Re: Objective-C questions
Re: Objective-C questions
- Subject: Re: Objective-C questions
- From: Alastair Houghton <email@hidden>
- Date: Thu, 23 Aug 2007 11:20:09 +0100
On 22 Aug 2007, at 17:30, Shawn Erickson wrote:
On 8/22/07, Daniel Child <email@hidden> wrote:
Your list of advice brings up host of questions. Specifically, (in
reference to your points)
#1 (always use accessors)
Would you recommend using accessors even for primitive instance
variables (int, BOOL, etc.), where there is no need to retain, copy,
etc.
The fact that you store them internally as a primitive instance
variable currently doesn't mean that in the future you may store them
a different way. If you provide accessors as the interface to get at
the data then you have more freedom to change your implementation in
the future without affecting client code.
Indeed, though it's worth saying that people differ on whether they use
accessors or not in implementations, at least for variables that have
been defined by the subclass they're implementing.
There is a trade-off between performance and maintainability/
extendability;
sometimes you don't need the latter but need the former and vice-versa.
#5 - #6 (use immutable objects whenever possible) Why the emphasis on
immutable objects? Simply because they are more efficient?
They usually will be more efficient when accessed, etc. but obviously
they wont be more efficient if they need to be modified.
They also tend to be thread-safe, whereas mutable objects generally
aren't.
The important thing to consider is what you care about when you take
ownership, ask yourself... Do I want the same object state going
forward in time as when I first got the object (if so copy it, if not
retain it).
A good example of this is that you often find you want to -copy NSString
arguments e.g. to setters and/or initialiser methods.
#8 (use a class accessor for class globals etc.)
???? I have no idea how to do 8. I expect to need plenty of class-
related constants. For example, my singleton class (a string parser
to parse input into syllables) has a list of values against which
input text is to be checked. I stored those values in an NSSet which
is one of the instance variables. You are recommending something
else?
In Objective-C, sometimes people don't bother creating explicit
singletons
where they might be more inclined to in some other OO languages.
The reason is that classes themselves are already singleton objects, and
often a singleton is used because it's there to manage a group of
objects
of a particular class. Additionally, ObjC allows you to override class
methods, which isn't the case in some other languages (C++, for
instance).
In such cases, the variables that would have been instance variables of
the singleton generally become static variables in the ObjC file
containing
the implementation of the class. You might then have class method
accessors
to change them.
To give a concrete example, take a look at NSBezierPath. It has a
load of
accessors for the default winding rule, line cap and join styles, line
width, etcetera, not to mention a number of special-purpose convenience
constructors. As a result, in some other languages, it *might* have
been
implemented as a BezierPathFactory singleton with a separate BezierPath
class.
The more conventional singleton pattern is definitely still used though;
e.g. in NSFontManager or NSWorkspace.
Kind regards,
Alastair.
p.s. Please don't send messages without a subject line to the list.
This
being a high-volume list, not everyone has time to read and/or reply to
every message; nor is everyone interested in every subject brought up.
Using the subject line helps with that a lot.
--
http://alastairs-place.net
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| References: | |
| | >Re: (From: Daniel Child <email@hidden>) |
| | >Re: (From: "Shawn Erickson" <email@hidden>) |