Key-Value Coding @UnionOfObjects

Question

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?

Accepted Answer

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.

Key-Value Coding @UnionOfObjects

Solution

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