On Sep 20, 6:52 am, Ben Finney <[EMAIL PROTECTED]> wrote: > Michele Simionato <[EMAIL PROTECTED]> writes: > > Since the language we have does have multiple inheritance, let's > > use it to implement mixins. > > ... > > So, multiple inheritance is giving us very little for the point of > > view of mixins; OTOH, multiple inheritance is giving us a lot of > > headaches for what concerns cooperative methods. > > I may be obtuse, but the above statements seem to be professing > contradictory viewpoints.
How so? A language doesn't need MI to have mixins (e.g. Ruby does this). This doesn't seem to contradict that MI is, in general, a horrible solution to most problems -- one example being the general difficulty in groking cooperative (super) methods. A single- inheritance language, otoh, is also a chore to work with (for a specific subset of designs) -- unless there is _some_ way to do mixins. But for the general case I agree with Micele that delegation is the better solution (Explicit is better than implicit). > Do you think multiple inheritance should or should not be used in > Python to do what mixins do? Michele already answered this, Python has MI so it would just be confusing to implement mixins any other way. > > My point was that even if Python had been implemented without > > multiple inheritance, it would have been simple to implement mixins, > > or by copying the methods, or by dispatching with __getattr__. > > Can you give a code example of how you think mixins should be > implemented in Python, assuming the absence of multiple inheritance? Googling for "Ruby mixins tutorial" gave me the following link: http://www.juixe.com/techknow/index.php/2006/06/15/mixins-in-ruby/ If I tell you that self.something is written @something in Ruby, and inheritance is written class Base < Parent (as opposed to class Base(Parent):) everything else should be understandable..? How to implement include and extend in Python is left as an excercise for the reader. -- bjorn -- http://mail.python.org/mailman/listinfo/python-list
