#ruby-201910282116.rb

module AccessorA
  def a
    puts "getter a called, current value: #{@a.inspect}"
    @a
  end
  
  def a=(a)
    puts "setter a called, current value: #{@a.inspect}, new value: #{a.inspect}"
    @a = a
  end
end

obj = Object.new
obj.extend(AccessorA)

obj.a &&= 1
# getter a called, current value: nil
#=> nil

obj.a = 2
# setter a called, current value: nil, new value: 2
#=> 2

obj.a &&= 3
# getter a called, current value: 2
# setter a called, current value: 2, new value: 3
#=> 3