How to get attributes that were defined through attr_reader or attr_accessor

Question

Suppose I have a class A

class A
  attr_accessor :x, :y

  def initialize(x,y)
    @x, @y = x, y
  end
end

How can I get x and y attributes without knowing how exactly they were named.

E.g.

a = A.new(5,10)
a.attributes # => [5, 10]

Answer 1

Use introspection, Luke!

class A
  attr_accessor :x, :y

  def initialize(*args)
    @x, @y = args
  end

  def attrs
    instance_variables.map{|ivar| instance_variable_get ivar}
  end
end

a = A.new(5,10)
a.x # => 5
a.y # => 10
a.attrs # => [5, 10]

Answer 2

While Sergio's answer helps, it will return all the instance variables, which if I understand correctly the OP's question, is not what is asked.

If you want to return only the 'attributes' that have e.g. a mutator, you have to do something slightly more complicated such as:

attrs = Hash.new
instance_variables.each do |var|
  str = var.to_s.gsub /^@/, ''
  if respond_to? "#{str}="
    attrs[str.to_sym] = instance_variable_get var
  end
end
attrs

This returns only the attributes declared with attr_accessor (or with a manually created mutator), and keep the internal instance variables hidden. You can do something similar if you want the ones declared with attr_reader.

Answer 3

class A
  ATTRIBUTES = [:x, :y]
  attr_accessor *ATTRIBUTES

  def initialize(x,y)
    @x, @y = x, y
  end

  def attributes
    ATTRIBUTES.map{|attribute| self.send(attribute) }
  end
end

This may not be the DRY-est, but if you are only concerned with doing this for one class (as opposed to a base class that everything inherits from), then this should work.