAbsent}) =>
_map.update(key, update, ifAbsent: ifAbsent);
void updateAll(V update(K key, V value)) {
_map.updateAll(update);
}
void removeWhere(bool test(K key, V value)) {
_map.removeWhere(test);
}
}
/// View of a [Map] that disallow modifying the map.
///
/// A wrapper around a `Map` that forwards all members to the map provided in
/// the constructor, except for operations that modify the map.
/// Modifying operations throw instead.
class UnmodifiableMapView<K, V> extends MapView<K, V>
with _UnmodifiableMapMixin<K, V> {
UnmodifiableMapView(Map<K, V> map) : super(map);
Map<RK, RV> cast<RK, RV>() =>
UnmodifiableMapView<RK, RV>(_map.cast<RK, RV>());
}