With:
book._title = ‘foo’
I can modify the property from the outside anyway … right?

class Book
attr_accessor :title
end

which gives you

book = Book.new
book.title = ‘rftw’
puts book.title # => “rftw”

> Don’t use double underscore prefixes. Ever.
Changed. Thanks for the tip.

> with Python 2.4 or more recent, you can use the ‘property’ function
Nice :)

>>> class Foo(object):
….def __init__(self, some_value):
……..self.some_value = some_value

>>> foo = Foo(42)
>>> foo.some_value
42
>>> foo.some_value = 5
>>> foo.some_value
5
>>> class Foo(object):
….def __init__(self, some_value):
……..self._some_value = some_value
….@property
….def some_value(self):
……..return self._some_value

>>> foo = Foo(42)
>>> foo.some_value
42
>>> foo.some_value = 5

Traceback (most recent call last):
..File “”, line 1, in
….foo.some_value = 5
AttributeError: can’t set attribute
>>>

* Don’t use double underscore prefixes. Ever. It’s bad style. A single underscore is all you need, don’t go for more, name mangling wasn’t introduced to create pseudo-private members.

* While I realize it’s for the sake of the example, don’t create empty properties (the ones you’ve created here) either, they create indirection and make the code slower and more complex for no gain. You can transparently introduce properties later if and when you need them.

the __call() function checks against a list of available variables, so principles of data hiding can be adhered to where required.

this method has the added advantage of being able to overwrite this default behaviour by adding in any other function, as in the requirement above of adding in a new filter/modifier on a property.

the __call() function can be seen at http://pastebin.com/f28429455. the code is ripped out of my current DataObject class and has some additional code to allow all objects to return the objects ID and load status.