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reimplement MapEntry as a record #61071

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reimplement MapEntry as a record #61071

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21 changes: 4 additions & 17 deletions sdk/lib/core/map.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -478,21 +478,15 @@ abstract interface class Map<K, V> {
/// ]);
/// print(map); // {1: A, 2: B, 3: C, 4: D}
/// ```
///
/// Do not extend or implement the `MapEntry` class.
/// If the Dart language introduces value types,
/// the `MapEntry` class will be changed to such a type,
/// and will likely no longer be able to be implemented or extended
/// by classes.
final class MapEntry<K, V> {
extension type const MapEntry<K, V>.fromPair((K, V) asPair) implements Object {
/// The key of the entry.
///
/// ```dart
/// final map = {'theKey': 'theValue'}; // Map<String, String>
/// var entry = map.entries.first; // MapEntry<String, String>
/// print(entry.key); // 'theKey'
/// ```
final K key;
K get key => asPair.$1;

/// The value associated to [key] in a map.
///
Expand All @@ -501,15 +495,8 @@ final class MapEntry<K, V> {
/// var entry = map.entries.first; // MapEntry<String, String>
/// print(entry.value); // 'theValue'
/// ```
final V value;
V get value => asPair.$2;

/// Creates an entry with [key] and [value].
const factory MapEntry(K key, V value) = MapEntry<K, V>._;

const MapEntry._(this.key, this.value);

/// String representation intended for debugging only.
///
/// Not guaranteed to be stable over time.
String toString() => "MapEntry($key: $value)";
const MapEntry(K key, V value) : this.fromPair((key, value));
}