Inserts the given element in the set if it is not already present.
- Xcode 8.0+
An element to insert into the set.
(true, new if
new was not contained in the set. If an element equal to
new was already contained in the set, the method returns
(false, old, where
old is the element that was equal to
new. In some cases,
old may be distinguishable from
new by identity comparison or some other means.
If an element equal to
new is already contained in the set, this method has no effect. In the following example, a new element is inserted into
class, a set of days of the week. When an existing element is inserted, the
class set does not change.