moep.rb

# That is _NOT_ how you do it. you define it on the class generally (all new instances will have them) instead of just the instance.

def accept_virtual *fields
  fields.each {|f| self.class.__send__(:attr_accessor, f) }
end

# That is a way but it's dirty :)
def accept_virtual *fields
  metaclass = class << self; self; end
  fields.each do |f|
    metaclass.__send__(:define_method, :"#{f}") { instance_variable_get(:"@#{f}") }
    metaclass.__send__(:define_method, :"#{f}=") {|v| instance_variable_set(:"@#{f}", v) }
  end
end

# That's also a thing
foo = "bar"

foo.bar? # NoMethodError: undefined method `bar?' for "bar":String

def foo.bar?
  self == "bar"
end

foo.bar? # true
foo.replace("baz")
foo.bar? # false

"".bar? # NoMethodError: undefined method `bar?' for "":String