gistfile1.rb

class Foo
end

class Flibby
  def make_method( _method_name )
    puts _method_name
    Foo.class_eval do
      puts _method_name
      class << self
        define_method _method_name do
          puts "yay"
        end
      end
    end
  end
end

Flibby.new.make_method "wibble"

[ 22:50 ][ dml@shifter ] % ruby ~/test.rb
wibble
wibble
/home/dml/1.rb:10:in `make_method': undefined local variable or method `_method_name' for #<Class:Foo> (NameError)
        from /home/dml/1.rb:7:in `class_eval'
        from /home/dml/1.rb:7:in `make_method'
        from /home/dml/1.rb:18
zsh: exit 1     ruby ~/1.rb