Testing Membership in a Collection

Each collection class has its own way of testing for membership. You can add code after the last step in the previous Try It Yourself to test for membership. Listing 15.3 shows how you can add your objects to a set. You can then test to see if one of the objects is in that set using the member method. It will return the object or nil if the object is not in the collection.

– (id)member:(id)object

The code snippet is shown in Listing 15.3.

Listing 15.3. Test for Membership in a Set

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NSSet *mySet = [NSSet setWithObjects: myString, myNumber, myDate, nil];
NSLog (@"mySet:%@\n", [mySet description]);

anObject = [mySet member:myDate];
NSLog(@"member:%@\n",[anObject description]);

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Experiment with adding other objects (and not adding objects) to watch the results. You can also simply ask if an object is a member of a collection (the result is YES or NO rather than the object itself).