why it doesn't work with 'id'?

[ksiedzulek]

Hi here is a code:

#import <Foundation/Foundation.h>


// --------------------------------------------------

@interface Tire : NSObject
@end // Tire


@implementation Tire

- (NSString *) description
{
    return (@"I am a tire. I last a while");
} // description

@end // Tire



// --------------------------------------------------

@interface Engine : NSObject
@end // Engine


@implementation Engine

- (NSString *) description
{
	return (@"I am an engine.  Vrooom!");
} // description*/

@end // Engine


// --------------------------------------------------

@interface Car : NSObject
{
	Engine *engine;
	Tire *tires[4];
	int d;
}
@property int d;
- (void) print;

@end // Car


@implementation Car
@synthesize d;
- (NSString *) description
{
return [NSString stringWithFormat:@"ID: %d",d];
}
- (id) init
{
	if (self = [super init]) {
		engine = [Engine new];
		
		tires[0] = [Tire new];
		tires[1] = [Tire new];
		tires[2] = [Tire new];
		tires[3] = [Tire new];
	}
	
	return (self);
	
} // init

- (void) print
{
	NSLog (@"%@", engine);
	
	NSLog (@"%@", tires[0]);
	NSLog (@"%@", tires[1]);
	NSLog (@"%@", tires[2]);
	NSLog (@"%@", tires[3]);
	
} // print

@end // Car


// --------------------------------------------------

int main (int argc, const char * argv[]) 
{
	Car *car; // car.d works
	//id car;		// car.d doesn't work..why?
	car = [Car new];
	
	car.d=5;// ????
	NSLog(@"car nalezy do: %@",[car class]);
	[car print];
	NSLog(@"%@",car);//
	
	return (0);
	
} // main

and question: why if I use [Car*car] (in main) it differs from using id car? when I use 'id car' and disable car.d=5 it works proper (why?) I check class by using [method class] and for 'id car' and Car*car it returns Car class...

[god0fgod]

From experience id doesn't work with certain things like the dot syntax for properties. Use the set method instead.

[smasher]

In order for dot syntax to work, the COMPILER must know the type of the object AT COMPILE TIME. If you declare the method as "Car *car", it knows how to create the methods calls. If you declare it "id car" then the compiler does not know the type of the object.

You can still access the property, but not with the dot syntax. Calling [car setD:5] should work fine either way.