Pro Multithreading and Memory Management for IOS and OS X: With ARC, Grand Central Dispatch and Blocks by Kazuki Sakamoto & Tomohiko Furumoto

Author:Kazuki Sakamoto & Tomohiko Furumoto [Sakamoto, Kazuki & Furumoto, Tomohiko]
Language: eng
Format: epub
Tags: Computers, Programming, Apple Programming, Object Oriented
ISBN: 9781430241164
Publisher: Apress
Published: 2012-04-25T04:00:00+00:00

By the C++ compiler, it is converted to a source code calling the C function as follows.

struct MyClass cls;

__ZN7MyClass6methodEi(&cls, 10);

"this" is an instance of MyClass class (struct) itself. In addition, let's check an

instance method in Objective-C.

- (void) method:(int)arg

{

NSLog(@"%p %d\n", self, arg);

}

The same as for C++ methods, the Objective-C compiler converts the method to a C

function.

void _I_MyObject_method_(struct MyObject *self, SEL _cmd, int arg)

{

NSLog(@"%p %d\n", self, arg);

}

And the same as “this” in C++, “self” is passed as the first argument. Let’s see its caller as well.

MyObject *obj = [[MyObject alloc] init];

[obj method:10];

Using “-rewrite-objc option” for clang, we can see how it is converted:

MyObject *obj = objc_msgSend(

objc_getClass("MyObject"), sel_registerName("alloc"));

obj = objc_msgSend(obj, sel_registerName("init"));

objc_msgSend(obj, sel_registerName("method:"), 10);

The objc_msgSend function searches a pointer of the _I_MyObject_method_ function by the object and the method name. After that, it calls the function pointer, and the first argument “obj” is passed to the _I_MyObject_method_ function as its first argument “self”. As in C++, “self” is the object of the MyObject class itself.

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