property and synthesize directives in Objective C 2.0

@property directive is to declare a property

@interface Test : NSObject {
}
@property (readwrite,assign) int var1
@property (readonly,assign) int var2
@property (getter=foo, setter=foo1:) int var3
@end

readwrite attribute (default) tells the compiler to generate both getter and setter accessors

readonly attribute tells the compiler not to generate a setter accessor

assign attribute to implement set-by-assignment (i.e. generate setter and simply assigns a value to the instance variable)

-(void) setVar1:(NSString *)s
{
var1 = s;
}


copy attribute to implement set-by-copy (usually for mutable object)

-(void) setVar1:(NSString *)s
{
[var1 release];
var1 = [s copy];
}


retain attribute to implement set-by-retainment (i.e. generate setter and retain a value before assignment)

-(void) setVar1:(NSString *)s
{
[s retain];
[var1 release];
var1 = s;
}


@synthesize directive is to make the compiler generate accessors

@implementation Test
@synthesize var1;
@synthesize var2;
@dynamic var3;
@end

By Default, these messages are named var1 and setVar1 where var1 is the name of the variable

dynamic attribute tells the compiler not to generate any accessor messages

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Here is a good guideline for memory management in Cocoa
http://oreilly.com/pub/a/mac/excerpt/Cocoa_ch04/index.html

Retention Count rules

• Within a given block, the use of -copy, -alloc and -retain should equal the use of -release and -autorelease.
  
• Objects created using convenience constructors (e.g. NSString's stringWithString) are considered autoreleased.
  
• Implement a -dealloc method to release the instance variables you own
  

• retain increases the reference count of an object by 1
  
• release decreases the reference count of an object by 1
  
• autorelease decreases the reference count of an object by 1 at some stage in the future
  
• alloc allocates memory for an object, and returns it with retain count of 1
  
• copy makes a copy of an object, and returns it with retain count of 1