Module: SubclassAware

Defined in:
lib/classy/subclass_aware.rb

Overview

SubclassAware allows a class to know about all of the subclasses that descend from it in the inheritance tree.

Example

class Parent
  extend SubclassAware
end

class ChildA < Parent
end

class ChildB < Parent
end

Class ChildB1 < ChildB
end

Parent.subclasses   # => [ ChildA, ChildB, ChildB1 ]

Note

SubclassAware sets and maintains the class variable @@classy_subclasses on the extending class, so in the unlikely event that this class variable is already in use, unusual bugs may result.

Warning

This module defines an inherited() class method on the extending class to keep track of subclasses. Unfortunately, if this method is later re-defined, this inherited() method is lost and subclass tracking will break. In order to work around this, constructions like the following might be necessary:

class ChildC < Parent

  class << self; alias :old_inherited :inherited end
  def self.inherited(sub)
    old_inherited(sub)
    # ...your inherited() code...
  end

end

This is not considered an acceptable long-term state of affairs - hopefully in future versions of this module, this work around will not be necessary.

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.extended(klass) ⇒ Object

Instantiate a new Set of subclasses. Not intended to be called directly.



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# File 'lib/classy/subclass_aware.rb', line 53

def self.extended(klass)
  klass.class_exec { class_variable_set(:@@classy_subclasses, Set.new) }
end

Instance Method Details

#forget_subclasses ⇒ Object

Clear all info about known subclasses. This method is probably mainly useful for testing.



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# File 'lib/classy/subclass_aware.rb', line 78

def forget_subclasses
  class_exec { class_variable_get(:@@classy_subclasses).clear }
end

#inherited(sub) ⇒ Object

Add the inheriting class to the list of subclasses. Not intended to be called directly.

TODO: Find a way for self.inherited on the extended class not to blow this away without requiring a bunch of alias chain hoops to be jumped through, as described above.



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# File 'lib/classy/subclass_aware.rb', line 64

def inherited(sub)
  class_exec { class_variable_get(:@@classy_subclasses).add sub }
end

#subclasses ⇒ Object

Return an array of all known subclasses (and sub-subclasses, etc) of this class.



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# File 'lib/classy/subclass_aware.rb', line 71

def subclasses
  class_exec { class_variable_get(:@@classy_subclasses).to_a }
end