CODEWITHSUNDEEP
objective-cnsorderedset
user4951
user4951

Reputation: 33138

Array from set: why does NSSet use allObjects, while NSOrderedSet uses array?

In Foundation, if I want to convert a set to an NSArray, I can use:

Why are these different?

Upvotes: 21

Views: 9354

Answers (3)

Clay Bridges
Clay Bridges

Reputation: 11890

While there are other differences†, .allObjects does not imply a definite ordering, and .array does; and that's exactly what you are getting.

† .array returns a live proxy of the underlying NSOrderedSet, and if the underlying ordered set changes, the proxy will change with it.

Upvotes: 6

OmniB
OmniB

Reputation: 111

Also... The NSArray returned by 'allObjects' is a copy of the values in the set.

But the NSArray returned by 'array' is a proxy of the objects in the set.

Thus if you change the value of any object in the set, you will change the value of the object in the array. A copy of the ordered set is not being made. So the two properties have different names because they do different things.

Upvotes: 1

Wade Tregaskis
Wade Tregaskis

Reputation: 2018

Speculation, but:

Because when NSSet was created the only other major collection type was NSArray, which was (and still is, largely) the most common collection type. So a method called "allObjects" would obviously return an NSArray.

When NSOrderedSet was added much more recently, it had to deal with the existence of prior collections - primarily, NSArray and NSSet. So an "allObjects" method would be ambiguous. Ergo it has two methods, -array and -set.

And/or, the -array and -set methods return proxies to what are likely the same or similar classes used internally. So in a functional sense they're a little different - those proxies will see mutations made on the original NSOrderedSet. -allObjects on the other hand does not - it genuinely creates an independent array, since its internal storage is likely a hashtable or similar that isn't readily proxied.

Upvotes: 21

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