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Peter Haworth > Class-Random-0.2 > Class::Random



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Module Version: 0.2   Source  


Class::Random - Random behaviour for instances


  package RandomSubclass;
  use Class::Random subclass => qw(A B);

  package ShufflePerMethod;
  use Class::Random shuffle => qw(C D);

  package ChoosePerMethod;
  use Class::Random choose => [qw(E F)],[qw(G H)];


This module allows you to create classes which randomly change their behaviour or implementation according to a specified behaviour. This is done simply by using the module, passing a parameter list which dictates the required behaviour. A number of behaviours are possible, determined by the first argument in the use Class::Random line:


The subclass behaviour is given a list of class names, and installs a new class method in the calling package. This method picks one of the class names given, and calls that class' new method. Note that if a new method is defined after this use statement, it will override the one defined by Class::Random.

This behaviour implements Damian Conway's idea of choosing a random implementation for each object created, in order to discourage users from directly accessing the object's internals, rather than using the interface like they are supposed to do.


The shuffle behaviour is given a list of class names, which are used to populate the calling package's @ISA array. It also installs an object in the first element of @ISA, which shuffles the rest of the array when accessed. This has the effect of causing each method called on the object to change the inheritance hierarchy.


The choose behaviour is like the shuffle behaviour, except that each element of the list is a complete @ISA array. This allows one of a number of different lists of base classes to be chosen with each method call.


The subclass method is the only remotely useful behaviour of this class, and even that's arguable.

Due to perl's normal sensible strategy of method caching, if the same method is called repeatedly under the choose or shuffle behaviours, without any others being called in between, it will always call the same method.


Damian Conway inspired the first version of this module (with the choose and shuffle behaviours), by wondering what would happen if you put something other than class names in a package's @ISA array. He immediately turned around and told us not to do that, but I'd already had this stupid idea.

Damian also came up with the idea for the subclass behaviour, only that was deliberate on his part. Still, I don't think he was expecting anyone to implement it.


Peter Haworth <>

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