What is #import?
It’s a C preprocessor construct to avoid multiple inclusions of the same file.
#import <Object.h>
is an alternative to:
#include <Object.h>
where the .h file is protected itself against multiple inclusions:
#ifndef _OBJECT_H_ … #define _OBJECT_H_ #endif
What is id?
It’s a generic C type that Objective-C uses for an arbitrary object. For example, a static function that takes one object as argument and returns an object, could be declared as:
static id myfunction(id argument) { ... } What is an IMP?
It’s the C type of a method implementation pointer, a function pointer to the function that implements an Objective-C method. It is defined to return id and takes two hidden arguments, self and _cmd:
typedef id (*IMP)(id self,SEL _cmd,...);
How do I get an IMP given a SEL?
This can be done by sending a methodFor: message:
IMP myImp = [myObject methodFor:mySel];
How can I link a C++ library into an Objective-C program?
You have two options: either use the Apple compiler or use the POC. The former accepts a mix of C++ and Objective-C syntax (called Objective-C++), the latter compiles Objective-C into C and then compiles the intermediate code with a C++ compiler.
How do I make a static method?
Methods are always implemented in Objective-C as static functions. The only way to obtain the IMP (implementation pointer) of a method is through the runtime (via methodFor: and friends) because the function itself is static to the file that implements the method.
How do I include X Intrinsics headers into an Objective-C file?
To avoid a conflict between Objective-C’s Object and the X11/Object, do the following:
#include <Object.h> #define Object XtObject #include <X11/Intrinsic.h> #include <X11/IntrinsicP.h> #undef Object
How do I allocate an object on the stack?
To allocate an instance of ‘MyClass’ on the stack:
MyClass aClass = [MyClass new];
What’s the class of a constant string?
It’s an NXConstantString.
NXConstantString *myString = @"my string";