add
Adds element if no equal element is already present.
A duplicate retains the original stored element and leaves existing iterators valid. A new element increases size, may grow the backing table and invalidates existing iterators.
Return
true if a new element was inserted, or false for a duplicate.
Parameters
element
value to add, with stable equality and hashing while stored.
Throws
if inserting a new element exceeds the supported size or bucket capacity.