This, is actually the wrong conclusion. The entire purpose of the “inner class” is to provide value semantics while maintaining effeciency of implementation.
Is that an opinion? Or was there a meeting when the "entire purpose" of inner classes was established and I wasn't invited? Sure, they can be used for efficiency, but they can also be used for other purposes, including inner mutation.
Just for starters, Mike Ash seems to have uncovered that inner classes are used inside the standard library to provide destructors:
Destruction can be solved by using a class, which provides deinit. The pointer can be destroyed there. class doesn't have value semantics, but we can solve this by using class for the implementation of the struct, and exposing the struct as the external interface to the array.
So to say that the "entire purpose" of inner classes is efficiency is I think plainly false; they are used for many reasons. E