superclass - What is the proper way to lazy initialize an abstract property in Objective-C -

in super class:

@property (strong, nonatomic) foo *foo; 

in sub class:

- (foo *) foo {      if(!super.foo) super.foo = [[foo alloc] init];      return super.foo; } 

does make sense? idea have abstract properties?

strictly speaking, there no "abstract class" or "abstract property" in objective-c, see example thread creating abstract class in objective-c overview.

your approach not optimal, because requires superclass implements foo , setfoo:, contradicts idea of "abstractness".

a better solution define "dynamic property" in superclass:

@interface superclass : nsobject @property (strong, nonatomic) foo *foo; @end  @implementation superclass @dynamic foo; @end 

and explicitly synthesize in subclass:

@interface subclass : superclass @end  @implementation subclass @synthesize foo = _foo; @end 

now can access foo on subclass object, on superclass object cause runtime exception.

for lazy initialization, can use usual pattern, without "super-tricks":

- (foo *) foo {     if(!_foo) _foo = [[foo alloc] init];     return _foo; } 

an alternative approach (also mentioned in above thread) use "protocol" instead of common superclass:

@protocol hasfoo <nsobject> - (foo *)foo; @end  @interface myclass : nsobject<hasfoo> @property(strong, nonatomic) foo *foo; @end  @implementation subclass - (foo *) foo {     if(!_foo) _foo = [[foo alloc] init];     return _foo; } @end