Return a set containing the results of invoking
value on each of the receiving set's members.
- iOS 2.0+
- macOS 10.4+
- tvOS 9.0+
- watchOS 2.0+
The name of one of the properties of the receiving set's members.
A set containing the results of invoking
value (with the argument
key) on each of the receiving set's members.
The returned set might not have the same number of members as the receiving set. The returned set will not contain any elements corresponding to instances of
nil (note that this is in contrast with
NSArray’s implementation, which may put
NSNull values in the arrays it returns).