When alloc is called, it (as any other message send) first gets transformed (by the compiler) into one of the objc_msgSend* functions. This function will get the class structure pointer as its first argument, and @selector(alloc) as its second.
之后,斜体(sgSend)审视了<条码>+[等级]的相应执行方法,一般而言,这种方法并非压倒一切(在概念上,先入门......),因此,一般而言是+[所有物体]。 一切可能都只是叫+[NSObject alloc 具体如下:
1) It finds the class istance size (probably via class_getInstanceSize())
2) It allocates memory, most likely using the class_createInstance() function. This function clears the allocated memory to zeroes (that s why, as the specs say, all your ivars are explicitly initialized to 0 on startup), then sets the newliy created object s isa pointer to the class structure itself.
3) The allocWithZone: methods returns the fresh object pointer to alloc
4) alloc returns the object pointer to the sender, most likely it will run into [Class initWith...:].
Hope this helps. Also, apart from the Obj-C runtime docs, don t forget to check the GNUstep NSObject implementations. That s a logic and possible way how the GNU people implemented it and how Apple might have implemented it.
