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

Question

Is there any way in Ruby for a class to know how many instances of it exist and can it list them?

Here is a sample class:

class Project    attr_accessor :name, :tasks    def initialize(options)     @name = options[:name]     @tasks = options[:tasks]   end    def self.all     # return listing of project objects   end      def self.count           # return a count of existing projects     end   end 

Now I create project objects of this class:

options1 = {   name: 'Building house',   priority: 2,   tasks: [] }  options2 = {   name: 'Getting a loan from the Bank',   priority: 3,   tasks: [] }  @project1 = Project.new(options1) @project2 = Project.new(options2) 

What I would like is to have class methods like Project.all and Project.count to return a listing and count of current projects.

How do I do this?

Answer 1

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