Comment by bunderbunder
1 year ago
This is another example of where you've got to read Wikipedia with a skeptical eye. That one in-passing mention of Java is incorrect. I don't know why it's in there, WikiBlame indicates that it's been there since 2004, which was the early days of Wikipedia when it was particularly unreliable.
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.
i understand your explanation, but i still don't see how i am supposed to tell the difference as a programmer. to be a first class language feature it has to be something the programmer can see and use consciously. the only feature there is the ability to have catchall methods, but while the existence of such a feature is an indication that very late binding happens, the absence of it does not indicate otherwise. so it goes back to pretty much all dynamic languages with a runtime probably use message passing because they either do have such a feature or could have it. but i don't see that claim supported anywhere. everyone just seems to talk about how smalltalk is somehow different, but i can't see how it is different from javascript, php, pike or other dynamic languages.
and i believe what you say about java and wikipedia. it just shows again that the distinction is not obvious.
i found this discussion on stackexchange: https://softwareengineering.stackexchange.com/questions/3352...
but reading that doesn't help me to tell the distinction between java and smalltalk either. the point appears to be that all OO is message passing, and the only distinction as far as i can tell is that java doesn't have extreme late-binding of all things, but that is something i can't know just by looking at the language. it's a hidden implementation detail. not being able to tell how the message is processed is another feature that message passing is supposed to have, btw.
the stackexchange answer however also shows why i am not seeing any revelation when using smalltalk. if all OO is supposed to be message passing then it's no wonder, it all looks the same to me.
note that i don't want to argue either way. i don't know enough about this to make any kind of argument. and i am trying to figure out the right questions to ask so i can learn and understand more. your comment did help me move forward at least. thanks.