Метод clear

void clear()

Удаляет все элементы из множества.

final characters = <String>{'A', 'B', 'C'};
characters.clear(); // {}

Реализация

void clear();

© 2012 the Dart project authors
Licensed under the BSD 3-Clause "New" or "Revised" License.
https://api.dart.dev/stable/2.18.5/dart-core/Set/clear.html