Using attr_readers, attr_writers, and attr_accessors

named_wombat.rb

# attr_reader/writers/accessors are handy shortcuts for creating
# getter and setter methods. That's all they're for.

# An attr_reader creates a getter method. For example, the following
# two classes have identical effects:

class NamedWombat
  attr_reader :name

  def initialize(name)
    @name = name
  end
end

class NamedWombat
  def name
    @name
  end

  def initialize(name)
    @name = name
  end
end

# In either case we can define a wombat and get its name.

elmer = NamedWombat.new("Elmer")
elmer.name # => "Elmer"

# An attr_writer creates a setter method. Using an attr_accessor is
# equivalent to using both an attr_reader and an attr_writer. So the
# following three classes have identical effects:

class RenamableWombat
  attr_accessor :name

  def initialize(name)
    @name = name
  end
end

class RenamableWombat
  attr_reader :name
  attr_writer :name

  def initialize(name)
    @name = name
  end
end

class RenamableWombat
  def name
    @name
  end

  def name=(new_name)
    @name = new_name
  end

  def initialize(name)
    @name = name
  end
end

# Any of those three definitions would let us define and acces a
# wombat as follows:

my_wombat = RenamableWombat.new("Elmer")
my_wombat.name # => "Elmer"
my_wombat.name = "Lucky Eddy"
my_wombat.name # => "Lucky Eddy"

# attr_readers, attr_writers, and attr_attributes can all be defined
# privately. So, for example, the following two class definitions are
# equivalent:

class AnonymousWombat
  def initialize(name)
    @name = name
  end

  private

  attr_reader :name
end

class AnonymousWombat
  def initialize(name)
    @name = name
  end

  private

  def name
    @name
  end
end

# When we try to call name on an AnonymousWombat, Ruby rightly
# complains that we're trying to call a private method:

secret_wombat = AnonymousWombat.new("Elmer")
secret_wombat.name # =>
# ~> -:103:in `<main>': private method `name' called for #<AnonymousWombat:0x007fe54186b1d0 @name="Elmer"> (NoMethodError)