On Thu, Oct 17, 2013 at 5:49 PM, Peter Cacioppi <peter.cacio...@gmail.com> wrote: > I don't know if I want to step into the flames here, but my understanding has > always been that in the absence of polymorphism the best you can do is > "object based" programming instead of "object oriented" programming. > > Object oriented programming takes things further, most significantly by > introducing the idea that the object reference you are referencing might be a > run time dependent sub-class. Even Python, which isn't strongly typed, > manages polymorphism by allowing the self argument to a sub-class of the > method class.
What you've said here is that "without polymorphism, you can't have polymorphism". :) The OS/2 PM with SOM (System Object Model) classes does give polymorphic functionality; here's a bit of an example: (Reference: http://www.markcrocker.com/rexxtipsntricks/rxtt28.2.0299.html - class hierarchy, standard classes only) Part way down you'll see WPFolder. It's a subclass of WPFileSystem (aka "stuff backed by the disk" as opposed to abstract objects), which is a subclass of WPObject (aka "stuff you can see and click on"), which is a subclass of SOMObject (aka "stuff"). The WPFolder class defines a whole pile of functionality, and its code is all stored in some library somewhere, as a binary on the disk. Well and good. Now look at the WPRootFolder class. It's a subclass of WPFolder and adds a few extra bits and bobs designed for the root of any particular drive (OS/2 uses an MS-DOS style of drive letters for volumes, rather than a Unix-style mount points) - menu items for formatting the drive, getting extra info perhaps, whatever. But most of its functionality comes from WPFolder. When a WPFolder method is called on a WPRootFolder, the code has to handle the fact that it's working with a subclass of that object. As long as the proper SOM boilerplate is maintained correctly, the WPFolder code won't even be aware that it's operating on a WPRootFolder. That's polymorphism, and it's all done in a completely cross-language way :) (There are additional complications, as it's possible for a subclass to WPReplaceClass (I'm probably misremembering the function name) itself into the position of the parent class, which messes up the hierarchy a bit - it still all works, but it's less clean to describe. Most things work the way I'm describing.) ChrisA -- https://mail.python.org/mailman/listinfo/python-list
