How to List All Objects Created from a Class in Ruby

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

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

Ruby. How to collect all class elements from all class objects?

You need to make name_list a class variable

class Animal
  attr_accessor :name
  @@name_list = []

  def initialize
    @name = name
  end

 def set_name
   @name = gets
   puts "My name is #{@name}"
   @@name_list.push(@name.strip)
 end

 def self.show_all
   puts "List of your animals names: #{@@name_list}"
 end
end

How to find each instance of a class in Ruby

The solution is to use ObjectSpace.each_object method like

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

which produces

<Pokemon:0x0000010098aa70>
<Pokemon:0x00000100992158>
 => 2 

Details are discussed in the PickAxe book Chapter 25

return attributes from all objects of a class in ruby

The problem you have right now is that Player is your custom class. It does not respond to a class method each. Another issue is that the Player class has no knowledge of the instances created outside of it.

There's many ways to go about this. The way I would do this is to implement another class called Team like this

class Team
  def initialize(*players)
    @players = players
  end

  def player_numbers
    @players.map { |player| player.number }
  end
end

class Player
  attr_reader :number

  def initialize(name, number)
    @name = name
    @number = number
  end
end

guy1 = Player.new('Bill', 23)
guy2 = Player.new('jeff', 18)

team = Team.new(guy1, guy2)
team.player_numbers
#=> [23, 18]

Extract objects by their properties from list of class names in ruby

This sets @fruits with the list of Fruit Objects matching color: 'red' and @vegetables the list of Vegetable Objects matching color: 'red'

obj_list = ["Fruit", "Vegetable"]

obj_list.each do |c|
  list_name = "@#{c.downcase}s"
  list_objects = Object.const_get(c).where(color: 'red')
  instance_variable_set(list_name, list_objects)
end

@fruits #=> Fruit.where(color: 'red')
@vegetables #=> Vegetable.where(color: 'red')

hope this helps

Look up all descendants of a class in Ruby

Here is an example:

class Parent
  def self.descendants
    ObjectSpace.each_object(Class).select { |klass| klass < self }
  end
end

class Child < Parent
end

class GrandChild < Child
end

puts Parent.descendants
puts Child.descendants

puts Parent.descendants gives you:

GrandChild
Child

puts Child.descendants gives you:

GrandChild

How to list all methods for an object in Ruby?

The following will list the methods that the User class has that the base Object class does not have...

>> User.methods - Object.methods
=> ["field_types", "maximum", "create!", "active_connections", "to_dropdown",
    "content_columns", "su_pw?", "default_timezone", "encode_quoted_value", 
    "reloadable?", "update", "reset_sequence_name", "default_timezone=", 
    "validate_find_options", "find_on_conditions_without_deprecation", 
    "validates_size_of", "execute_simple_calculation", "attr_protected", 
    "reflections", "table_name_prefix", ...

Note that methods is a method for Classes and for Class instances.

Here's the methods that my User class has that are not in the ActiveRecord base class:

>> User.methods - ActiveRecord::Base.methods
=> ["field_types", "su_pw?", "set_login_attr", "create_user_and_conf_user", 
    "original_table_name", "field_type", "authenticate", "set_default_order",
    "id_name?", "id_name_column", "original_locking_column", "default_order",
    "subclass_associations",  ... 
# I ran the statements in the console.

Note that the methods created as a result of the (many) has_many relationships defined in the User class are not in the results of the methods call.

Added Note that :has_many does not add methods directly. Instead, the ActiveRecord machinery uses the Ruby method_missing and responds_to techniques to handle method calls on the fly. As a result, the methods are not listed in the methods method result.

How to list all the methods defined in top self Object in Ruby?

The closest I could find is to call private_methods on the main object, with false as argument

Returns the list of private methods accessible to obj. If the all
parameter is set to false, only those methods in the receiver will be
listed.

def foo
  "foo"
end

def bar
  "bar"
end

def baz
  "baz"
end

p private_methods(false)
# [:include, :using, :public, :private, :define_method, :DelegateClass, :foo, :bar, :baz]

If you omit the argument, you also get all the private methods defined in Kernel or BasicObject.

In order to refine the list further, you could select the methods defined for Object:

p private_methods(false).select{|m| method(m).owner == Object}
#=> [:DelegateClass, :foo, :bar, :baz]

Only :DelegateClass is left, because it is defined in the top-level scope, just like :foo, :bar and :baz.

Get list of a class' instance methods

You actually want TestClass.instance_methods, unless you're interested in what TestClass itself can do.

class TestClass
  def method1
  end

  def method2
  end

  def method3
  end
end

TestClass.methods.grep(/method1/) # => []
TestClass.instance_methods.grep(/method1/) # => ["method1"]
TestClass.methods.grep(/new/) # => ["new"]

Or you can call methods (not instance_methods) on the object:

test_object = TestClass.new
test_object.methods.grep(/method1/) # => ["method1"]

---

Related Topics