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

Question

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()?

Solution

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

Comments

[Philipos D.]

Can you check what it extends / implements? Also when you try to Go To Definition in the IDE, where does it lead you?

[Yunus Kocatas]

after clear() operation map will be empty {}

[julemand101]

Yeah, not really helpful since this clue just points you to: github.com/dart-lang/sdk/blob/… which does not contain much implementation and not for clear(). ;)