It’s not just about practicality. Ruby is using message passing, not method calling. This is fundamentally different and a bit foreign to the larger community. Then ruby layers syntactic sugar on top that hides this.

Behind the scenes everything is a message passed using __send__ and you can do this directly as well, but you generally don’t.

So when you write

5.times { puts "Hello" }

It’s sort of expected by the average programmer that you are telling 5 to call the times method and expect it to exist and do what it’s told.

In reality you have indirectly sent a message that looks like

5.__send__(:times) { puts "Hello" }

What we are really doing is sending a message to 5 (the receiver) and giving it the opportunity to decide how to respond. This is where method_missing comes in to allow responding in a custom fashion regardless if a method was explicitly defined.

So you’re not telling 5 to call the method times, rather you are asking, “Hey 5, do you know how to handle the message times?”

These are fundamentally different things. This is actually super important and honestly hard to really grok _especially_ in ruby because of the syntactic sugar. I came from a C/C++ background originally, then Java and then moved to Ruby. After a few years I thought I understood this difference, but honestly it wasn’t until I spent a couple years using Objective-C where message passing is happening much more explicitly that I was able to truly understand the difference in a way that it became intuitive.

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anamexis 10 hours ago | parent [-]

I’m a rubyist, but how is message passing fundamentally different from method calling? I get that method_missing adds a twist, but your comment doesn’t explain what the fundamental difference is.

Especially in the context of Fixnum#times. How does message passing vs method calling matter there? #times is just a method on Fixnum.

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isr 8 hours ago | parent [-]

Because it leaves it up to the object being called what to actually do with the message. The object you're talking to might be forwarding its messages to another object in another ruby instance on another machine (if the current machine is getting fully loaded, etc), and the caller would be none the wiser. And crucially, the caller wouldn't have to be modified to enable this. The logic for this would be entirely within the object being called.

So the difference isn't just with method_missing.

With "method calling" as you put it, the program blows up if that object doesn't have that method, WHEN YOU CALL IT.

Basically, this smalltalk oo paradigm is about shifting where you put more of your logic. At & around the "call" site, or within the object whom you're calling & entrusting to do something useful with it.

All hearkening back to Alan Kay's original ideas about biology influencing how we organise code, and having a program be 1000's of "little black boxes" where work gets done by all these boxes talking to each other.

Which is why smalltalk (& ruby implements the Smalltalk object model to its entirety) actually has an awful lot in common with Erlang & other BEAM runtimes, even though those are functional languages. Because once you get beyond the techy buzzwords, the main ethos behind them is actually quite similar.

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anamexis 7 hours ago | parent [-]

I guess what I’m getting at, is that I don’t understand how the difference actually informs anything concretely, as in the example of Fixnum#times, where this discussion started. Why is it super important to understand this fundamental difference?

	▲	bigtunacan 7 hours ago \| parent [-]
		Fixnum#times isn’t a great example, I only used it since the parent used it to illustrate their confusion and quite frankly a concrete useful example is to complex for this format. ActiveRecord has changed a lot over the years, but as an example in the original ActiveRecord you used dynamic finders. None of the finder methods existed initially, but if you passed a message to an active record object for a non existent method rather than fail it would determine if that should be a method and then it would build and persist a method to the process for future calls. It allows for some really interesting and powerful applications in horizontally scaling as well.