How to get class instances in Ruby? [duplicate]

This question already has answers here: How to find each instance of a class in Ruby (4 answers) 开发者_如何学Go Closed 7 years ago.

Say I have a class called Post that has many initiated instances (i.e. Post.new(:name => 'foo')).

Is there a way to retrieve all the instances of that class by calling something on it? I'm looking for something along the lines of Post.instances.all

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You can use ObjectSpace to retrieve all instantiated objects of a given class:

posts = []
ObjectSpace.each_object Post do |post|
  posts << post
end

This is almost certainly a bad idea, though - for example, it will also load Post instances that are still in memory from earlier requests that haven't been garbage-collected. There's probably a much better way to get at the posts you care about, but we'll need more information about what you're trying to do.

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Illustrating both alphazero's and PreciousBodilyFluids answers:

class Foo
  @@instance_collector = []
  def initialize
    @@instance_collector << self
    #other stuff
  end
  def self.all_offspring
    @@instance_collector
  end
end

a = Foo.new
b = Foo.new

p Foo.all_offspring  # => [#<Foo:0x886d67c>, #<Foo:0x886d668>]
p ObjectSpace.each_object(Foo).to_a # => [#<Foo:0x886d668>, #<Foo:0x886d67c>] #order is different

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Override new; keep count; expose property.