Steve Jobs, NeXTSTEP, and early object-oriented programming (2016)

Side note... I feel similarly about the Java to Kotlin transition. Sooo much better. Although, I don't hate Java NEARLY as much as Obj-C.

Also, you're 100% right. The square brackets are what immediately repulsed me and continued to befuddle me even after years of experience with it. Also, everything just feels "backwards" to me if that makes any sense. Coming from Java/C#/JavaScript everything just seemed unintuitive to me at all times. Also, I think this was heavily compounded by using xCode which (at the time) was incredibly laggy. So, I'd mess up the Obj-C syntax and the IDE wouldn't tell me for what felt like forever. Often I'd make a change and hit "play" before the syntax highlighting caught up and that always felt infuriating.

I last used xCode about 4 years ago and it was still an issue then (even with swift).

Because it is. Obj-C comes from the Smalltalk lineage by way of Alan Kay, using message passing [0] versus method invocation. It's a subtle difference with huge implications to how you design systems. Method invocation won out mostly because of Java and C++, but there was a time it wasn't clear which was the better OO paradigm.

[0] https://en.m.wikipedia.org/wiki/Message_passing

"In contrast to the traditional technique of calling a program by name, message passing uses an object model to distinguish the general function from the specific implementations. The invoking program sends a message and relies on the object to select and execute the appropriate code."

Method invocation won out mostly because of Java and C++

but according to the wikipedia article java uses message passing.

supposedly the distinction is that i can have a generic method that gets called if a named method can not be found. in smalltalk that's doesNotUnderstand: in ruby it's method_missing. javascript used to have __noSuchMethod__, in php i can overload __call, in pike i do the same with defining a method called `(), and many more.

so are they all using message passing? and then if java is supposed to use message passing and javascript removed __noSuchMethod__ it seems that alone can't be the distinction.

if there is a distinction at all then it look more like an implementation detail that does not actually affect what kind of code you can write, and more importantly, based on that it is not at all clear that method invocation won out.

So, the gist of the difference is this: object-oriented programming is, at its core, about late binding. Specifically, delaying decisions about what code will run when until run-time. But there's still some wiggle room to decide how late certain decisions are made. Most mainstream object-oriented languages like Java and C# more-or-less wait until the start of run-time to decide, but at that point the mapping from argument type to which code is run is pretty much settled. (This isn't necessarily 100% true, but it's the general rule.)

In a system that uses message passing, it's pushed even later, to method invocation time. Basically, each object (actor, whatever) gets to decide what code will be executed to handle a message every time it receives a new message, even for messages of the same type. In practice, most the time it's always the same code. But the point is that this level of dynamicism is a first-class language feature and not just a thing you can accomplish with hacks.