|P is for Practical|
Modification of @ISA at run timeby jkeenan1 (Deacon)
|on Sep 01, 2005 at 03:45 UTC||Need Help??|
jkeenan1 has asked for the
wisdom of the Perl Monks concerning the following question:
In Chapter 16: Class Hierarchies, subsection Inheritance (bottom p. 360) of Perl Best Practices, TheDamian recommends defining "a class's hierarchy declaratively at compile time, using the standard use base pragma. He argues that
"this approach discourages messing about with class hierarchies at run time, by reassigning @ISA. The temptation to modify @ISA at run time is usually a sign that your class might be better implemented as a factory, a fašade, or with some other meta-object technique. (Emphasis added.)
Atypically, Damian doesn't provide an example of the code that would implement one of those other techniques. Not being experienced in design patterns, I'm somewhat at sea here. So I'm wondering if someone could provide a simple example of, say, the alternative to something like this:
And later, at run time ...
... called because, under certain unusual conditions, I want to make sure that the inheritance mechanism finds an Astrological::Data method (say, get_sunrise_time) before it finds Solar::Data::get_sunrise_time().
What would the alternative approach look like in code? Why, particularly in a simple case, would it be superior?
Thank you very much.