Re: Beginner Question Re: Memory Management
Re: Beginner Question Re: Memory Management
- Subject: Re: Beginner Question Re: Memory Management
- From: Quincey Morris <email@hidden>
- Date: Mon, 22 Jun 2009 22:29:44 -0700
On Jun 22, 2009, at 21:31, WT wrote:
So, to all beginners out there, whenever you define a property,
remember always to refer to it, in its own class, by self.property -
at least when setting its value. It may be ok (depending on what
you're doing) to refer to it simply by property when *getting* its
value, but if the property is backed by an instance variable that is
an object (rather than a scalar type), it's *essential* that you
refer to it by prepending self when *setting* its value, or you'll
not be doing the memory management that you think you're doing.
I understand what you're trying to say here, but I'd urge you *never*
to describe it in these terms.
You say, explicitly, that it's a question of use the the correct way
(out of a choice of 2 ways) to refer to a property. But that's not so.
There's *one* way to refer to a property, and *one* way to refer to an
instance variable. The fact that they may have similar names is purely
an accident. (Well, not an accident, generally, but a convenience.)
I'd say it's really, really, really important for beginners to realize
that properties and the instance variables that back them are
different, syntactically and semantically. Outside a class
implementation, the property is the only thing that's available (or
should be, since making instance variables public is usually a Bad
Idea), so clients of the class don't have to think about it. Inside a
class implementation, however, you need to decide *every time you
refer to a value* whether you mean the property value or the instance
variable value. You need to decide that even when you *know* that the
two values are currently the same, because in a future piece of the
implementation you may break the congruence, but you don't want to
break the existing code if you can help it.
It's not even about memory management. There's often memory management
involved when using a property's accessors, but there may also be
memory management involved when dealing with an instance variable in
other contexts.
FWIW.
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