[isaachier]

Here's an example of the distinct nature of Smalltalk's message passing:

Control structures

Control structures do not have special syntax in Smalltalk. They are instead implemented as messages sent to objects. For example, conditional execution is implemented by sending the message ifTrue: to a Boolean object, passing as an argument the block of code to be executed if and only if the Boolean receiver is true.

The following code demonstrates this:

result := a > b ifTrue:[ 'greater' ] ifFalse:[ 'less or equal' ]

https://en.wikipedia.org/wiki/Smalltalk

[hota_mazi]

But there's nothing specific about message passing to that example, you can do this with regular function calling:

For example in Kotlin:

    class Boolean {
      fun ifTrue(closure: -> ())
      fun ifFalse(... whatever)
    }
    
    a.ifTrue { /* do something */ }

[gambler]

Your class will not work without language-level if/else construct or something equivalent. In Samlltalk if/else is implemented purely through message passing. There is no "real" if/else.

IIRC, Smalltalk has Boolean class and two subclasses of Boolean: True and False. There is a single method with two arguments (:ifTrue:ifFlase). The method is then overloaded. True calls ifTrue argument. Flase calls ifFalse argument. This is happening dynamically, at runtime. Again, the mechanism is generic enough to fully replace all use cases of "traditional" if/else constructs.

Clearly, you haven't thought this through.

Edit: People here would do well to read this: https://pozorvlak.livejournal.com/94558.html

[WA]

Which leads to the well known callback hell, no?

[chriswarbo]

I think "callback hell" in this case would be caused by "boolean blindness" and/or lack of abstraction.

General-purpose programming languages, by their very nature, cannot provide us with constructs that are specially suited to our domain; they can only provide us with generally-useful building blocks, like booleans, integers, functions, etc.

We could try to solve our problems using only those languge-provided constructs directly, e.g. using maps-of-lists-of-booleans-of-whatever. In that case, we get "callback hell", pyramids/triangles of doom, etc. because the same code needs to implement our solution and encode information about our domain.

Alternatively, we can use those language-provided constructs to write our own domain-specific constructs; then use those domain-specific constructs to solve our problem.

I've worked with people who avoid this second approach because understanding the solution requires learning those domain-specific constructs, whereas in the first approach we already know how built-in constructs like booleans work.

The nice thing about Smalltalk in this example is that if/then/else, loops, etc. are not built-in; they're library code. This takes them off the pedestal that they occupy in other languages, and makes it easier to think about replacing them with our own tailor-made alternatives.

(Note that this isn't specific to message-passing style OOP; we can also do this with e.g. recursive functions for loops, induction schemes (e.g. Church encoding) for control flow, etc.)

[scroot]

In practice, Smalltalk methods tend to be very short. Having too many "callbacks" (really it's just asking Block objects for their value; the "lambdas" here are just objects too) is an issue of how you are designing things. A lot of if/else stuff is avoided simply by taking advantage of the kinds of polymorphism Smalltalk allows in the first place.