From: Hal Fulton <hal9000@...>
Date: 2006-01-05T12:29:18+09:00
Subject: Re: Can't change the value of self

Henrik Martensson wrote:
> Immutable classes are less prone to bugs than mutable classes. This is
> because they have a single state. They are also thread safe. 
> 
> It is good practise to favor immutability when there are no compelling
> reasons for making a class mutable.
> 
> A Time object represents an instance in time. Making it mutable could
> easily get confusing. Consider:
> 
> time = MutableTime.at(946702800)
> rocket.launch_time = time
> ...
> time.change(946701565) # Changes the launch time of the rocket
> 
> 
> The launch time of the rocket can be changed without setting the
> launch_time property explicitly. This is a potential source of bugs.


Thanks, Henrik. That's a great discussion and a great example.


Hal