title: Prototypical OO: extending an object that is not "class-like"
body: <p>Prototypical OO talks about getting rid of the class-instance distinction and having only objects. Objects inherit from other object.</p>
  
  <p>However, all examples that I've seen end up having "class-like" objects and "instance-like" objects. The former have a set of methods and maybe constants and are typically immutable once they're built. The latter contain actual instance data, delegate method calls to "class-like" ones and can be either mutable or immutable as needed.</p>
  
  <p>Are there any good examples where having something which behaves like both of them is beneficial to the application architecture? Can something be though of as an instance with, let's say, mutable fields, and, at the same time, a prototype for a number of other objects? Not a contrived example, but something that looks like it makes a real system easier to understand, maintain, etc? </p>