Subclassing vs Extension in swift

Question

I want to customise one UITextField for some reason. So currently I subclassed it and added few methods.

Instead of that can I use extension over UITextField ? Which is

Answer 1

As a general rule of thumb (YMMV):

• Are you adding general-purpose functionalities that should be available to every UITextField? If so, make an extension. All UITextField instances can call the new methods.
• Are you adding functionality that should be restricted to special instances of UITextField that you would identify precisely? If so, make a subclass. Only the instances of the subclass can use the new methods.

There are other technical considerations, like extensions can't add fields, for instance.

Answer 2

Swift extensions can't be overridden. So If you would like to create a testing purpose subclasses then you will be limited.