NSNull

Singleton class that represents a null value in collections that don’t accept nil. Returns nil/NULL/0 for all unknown method calls.

Base Class

NSObject

Implemented Protocols

• MulleObjCSingleton
• MulleObjCValueProtocols

Methods

Singleton Access

• +null - Returns the singleton NSNull instance

Comparison

• -compare: - Compares with other objects:
  • Returns NSOrderedSame if other is nil or self
  • Returns NSOrderedAscending otherwise

Dynamic Method Handling

• -forward: - Returns NULL for all unknown method calls

Usage Example

// Get singleton instance
NSNull *null = [NSNull null];

// Use in collections that don't accept nil
NSArray *array = @[@"string", [NSNull null], @"another"];

// All unknown methods return nil/0/NULL
[null someRandomMethod];  // Returns NULL
[null count];            // Returns 0
[null length];           // Returns 0

Important Notes

1. Singleton Behavior
   • Only one instance exists per runtime
   • -init returns the singleton instance
   • Cannot be copied or retained normally
2. Implementation Details
   • Thread-safe singleton creation
   • Returns NULL/nil/0 for all unknown methods
   • Useful as nil placeholder in collections
3. Memory Management
   • Singleton instance is never deallocated
   • Retain/release/copy operations are no-ops
   • Safe to use across threads
4. Comparison Behavior
   • Equal to itself and nil
   • Less than all other objects
   • Consistent with Foundation behavior