p is a pointer to the collection’s mutable contiguous storage. If no such storage exists, it is first created. If the collection does not support an internal representation in a form of mutable contiguous storage,
body is not called and
nil is returned.
- Xcode 10.2+
- Swift Standard Library
Often, the optimizer can eliminate bounds- and uniqueness-checks within an algorithm, but when that fails, invoking the same algorithm on
body\ ’s argument lets you trade safety for speed.