gistfile1.rb

class Example
  def make_method(&block)
    line_no = __LINE__; method_defs = %{

      def dynamic_method
        #{block}.call(1)
      end

    }
    instance_eval method_defs, __FILE__, line_no
  end
end

example = Example.new

example.make_method do |n|
  n + 1
end

# expect to be 2
example.dynamic_method
#=> nil