MulleObjCTaggedPointer

Protocol for implementing tagged pointer support in mulle-objc. Tagged pointers store small values directly in pointer bits to avoid heap allocation.

Required Methods

Value Access

• +mulleTaggedPointerClass - Get class for tagged pointer
• +mulleTaggedPointerFromIndex: - Create pointer from index
• -mulleTaggedPointerIndex - Get index from pointer

Validation

• +mulleIsTaggedPointerClass - Check if class supports tagging
• -mulleIsTaggedPointer - Check if instance is tagged pointer

Helper Functions

• MulleObjCTaggedPointerCreate - Create tagged pointer
• MulleObjCTaggedPointerGetClass - Get pointer class
• MulleObjCTaggedPointerGetIndex - Get pointer index

Usage Example

@interface MyNumber : NSObject <MulleObjCTaggedPointer>
@end

@implementation MyNumber

+ (BOOL) mulleIsTaggedPointerClass
{
    return YES;
}

+ (instancetype) mulleTaggedPointerFromIndex:(NSUInteger)index
{
    return MulleObjCTaggedPointerCreate(self, index);
}

- (NSUInteger) mulleTaggedPointerIndex
{
    return MulleObjCTaggedPointerGetIndex(self);
}

@end

// Usage
id number = [MyNumber mulleTaggedPointerFromIndex:42];
NSUInteger value = [number mulleTaggedPointerIndex];

Important Notes

1. Memory Layout
   • Bit patterns
   • Alignment rules
   • Platform specifics
   • Value ranges
2. Thread Safety
   • Thread-safe creation
   • Safe access
   • Handle concurrent use
   • Consider TAO rules
3. Best Practices
   • Check validity
   • Handle errors
   • Document usage
   • Test thoroughly
4. Performance
   • Avoid allocation
   • Fast access
   • Consider inlining
   • Handle contention

Note: Tagged pointers are an optimization that avoids heap allocation for small values by storing them directly in pointer bits. This improves performance and reduces memory usage.