Object Oriented Programming With Smalltalk - Objects and Messages 

I shall do. Be sure to follow the series using the playlist: ru-vid.com/group/PLZHx5heVfgEvuveKG1T7BBSuDOTHl1eLl

Thanks for the comments. More will be coming along in later videos. I'm trying to follow the Smalltalk/V tutorial very closely so that people can use that as the "course text" so the order of explanation is dictated by the order of the tutorial. It may be old but I still think it's a terrific tutorial. Very short, clear and methodical. I also like the fact that it lets me show how this old code can, with relatively few changes, be made to run in a modern Smalltalk. That said, my real focus is on trying to explain the core ideas of oop rather than just do another Smalltalk tutorial. Pharo and Squeak both have masses of tutorial material already. I'm hoping that my series might help people to bridge the gap between Smalltalk (which most viewers won't have used) and whichever modern oop language they are using. Best wishes Huw

Many thanks

Yes, there'll be more! I'm glad you find them of interest. Most of the code works equally well in Pharo though there will be a few differences re. graphics and Files. I may think of doing some Pharo lessons later on. I thought this series would be simpler to follow if I just used Squeak (and Smalltalk/V when I want to show a "historic" version). Bookmark the playlist if you'd like to follow the series in order. ru-vid.com/group/PLZHx5heVfgEvuveKG1T7BBSuDOTHl1eLl

in smalltalk in order to create a class or an object, you send a mesage, unlike these other languages.

also, control flow structures in smalltalk follow the same pattern, unlike in these other languages.

To be honest, It's a long time since I've read a Smalltalk book. I'm sure I've read at least some of "Discovering Smalltalk" in the past but it's not fresh enough in my mind to comment on it. I think this is one of the titles freely available online so give it a try.

@@LearnWithHuw thanks!

I talk quite a lot about that in several videos in this series. In short, the idea is that any object can receive any message but is up to the object to decide how (or if) to handle that message. You have to remember that when Smalltalk was released, most languages were *like C or Pascal) procedral with functions existing "free floating". One one function could have any given name. A function-call went straight to that function. OOP introduced "bound-in" methods where many objects could have functions with the same name. so messages were sent to objects. If anyone finds message-passing hard to understand, just think of methods as interfaces into objects.

@@LearnWithHuw, I think I understand message-passing. I'm just trying to understand how it's different from today's method-calling.

@@electrocatalyst I could be wrong, but after discussing it with chatGpt, lol, I came up with this response, which could be wrong: I think Smalltalk is a lot like Python. Thus, one difference is that messages are dynamic. They have late binding. When you send a message, the object searches for that method throughout its hierarchy until it finds it. It will check the method cache and method dictionary. If it doesn't find it, it responds with a message like "No such method". So, imagine Python. You take Python and create a method dictionary for all the methods in that class. You implement a message handler for the class that accepts messages, then map them to the dictionary. If it finds the method in the dictionary, it calls it with the implementation. Thus, instead of calling the method statically and passing the arguments, you go through this message handler to access the object and pass the messages. That's the difference as I know it. It's a more dynamic way. You could pass messages that can't be handled, and it will gracefully give you a "not found" message, like calling a method through a try block. It's like meta-class programming, if you ask me. Moreover, in Smalltalk, the documentation said that everything about an object is supposed to be protected, and the only way to interact with it is through these messages. So yeah, those are the differences as I understand them. I think there is a reason smalltalk failed, but Python is very successful. I think Python is basically a modern smalltalk equivalent with pragmatic approaches. Correct me if I am wrong, but there you go :) Additionally (just crossed my mind), it would be hard in C++ to do something like, send the object a message to do something dynamically, then have it respond if it has such a method. Statically, that would be problematic, since you have to dynamically do that. I'm sure you could implement such dynamic nature into your classes, but smalltalk seems to do it at a language level, which is pretty nice.

​@@electrocatalystI guess the difference is that, with method calling, the compiler will determine what method to call and emits code that invokes that specific method (early binding, done at compile time). With message passing, the decision which method to call is made at runtime (late binding, done at runtime). This means that you could have objects that change method implementations in between method calls, which I believe Smalltalk can do. It also makes it possible to send a message to an object that does not have a method to handle it: in Smalltalk you can create a 'doesNotUnderstand' method that takes as parameter a datastructure containing the message sent to it. It can then examine the message and decide what to do with it (notify the caller that the message is not correct, sending the message to another object that can handle it, etc.). This can also be useful in implementing the proxy design pattern: the proxy's 'doesNotUnderstand' method simply forwards the message to the proxied object instead of having to reimplement every method, all of which would have to call the corresponding method on the proxied object. This is what Alan Kay meant when he said 'extreme late binding of all things'. Note that there is of course a runtime cost associated with this, but that some Smalltalk implementations can optimize away some of it. I don't know any details about this aspect of Smalltalk, so if you want to know more about it, you will have to Google it.

@electrocatalyst In my understanding, "message sending" is a fundamental idea and "calling a method on an object" is just a concrete expression of that idea in code. You can watch the previous video in this series to understand more about "message sending" ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-lmAarC0Zhq4.html