isa pointer in objective-c

Question

From this reference:

When a new object is created, memory for it is allocated, and its instance variables are initialized. First among the object’s vari

Answer 1

On 64-bit environment, an object’s ISA field shouldn’t be accessed. The ISA field no longer holds a pointer. It includes some pointer data and uses the remaining bits to hold other runtime information. CLASS property or OBJECT_GETCLASS function can be used to read an isa field. OBJECT_SETCLASS can be used to write an isa field.

Ref: https://developer.apple.com/library/ios/documentation/General/Conceptual/CocoaTouch64BitGuide/ConvertingYourAppto64-Bit/ConvertingYourAppto64-Bit.html#//apple_ref/doc/uid/TP40013501-CH3-SW1