Value Coding @UnionOfObjects
I can't figure out what @UnionOfObjects offers that a simple valueForKey: or valueForKeyPath: can't do.
Apple docs:
The @unionOfObjects operator returns an array containing the distinct objects in the property specified by the key path to the right of the operator. Unlike “@distinctUnionOfObjects,” duplicate objects are not removed. The following example returns the payee property values for the transactions in transactions:
NSArray *payees = [transactions valueForKeyPath:@"@unionOfObjects.payee"];
The resulting payees array contains the following strings: Green Power, Green Power, Green Power, Car Loan, Car Loan, Car Loan, General Cable, General Cable, General Cable, Mortgage, Mortgage, Mortgage, Animal Hospital.
In the above example,
NSArray *payees = [transactions valueForKey:@"payee"];
would return the same array of values, but with less code. What am I missing?
All I can think of immediately is that it "returns an array containing ..." (emphasis mine). So it'll be convenient for:
NSSet *someSet = ...;
NSArray *result = [someSet valueForKey:@"@unionOfObjects.whatever"];
It's therefore useful anywhere in Cocoa bindings where you want an NSSet (or other non-array collection) to push data into an NSArray shaped hole.
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