How do I list all objects created from a class in Ruby? [duplicate]

Answer 1

One way to do is to keep track of it as and when you create new instances.

class Project

    @@count = 0
    @@instances = []

    def initialize(options)
           @@count += 1
           @@instances << self
    end

    def self.all
        @@instances.inspect
    end

    def self.count
        @@count
    end

end

If you want to use ObjectSpace, then its

def self.count
    ObjectSpace.each_object(self).count
end

def self.all
    ObjectSpace.each_object(self).to_a
end

Answer 2

You can use the ObjectSpace module to do this, specifically the each_object method.

ObjectSpace.each_object(Project).count

For completeness, here's how you would use that in your class (hat tip to sawa)

class Project
  # ...

  def self.all
    ObjectSpace.each_object(self).to_a
  end

  def self.count
    all.count
  end
end

Answer 3

class Project
    def self.all; ObjectSpace.each_object(self).to_a end
    def self.count; all.length end
end

Answer 4

Maybe this will work:

class Project
  class << self; attr_accessor :instances; end

  attr_accessor :name, :tasks

  def initialize(options)
    @name = options[:name]
    @tasks = options[:tasks]

    self.class.instances ||= Array.new
    self.class.instances << self
  end

  def self.all
    # return listing of project objects
    instances ? instances.dup : []
  end

  def self.count
    # return a count of existing projects
    instances ? instances.count : 0 
  end

  def destroy
    self.class.instances.delete(self)
  end
end

But you will have to manually destroy these objects. Maybe other solution can be build based on ObjectSpace module.