I have re-written the Accessors chapter of "Cocoa Design Patterns" several
times because of controversy over whether accessors should, can, must or must
not be used in initializers and dealloc. The bottom line is that accessors are
the only way to set synthesized instance variables to nil in the modern (64bit)
Objective-C runtime. Furthermore, you must use accessor for properties that
are not backed by instance variables e.g. properties stored in axillary
dictionaries etc. Accessor must be used in initializers and dealloc in at
least some cases. I like consistency, and I use accessors within initailizers
and dealloc. An excerpt of my current recommendation (especially a note:)
follows:
Confining Memory Management to Accessors
If the Accessors pattern is -[if supportFields]>consistently applied, almost
all memory
management for objects can be confined to accessors. When initializing object
instances, use a set accessor to set the value of each object property. For
example, the following implementation of -(id)initWithStringValue:(NSString
*)aValue method uses an accessor to store the string value
rather than making a direct assignment to an instance variable:
-
(id)initWithStringValue:(NSString *)aValue
{
self = [super init];
[self setStringValue:aValue]; // set the
initial value of the property
return self;
}
The process of initializing instances
is described in Chapter 3, "Two-Stage Creation."
The -dealloc method can indirectly release referenced objects
using the set accessors and avoid memory management code in its
implementation as
follows:
- (void)dealloc
{
[self setStringValue:nil]; // any previous string value is released
[super dealloc];
}
Note
Some programmers have historically avoided using accessors within
initializer methods and -dealloc
because a subclass may override inherited accessors to cause side effects.
Using the overridden accessors within the superclass’s initializer might invoke
side effects before the subclass instance is fully initialized. Similarly,
accessors called from within the
superclass’s -dealloc may cause side
effects in partially deallocated instances. However, there is no practical
alternative to using accessors when you use synthesized instance variables with
the modern Objective-C 2.0 runtime or use properties that are not implemented
as instance variables. In such cases,
accessors provide the only way to initialize the properties or set the
properties to nil.
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