define_method_and_block.rb

define_method :create do |field, &block|
  define_method "#{field}=" do |arg|
    instance_variable_set(:"@#{field}", arg)
  end
  define_method "#{field}" do
    puts instance_exec(&block)
    instance_variable_get(:"@#{field}")
  end
end
A = Class.new do
  create('a'){ hello }
  def hello
    "Hello!"
  end
end

o = A.new
o.a