Swift has rich value types, which is a new experience for many software developers. This has opened the door for the functionalists to ride in.
What I call “functionalism” is really the philosophy of functional programming, which is in fact a very old idea. The idea is that a lot of bugs in programming today are due to having the wrong state. For example, the Heartbleed bug happened because someone re-used the same array for a different purpose. So the solution, clearly, is to get rid of mutable arrays, and mutable variables, and the assignment operator, and you can’t have the heartbleed bug now. (Why they did not also get rid of the programmer is an exercise left to the reader.)