OO style advice

[Alan Gauld]

On Mon, 16 Feb 2004 14:54:31 -0000, "DomF"
<fidtz at clara#spam#.co.uk> wrote:
> I am passing in a clock object to the board in __init__ to achieve this.
> However, means that the clock object can be changed via the board object and
> the clock object. Is this good style or should I be designing in a totally
> different way?

In OO objects communicate via messages. Thus think about the
messages that can be sent to the clock. Do not think about the
data inside the clock, that should be treated as private (even
though Python does not enforce this).

Now you have a single clock object but referenced both inside and
outside the board. Is that really what you want or do you want
the oard to have its own clock instance internally? If it is a
single object then its perfectly reasonable that both internal
and external objects can send it messages. If its an internal
object then only the board can conceptually see it.
If you need to initialise the internal clock you may want to take
a time parameter to the board and use that to set the clock
initial values, rather than passing a functioning clock object as
the parameter.

Also as somebody else said you may want to use multiple clock
objects...

> I previously had them separate but that led to lots of ugly board.time1 =
> clock.time1 statements.

Rather than access the data I'd provide a method, say
synchronise?

board.synchronise(myClock)

Which internally sets the board clock to the same time as the
parameter clock, something like:

def synchronise(self, aClock):
    self.clock.setTime(aClock.time())

Whether you think that looks any less ugly than the assignments
you had is a moot point!

Alan G.
Author of the Learn to Program website
http://www.freenetpages.co.uk/hp/alan.gauld