I'm creating objects and adding them to a set using -[NSOrderedMutableSet addObject:], but I discovered that only duplicates of the objects themselves are checked for -- the object pointer's address presumably, and that it's possible to add multiple objects that have identical content.
For example:
SomeObject* object = [SomeObject alloc] initWithStuff:stuff];
SomeObject* object2 = [SomeObject alloc] initWithStuff:stuff];
[set addObject:object];
[set addObject:object];
[set addObject:object1];
[set addObject:object2];
The count will be 2.
This makes me wonder what the point of these classes is? Under what circumstances might one have an object and not know if the object itself had already been added to a collection, rather than the data contained within the object?
Whats the easiest way (or what class should I use) to use to ensure the set only contains one of each object based on content?
The way you are looking is the right way, you are forgetting a small detail: how could the NSMutableOrderedSet class know about which instances of SomeObject contain same values?
The answer is simple: you must provide your own implementations of
- (BOOL)isEqual:(id)anObject
- (NSUInteger)hash
So that your instances will return true when compared with same internal values, and two instances with same data will have same hashcode.
Apart from this sets are rather useful because they give you better complexity on checking if an instance is contained in a set or not, and you can quickly do many logical operations on them, like intersection, union, difference and whatever.