Before M4.5 objects were instantiated using a ComponentProvider which eventually delegated to Classes.getClassFactory().newInstance(). With M4.5 IoC was introduced and the current ComponentProvider info.magnolia.objectfactory.guice.GuiceComponentProvider is no longer aware of the ClassFactory. However, as the DefaultClassFactory can be replaced with a custom one (like e.g. our Groovy module does) that means that instantiating new objects with a custom class factory no longer works. This particularly affects the Groovy module and its ability to replace Java classes in config with Groovy ones and hot deploy and change them on the fly.

It was decided to make our current default ComponentProvider aware of ClassFactory again. This will happen through ObjectManufacturer which is eventually used to create class instances. The new interface will be implemented by custom class factories and ObjectManufacturer will call the interface's new method delegating to the custom cf which will try to re-load (by recompiling if necessary) the class.

Some concerns were expressed as to a performance penalty due to this additional check but, as far as I could see in my basic measurements, the overload seems to be negligible.
Here I am comparing the execution time of ObjectManufacturer.newInstance() with and without my changes. The table shows most of the classes instantiated by Magnolia when rendering the home page of the travel demo. The largest numbers are of course for the Groovy foo.TestModel class especially when it needs recompiling cause the source has changed (more precisely because it's newer).