The implementation of overriding the scope's $watch method is fairly straight forward.

We gave our optimization directive a fairly high priority so that it was guaranteed to be run first (among all the other directives on an element).

When the optimization directive ran, it just modified the scope variable passed to it, saving a reference to the original scope.$watch method and then setting scope.$watch to a new function we created. Inside that function, it does invoke the original scope.$watch.

We also had to override scope.$new to guarantee that any child elements, if they create new scopes, also create scopes with our override $watch method.