Message Forwarding: Performance Trade-offs Between resolveInstanceMethod: and forwardInvocation:

The Objective-C runtime provides a multi-stage pipeline for handling missing selectors. When a message is sent to an object that does not respond to the selector, the runtime first attempts dynamic method resolution via resolveInstanceMethod:, followed by the forwardInvocation: mechanism.

While resolveInstanceMethod: allows for the runtime synthesis of a method implementation to prevent subsequent crashes, forwardInvocation: provides a more flexible redirection via NSInvocation. However, the creation of NSInvocation objects and the associated stack depth increase introduce overhead compared to direct method dispatch or dynamic resolution.

When designing a system that relies on these mechanisms for high-frequency calls, it is unclear where the performance tipping point occurs between these two strategies.

• What is the measurable performance delta between a method dynamically added via class_addMethod during resolution versus a call handled by forwardInvocation:?
• How does the overhead of NSInvocation object allocation impact execution time in tight loops compared to standard runtime dispatch?