Removes the first element of the set.
- Xcode 6.3+
- Swift Standard Library
A member of the set.
Because a set is not an ordered collection, the “first” element may not be the first element that was added to the set. The set must not be empty.
Complexity: Amortized O(1) if the set does not wrap a bridged
NSSet. If the set wraps a bridged
NSSet, the performance is unspecified.