Adding instantiated subclasses to array in superclass

Question

I'm trying to keep track of all instantiated subclass objects in an array in the super, so that I can call a method from super to iterate over them. I think I'm almost there but I can't figure out what I'm missing. Currently when I call super.my_array it's only returning an empty array, so there has to be something wrong with my initialize method. This is the abstracted version have I have so far:

class Klass
  attr_reader :my_array
  @@my_array = []
  def initialize
    @@my_array << self if super.class == Klass
  end
  def self.iterate_over_sub
    @@my_array.each { |x| x.sub_method }
  end
  def sub_method
    puts "#{self.class} is being called by super"
  end
end

Max · Accepted Answer · 2013-10-12 17:41:37Z

2

I'm going to provide an alternative answer to your question...

Honestly, I'd probably switch your approach on this a bit and create a separate class (that includes the Singleton module) with which your Klass registers, e.g.

class Klass
    def initialize
        KlassTracker.instance.track(self)
    end
end

require 'singleton'
class KlassTracker
    include Singleton
    def initialize
        @instances = []
    end
    def track(instance)
        @instances << []
    end
 end

Additionally, this by its very nature is going to leak memory like crazy, so I would recommend storing weak/soft references either using WeakRef or a library like ref (which I haven't used or seen before, but looks like what you'd want) and only tracking weak/soft references in your KlassTracker class.

Lastly, I'd be remiss if I didn't mention that what you're asking to do is, frankly, somewhat crazy. I don't know what you're trying to do, but there's probably a better approach.

answered Oct 12, 2013 at 17:41

Max

5,1214 gold badges32 silver badges47 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Max Over a year ago

Additionally, if you'd rather not have the runtime overhead and complexity of maintaining this list of instances, ObjectSpace.each_object(Klass) is another alternative.

Steven Spasbo Over a year ago

It's for a programming challenge that I'm stuck on, so performance isn't really a concern. I'm just trying to improve my ruby skills, but thanks for pointing me in the right direction!

Max Over a year ago

Ah, interesting...in general, I try to stay away from @@-variables (class variables). Compared to their Java counterparts, they're frighteningly hard to use predictably. Hence my tendency towards the Singleton mixin.

Edgars Jekabsons · Accepted Answer · 2013-10-12 17:45:59Z

Not sure what You are trying to achieve, but I see a few potential problems.

attr_reader defines an accessor on instance level, so it has nothing to do with class variable. Basically when You say attr_reader :my_array, it defines a method like this

def my_array
  @my_array
end

Secondly You will be better of checking type like this:

@@my_array << self if self.is_a?(Klass)

Here is an example that does what You need if I understood You correctly.

class Klass
  @@my_array = []

  def self.my_array
    @@my_array
  end

  def initialize
    @@my_array << self if self.is_a?(Klass)
  end
  def self.iterate_over_sub
    @@my_array.each { |x| x.sub_method }
  end
  def sub_method
    puts "#{self.class} is being called by super"
  end
end

class SubKlass < Klass
end

sk = SubKlass.new
#<SubKlass:0x007f8ecb861eb8>
Klass.my_array
#[#<SubKlass:0x007f8ecb861eb8>]

Stefan · Accepted Answer · 2013-10-12 18:08:06Z

0

To iterate over instances of a specific class, you can use ObjectSpace::each_object:

class Foo; end
class Bar < Foo; end
class Baz < Foo; end

Foo.new
Bar.new
Baz.new

ObjectSpace.each_object(Foo) { |x| p x }

Output:

#<Baz:0x007fc213859710>
#<Bar:0x007fc213859738>
#<Foo:0x007fc213859760>

Or as a class method:

class Foo
  def self.each_instance(&block)
    ObjectSpace.each_object(self, &block)
  end
end

Foo.each_instance { |x| p x }

edited Oct 12, 2013 at 18:08

answered Oct 12, 2013 at 17:51

Stefan

115k14 gold badges157 silver badges234 bronze badges

Comments

Cary Swoveland · Accepted Answer · 2013-10-13 14:31:54Z

0

Would this meet your needs?

class A
  @@instances = []
  def self.new
    a = super
    @@instances << a
    a
  end   
  def self.tryit
    @@instances.each {|e| e.test}
  end  
end

class B < A
  def test
    puts "hi"
  end        
end
b = B.new
c = B.new
b.test # => 'hi'
A.tryit # => 'hi\nhi'

edited Oct 13, 2013 at 14:31

answered Oct 13, 2013 at 3:49

Cary Swoveland

111k6 gold badges69 silver badges105 bronze badges

Collectives™ on Stack Overflow

Adding instantiated subclasses to array in superclass

4 Answers 4

3 Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

3 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related