Q:  How do you store and access elements in the Storage class?

A:  Although Storage's instance variables permit you to access the data directly, this approach is discouraged.   Instead, use the Storage object's methods (such as addElement: and elementAt:) to store and access the elements.  

Following is a code snippet that creates an empty Storage object, adds new elements to it, and then references them.  The type-specific code is #defined for clarity.  Note that the elements need to be added and referenced as pointers.

	#import <objc/Storage.h>

	@interface SomeObject:Object
	@end
	@implementation SomeObject

	#if 1
	#define TYPE char *
	#define PRINT(var1, var2)  printf("first = %s second = %s\n", var1, var2);
	#define VAL1 ("hello")
	#define VAL2 ("world")
	#else
	#define TYPE int
	#define PRINT(var1, var2)  printf("first = %d second = %d\n", var1, var2);
	#define VAL1 (-5)
	#define VAL2 (32)
	#endif

	- appDidInit:sender
	{
		Storage *store;
		TYPE a = VAL1;
		TYPE b = VAL2;
		TYPE *a1;
		TYPE *b1;
	
		store = [[Storage alloc] initCount:0 elementSize:sizeof(TYPE)
					description:@encode(TYPE)];
		[store addElement:(void *)&a];
		[store addElement:(void *)&b];
		PRINT(a, b);

		a1 = (TYPE *) [store elementAt:0];
		b1 = (TYPE *) [store elementAt:1];
		PRINT(*a1, *b1);
	
		return self;
	}

QA504	

Valid for 2.0, 3.0

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