dart:core

add abstract method

bool add( E value)

Adds value to the set.

Returns true if value (or an equal value) was not yet in the set. Otherwise returns false and the set is not changed.

Example:

var set = new Set();
var time1 = new DateTime.fromMillisecondsSinceEpoch(0);
var time2 = new DateTime.fromMillisecondsSinceEpoch(0);
// time1 and time2 are equal, but not identical.
Expect.isTrue(time1 == time2);
Expect.isFalse(identical(time1, time2));
set.add(time1);  // => true.
// A value equal to time2 exists already in the set, and the call to
// add doesn't change the set.
set.add(time2);  // => false.
Expect.isTrue(set.length == 1);
Expect.isTrue(identical(time1, set.first));

Source

bool add(E value);