gistfile1.ts

import { mixin, declareFrom, after } from 'core/traits' or 'core/compose'

class Request {
	get() { }
}
class Cache {
	@after /* add something to the method so that mixin knows that it should run after the method it is overriding? */
	get() {
	}
	invalidate() { }
}
@mixin(Cache) /* this could mixin the functionality from Cache, I think, but of course won't add type information from Cache */
class UserRequestMemory extends Request {
  /* user can explicitly declare which methods they will actually need, (and even choose which mixin to take precedent),
  for example with Cache, most of it is just about altering behavior of existing methods, but if we did need to access a Cache method: */
	@declareFrom(Cache)
	invalidate() { throw }
}

var store = new UserRequestMemory();
store.get();
store.invalidate();