View an objects Instance Variables

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It is possible to query an object about its instance variables using instance_variables, instance_variable_defined?, and instance_variable_get, and modify them using instance_variable_set and remove_instance_variable:

class Foo
  attr_reader :bar
  def initialize
    @bar = 42
  end
end
f = Foo.new
f.instance_variables                #=> [:@bar]
f.instance_variable_defined?(:@baz) #=> false
f.instance_variable_defined?(:@bar) #=> true
f.instance_variable_get(:@bar)      #=> 42
f.instance_variable_set(:@bar, 17)   #=> 17
f.bar                               #=> 17
f.remove_instance_variable(:@bar)   #=> 17
f.bar                               #=> nil
f.instance_variables                #=> []

The names of instance variables include the @ symbol. You will get an error if you omit it:

f.instance_variable_defined?(:jim)
#=> NameError: `jim' is not allowed as an instance variable name

Found a mistake? Have a question or improvement idea? Let me know.

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