Where is the definition of `map.clear()`?-CodePudding

I'm checking the implementation of Map. (map.dart in dart:collection)

I find void clear(); in abstract class Map<K, V>. clear() doesn't have any implementation and class Map doesn't extend/implement any other classes. But I can still call clear().

example

Map<int, int> m = <int, int>{1: 1, 2: 2};
m.clear();

Where can I find the implementation of clear()?

CodePudding user response：

My answer is based on the assumption that you want the implementation used when Dart is running natively and not on the web.

The default Map in Dart is a LinkedHashMap. There are several layers before getting the implementation of clear() but I expect this is the one you are looking for:

  void clear() {
    if (!isEmpty) {
      _index = _uninitializedIndex;
      _hashMask = _HashBase._UNINITIALIZED_HASH_MASK;
      _data = _uninitializedData;
      _usedData = 0;
      _deletedKeys = 0;
    }
  }

https://github.com/dart-lang/sdk/blob/2.15.1/sdk/lib/_internal/vm/lib/compact_hash.dart#L333-L341

CodePudding user response：

The {} notation creates a LinkedHashMap and that's where you'll find the implementation. See:

import 'dart:collection';

void main () {

  Map<int, int> m = <int, int>{1: 1, 2: 2};
  if(m is LinkedHashMap) {
    print("It's a LinkedHashMap!");
  }
}

Output:

It's a LinkedHashMap!