NSAssertionHandlerKey
A key with a corresponding value in the thread dictionary.
Declaration
let NSAssertionHandlerKey: StringDiscussion
If you need to customize the behavior of NSAssertionHandler, create a subclass, overriding handleFailureInMethod:object:file:lineNumber:description: and handleFailureInFunction:file:lineNumber:description:, and install your instance into the current thread’s attributes dictionary with this key.