Windows Bridge for iOS

DEV DESIGN SPECIFICATION: NSError + NSCFError

Feature Summary

NSError is a specially bridged class that, unlike other bridged classes, is subclassable without primitive method overrides.

Technology/Architecture Decisions

Because of its subclassable nature, NSError must implement all methods, and its alloc methods must return an NSError rather than an instance of the concrete bridged subclass NSCFError.

Design

NSError design:

• Unlike other bridged classes, NSError is not an abstract class and can be subclass without overriding any methods
• NSCFError is kept around as the bridged subclassed, but NSError alloc does not return NSCFError - only CFErrorCreate will return a NSCFError object
• NSCFError does not define any ivars and passes on all accessors to CFError
• NSCFError retain and release call CF equivalents, and CFRetain/Release recognize that NSError is not bridged while NSCFError is bridged
• NSError and NSCFError have identical memory layouts. CF accessors called on NSError therefore work appropriately. StrongId is used for NSError properties - while this does not strictly conform, we are safe because CFError accesses these properties only through getters.