MyClass.h

@interface MyClass : NSObject

@property (nonatomic, strong) NSComplexThing * myThing;

@end

MyClass.mm

#import "MyClass.h"

#define LAZY_GETTER(TYPE, NAME) \
- (TYPE)NAME { return (_##NAME = (_##NAME) ?: [self _lazyLoad_##NAME]); } \
- (TYPE)_lazyLoad_##NAME

@implementation MyClass

LAZY_GETTER(NSComplexThing *, myThing)
{
  NSComplexThing * thing = [[NSComplexThing alloc] init];
  thing.stuff = // .. do your super complex initializer here

  return thing;
}

@end