Memoization in ruby with nested methods

Copyclass Example
  def foo
    def foo
      @bar
    end
    bar = (1..10).inject(1, :*)
    puts "bar is #{bar}"
    @wibble = "wibble is #{bar / 30}"
    @bar = bar / 20
  end
end

example = Example.new
example.foo
bar is 3628800
=> 181440
example.foo 
=> 181440

The hard working method, the outer def foo is called only once, on the first invocation, afterward, the nested def foo overrides it and simply returning the @bar variable from the object. The nested def foo still accessing the same object.

Note that rubcop will yell at you with this memozation pattern.