If an object equal to object
is in the set, return it.
Checks if there is an object in the set that is equal to object
. If so, that object is returned, otherwise returns null.
E lookup(Object element);
© 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dartlang.org/stable/2.0.0/dart-collection/SetMixin/lookup.html