Performance in Objective-C

Printer Data Matrix 2d barcode in Objective-C Performance

Language performance and benchmark wars are infamous, but few would argue that C is the fastest high-level computer language available today. There are many that claim to be nearly as fast, but it s almost impossible to exceed C s performance without resorting to hand-coded optimizations or just trickery. It s no wonder that almost all interpreters are written in C or C++ and that includes Java s own virtual machine. Because Objective-C is also C, you can optimize your application right to the limits of the hardware. It s easy to start with a simple object-based design. If performance analysis shows that the solution isn t fast enough, it can be optimized with snippets of C. Or the code can be rewritten entirely in C. If that s not fast enough, the C compiler gives you direct access to the operating system kernel, graphics coprocessors, vector unit instructions, and even raw machine code. If your goal is to create the fastest possible application, Objective-C will not get in the way. Programming in Objective-C also means you have direct access to the vast library of C APIs. The POSIX C functions available today represent some of the most mature, stable, and secure code in the industry.

Objective-C is often described as a dynamic language. That s a difficult term to define. After all, every program is dynamic in some form. The term does describe some aspects of the Objective-C language itself, but most often refers to the design patterns embraced by Objective-C developers. The Objective-C language is more dynamic than languages like Java and C++. In Java, the variables and methods you define for a class are exactly those at runtime. In Objective-C, class definitions are more malleable. Other objects and frameworks, which you may or may not have developed, can augment your classes and objects with new capabilities. Conversely, you can augment other classes even system classes with new functionality. Another intriguing feature of Objective-C is the ability of the runtime system to modify the behavior of an object on the fly. A particularly dramatic example of this is in the observer pattern. In Java, an observable object is responsible for maintaining a set of listener objects and notifying them of

changes to its properties. In Objective-C when an object wants to observe the property of another object, it makes a request to the Key-Value Observing framework. This framework spontaneously subclasses the target object, wrapping its setter method with code to notify interested observers of changes. This remarkable ability means that every object is observable without writing a single line of code or requiring you to do any design work ahead of time. The contrast between Java and Objective-C in broad strokes is shown in Listing 1-2. The Key-Value Observing framework does all the work of maintaining the set of observers for each object and sending the requested notifications. All you have to do is declare the property and request to be notified of changes to it. Listing 1-2. Observer Pattern in Java and Objective-C public interface SecurityGateListener { void gateStateChanged( SecurityGate gate ); } public class SecurityGate { private HashSet listeners; private boolean open; public void addListener( SecurityGateListener listener ) { listeners.add(listener); } public void removeListener( SecurityGateListener listener ) { listeners.remove(listener); } private void fireStateChange( ) { for ( SecurityGateListener listener: listeners ) listener.gateStateChanged(this); } public boolean getOpen( ) { return open; } public void setOpen( boolean open ) { if (this.open!=open) { this.open = open; fireStateChange(); } } }

class SecurityManager implements SecurityGateListener { SecurityGate gate; SecurityManager( ) { gate = gate.addListener(this); } public void gateStateChanged( SecurityGate gate ) { // security gate changed ... } } @interface SecurityGate : NSObject { BOOL open; } @property BOOL open; @end @implementation SecurityManager - (id)init { if ( (self=[super init])!=nil ) { gate = [gate addObserver:self forKeyPath:@"open" options:0 context:NULL]; } return self; } - (void)observeValueForKeyPath:(NSString*)keyPath ofObject:(id)object change:(NSDictionary*)change context:(void*)context { if (object==gate) { // security gate changed... } } @end The dynamic nature of Objective-C applications often stems more from the design patterns embraced by developers than anything inherent in the language although Objective-C does make those patterns easier to adopt. Take the simple example of implementing copy and paste methods for a custom view object. The Cocoa framework defines something called the responder chain. It starts with the view object that currently has the user s focus, say some selected text or graphic displayed by your custom view object. The chain consists of that object, the view object that contains it, the window that