A mixin implementing the Factory design pattern via Ruby meta-programming.
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README.rdoc

Welcome to the Factory!

Overview

The Factory mixin provides a robust Factory implementation. Overrides are automatically registered upon sub-classing. Manual override and disables are available if auto-registration does not result in the desired factory overrides. Manual overrides are available at the class and global granularities. Method arguments can be passed in as strings or symbols so that overrides can be set even before classes have been defined.

Usage

Using the Factory

The Factory module should be included in the classes which you want to provide factory overrides.

class ParentClass
  include Factory
  def initialize arg=nil
    @arg = arg
  end
end

Inheriting from this class will automatically register the sub-class as the override of the parent class.

class Child1 < ParentClass
end

Sub-classes need not include Factory though doing so should not hurt anything. The create class method is implemeted by the mixin for the parent class and all sub-classes. Constructor arguments can be passed similarly through create.

ParentClass.create('hello') # Returns an object of type Child1

Subsequent sub-classing updates the factory overrides.

class Child2 < Child1
end

ParentClass.create # Returns an object of type Child2
Child1.create # Returns an object of type Child2
ParentClass.new # Works normally. Returns an object of type ParentClass.

class Child3 < ParentClass
end

ParentClass.create # Returns an object of type Child3
Child1.create # Returns an object of type Child2 since Child3 is not a decendent.

Manual Factory Overrides

If the resulting factory overrides are not what is desired, they can be manually overriden. The methods that are discussed in the section takes arguments which are the class constants

Factory.global_disable_override Child3

or as a symbol (strings are also accepted).

Factory.global_disable_override :Child3

This allows overrides to be used even before a class is defined.

Factory Override Disable

Continuing from the above example ParentClass has a factory override of Child3 since it was the last sub-class to inherit from it. If the intention is to have Child2 be the factory override there are several ways this can be accomplished. To disable a class from overriding a particular class either of the following can be used.

Factory.disable_override ParentClass, Child3
ParentClass.create # Returns an object of type Child2

or,

ParentClass.disable_factory_override Child3
ParentClass.create # Returns an object of type Child2

Since the disable is with respect to a specific ancestor, other ancestors are uneffected.

Factory Override Enable

Another way of manually configuring overrides is through enabling an override. This can also be used to cancel an existing class specific factory disable override.

Factory.enable_override ParentClass, Child3
ParentClass.create # Returns an object of type Child3

The last override enable takes presedence.

Factory.enable_override ParentClass, Child2
ParentClass.create # Returns an object of type Child2

or,

ParentClass.enable_override Child2
ParentClass.create # Returns an object of type Child2

Subsequent calls of the disable override methods will cancel the previous enable overrides on the same types.

Global Factory Override Methods

To disable a class from overriding any classes use the following,

Factory.global_disable_override Child3

To cancel the disable override,

Factory.remove_global_disable_override Child3