It crashes only if you let it.

a) The crash is from the default unhandled exception handler, which will send a signal to abort. So if you just want to crash, you can either handle that particular exception or install a different unhandled exception handler

b) An object gets sent the -forwardInvocation: message when objc_msgSend() encounters a message the object does not understand. The exception above gets raised by the default implementation of -forwardInvocation: in NSObject.

    o := NSObject new.
    o class
    -> NSObject
    n := NSInvocation invocationWithTarget:o andSelector: #class
    n resultOfInvoking class 
    -> NSObject
    o forwardInvocation:n 
    2019-04-22 07:49:12.339 stsh[5994:785157] exception sending message: -[NSObject class]: unrecognized selector sent to instance 0x7ff853d023c0 offset: {

(This shows that -forwardInvocation: in NSObject will raise that exception, even if the NSInvocation is for a message the object understands)

If you override -forwardInvocation:, you can handle the message yourself. In fact, that is the last-ditch effort by the runtime. You will first be given the chance to provide another object to send the message to ( - (id)forwardingTargetForSelector:(SEL)aSelector; ) or to resolve the message in some other way, for example by installing the method ( + (BOOL)resolveInstanceMethod:(SEL)sel; )[0].

Cocoa's undo system is implemented this way[1], as is Higher Order Messaging[2][3]

[0] https://developer.apple.com/documentation/objectivec/nsobjec...

[1] https://developer.apple.com/documentation/foundation/nsundom...

[2] https://en.wikipedia.org/wiki/Higher_order_message

[3] https://github.com/mpw/HOM/blob/master/HOM.m

Back when I wrote a lot of obj-c is when I really 'got' message passing vs. a function call. I miss obj-c, but everyone wants to move on to Swift.

Wasn't the design decision (and implementation) involved in place log before Apple had anything to do with it?

NextStep adopted it but did not invent it. Once Apple acquired NextStep and released OS X they were the only major company supporting it and had defacto control over the language.

The complaint I have is with NSObject which can be blamed on Next Step. Although another comment pointed out I just didn’t know about a workaround.

There were two different major mutually-incompatible “flavors” of Objective-C (my first book on Objective-C covered both, and my first Objective-C programming was done on a NeXTcube), one of which originated at NeXT (NextStep was the OS that was NeXTs last major surviving product after they dropped hardware, not the company.)