4 ms·

This nil-swallowing behaviour works really well with the "out error parameter" pattern of Cocoa methods. In short, methods that can fail have a signature like:

This nil-swallowing behaviour works really well with the "out error parameter" pattern of Cocoa methods. In short, methods that can fail have a signature like: - (id)thingThatSometimesWorks:(NSError *)error; You can chain these to your heart's content. The one that fails sets the error and returns nil; following messages are sent to nil which does nothing and a particular characteristic of doing nothing is that it doesn't overwrite the error that was set. So you still get to see the error when the workflow finishes. As an objective-C programmer, I also have a tool in my toolbox which gives NSNull the same message-swallowing behaviour as nil. @implementation NSNull(GJLNilReceiver) - (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector { return [super methodSignatureForSelector:aSelector] ?: [NSMethodSignature signatureWithObjCTypes:"@@:"]; } - (void)forwardInvocation:(NSInvocation *)anInvocation { [anInvocation invokeWithTarget:nil]; } @end

KMag 4y ago
You're better off having an operator in your language that explicitly chains together methods returning Result<T,E>s. That way, you can easily get this behavior if that's what you want, but it's clear from reading the code that it's intentionally not quite a simple chain of method calls.
arcticbull 4y ago
I mean this with love, this extension to NSNull gives me a brain aneurism. If I had this in my codebase I wouldn't be able to trust anything in a collection.
- grahamlee 4y ago
  You might want to return NSNull instead of nil (easy to do: in fact I extracted this from an object in which the nil-return value is configurable but simplified it for the post), in which case it becomes map-safe because NSNull->NSNull on map. I use this pattern because then I can trust _everything_ in a collection. If an object, even an object that represents emptiness, receives a message, it will handle it and do something, even where that something represents emptiness.

KMag 4y ago

You're better off having an operator in your language that explicitly chains together methods returning Result<T,E>s. That way, you can easily get this behavior if that's what you want, but it's clear from reading the code that it's intentionally not quite a simple chain of method calls.

arcticbull 4y ago

I mean this with love, this extension to NSNull gives me a brain aneurism. If I had this in my codebase I wouldn't be able to trust anything in a collection.

grahamlee 4y ago
You might want to return NSNull instead of nil (easy to do: in fact I extracted this from an object in which the nil-return value is configurable but simplified it for the post), in which case it becomes map-safe because NSNull->NSNull on map. I use this pattern because then I can trust _everything_ in a collection. If an object, even an object that represents emptiness, receives a message, it will handle it and do something, even where that something represents emptiness.