Swift 3 introduced finer-grained control over what can access what in your code. The addition of 2 keywords made things less obvious, however. Here is a cheatsheet to help with the transition:

• Private: Entity can only be accessed within the same scope it was defined in. A private class can only be subclassed by another private class defined in the same scope.

• File private: Entity can only be accessed within the same file. You can subclass fileprivate classes and override their fileprivate methods and properties.

• Internal: Entity can only be accessed within the same module, i.e. app or framework target. This is the default if no access keyword is specified. You can subclass classes and override their non-private methods and properties.

• Public: Entity can be accessed from within other modules. Classes cannot be subclassed.

• Open: Entity can be accessed from within other modules. Classes can be subclassed in other modules if they are marked as open. Each method and property needs to be marked as open to be overridable in subclasses.