Duncan Booth wrote: > Alex Martelli wrote: > > >> What I think I'm trying to get at is that I believe that most > >> situations where someone actually tries to do something in the base > >> initialiser which requires calling a virtual method are probably also > >> cases where the initialiser is doing too much: i.e. separating the > >> construction/initialisation from actually doing something is usually > >> a good idea. > > > > But why should that be? Template Method is perhaps the MOST generally > > useful design pattern -- why would it be any less useful in > > initialization than elsewhere?! > > > Because it is error prone? > > Any method which is called from the constructor/initialiser has to operate > correctly on an object which at that point is not fully > constructed/initialised. So instead of having to write a method on a Foo > object, your template method has to operate on a partial Foo. The danger is > that you haven't clearly defined the partial Foo interface sufficiently and > the method tries to use other parts of the object which haven't yet been > set up.
In Python, if you try to use an uninitialized member you get an AttributeError; I really don't see too much inherent danger here. If you make a mistake, the language tells you and you fix it. C++ and Java are worse since accessing uninitialized variables is a silent mistake, so it makes sense to avoid that kind thing in those languages. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
