iOS instancetype or id ?

 

The id type simply says a method will return a reference to an object. It could be any object of any type.

The instancetype type says a method will return a reference to an object of the same type as the class on which this method was called. 

instancetype is a newer feature of Objective-C that basically adds type safety. In many cases, you will see no difference in an app (as you have mentioned). But there are times when instancetype is useful to avoid having to type cast when you call the method.

For example, imagine a class called SomeClass with a method like this:

+(id)createSomeClass
{
  return [[SomeClass alloc] init];
}

　　

Then imagine a subclass of SomeClass called SomeSubclass, that overrides that method like this:

+(id)createSomeClass
{
  return [[SomeSubclass alloc] init];
}

　　

Now, if you want to create a SomeSubclass, you would have to do this:

SomeSubclass *obj = (SomeSubclass*)[SomeSubclass createSomeClass];

However, if createSomeClass returned instancetype instead of id, then you could write this instead:

SomeSubclass *obj = [SomeSubclass createSomeClass];

You will see many people switching to instancetype for return values from any initializer or class creator methods (like the ones shown above). In fact, many of Apple's own APIs have been changed to use instancetype instead of id.

 

From: http://raywenderlich.com/forums/viewtopic.php?f=38&t=8959  , thanks !