How to get class instances in Ruby?

Question

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

You could probably store a list of reference manually that you update from the constructor... but I'm curious why you would need to do that? — Locksfree, Jun 15 '11 at 23:33

score 24 · Answer 1 · edited Jan 07 '22 at 10:24

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.

score 20 · Accepted Answer · edited Feb 01 '14 at 22:02

20

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

edited Feb 01 '14 at 22:02

Chris Keele

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answered Jun 16 '11 at 00:08

steenslag

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if a instance got destoried, will this `@@instance_collector` get updated. – Vijay Apr 23 '15 at 06:19
@Vijay short answer is no, because there is no LOC removing the object from the array. – onebree Jan 05 '16 at 15:31

score 7 · Answer 3 · answered Jun 15 '11 at 23:33

7

Override new; keep count; expose property.

answered Jun 15 '11 at 23:33

alphazero

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+1 Short, sweet, to-the-point. – Kyle Sletten Jun 15 '11 at 23:39

How to get class instances in Ruby?

3 Answers3

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