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The Developer's Dungeon
Yesterday I was browsing one of the online...
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You have done a good job with the explanation. I think the bigger picture is that the SOLID principles are a specific application of computer science principles to OO. For example, Separation of Concerns and polymorphism are not specific to OO. And SOLID simply directs some of those more general concepts at OO.
I do not think the SOLID principles apply to FP, but instead the more general CS concepts apply. I am being slightly disagreeable here for a practical reason. When I was a new functional programmer, I tried to apply OO principles to learning FP. And it made learning FP difficult. In fact I gave up the first attempt. I find that the best way to approach learning FP is to treat it as structured programming with a few new rules such as: immutability, deterministic functions, and using expressions instead of statements.
For a more humorous take on this topic, check out this great presentation by Scott Wlaschin.
Which has this hilarious slide that saw some circulation.
Hey Kasey, thanks for writing this. I heard that about learning functional programming many times, unfortunately for me I still haven't found a way of letting go of everything related to oop, probably with time the functional side will get better. Right now I am in that case you describe. I already watched that talk from Scott is super good though I haven't got into F# yet.
From my experience, really the only way in is learning-by-doing, and best using a language that simply doesn't allow you (or makes it uncomfortable for you) to fall back into OOP thinking. For me that language was Clojure, for some it is Haskell or F#. I never used or looked at F#, but I heard good about it, too. I think learning one of these three and applying them in a real-world scenario will just ease you into FP as a "byproduct".
Thanks for the comments, I agree with everything you said. I also like the approach of learning with a language that doesn't let you fall back. I am also learning with Clojure. I tried Haskell but it was too much for me. So far Clojure has been a very pleasant experience but I still have a long way to go. I am still with the basics. I am using a book called "Functional programming for the object oriented programmer" by Brian Marick, is quite good
Thanks for the comment. You can retain all your OO knowedge while learning FP, but maybe just put it in a box to the side. :) It is helpful to look at it as going back to basics. You just have data structures and functions, maybe like Go. That is a good starting place for the journey. I wrote an introductory article here. It is for F#, but the principles should apply to OCaml, Haskell, or Reason.
put very diplomatically!
What a fabulous article, thanks for sharing! I have recently been trying to bridge the gap of OOP Design Patterns and functional programming myself, so I'm interested to read your next article. Maybe I can give some food for thought based on what I've been thinking about!
I program web backends in Java at my day-job but prefer the immutable & functional language Elixir for personal projects. They are vastly different languages but I find surprising parallels in how they're used. The primary Java backend I contribute to leverages the Visitor pattern to extend the behavior of objects that hold data, without having to define the behavior in their class definition. It seems like a good approach because it's made the service extensible in a variety of ways.
The more I worked within the bounds of the Visitor pattern, something became more apparent: it seems that the Visitor Pattern is actually just achieving one of the core principles of functional programming, which is to decouple structured data from its behavior! Another couple of OOP Design Patterns that I think achieve functional principles:
I therefore think that some OOP Design Patterns, when applied, are actually making programs written in OOP languages more functional... I think it's really hard to think of OOP and FP as black and white; you can write FP code in an OOP language, and you can also write OOP code in an FP language. It's not worth arguing about which paradigm a program is written in or isn't, it's about which paradigm the program is more of. I'd like to hear your thoughts on this :)
Hey Christian how are you? Thank you very much for that answer. It really have me something to think about. I never thought about the case of the visitor pattern, I am gonna have to check it better before my next article. I did saw the similarities you mentioned on the strategy pattern and the observer pattern, though in functional programming the benefits of the strategy pattern are much easier to achieve due to first class functions. I also see some similarities between function composition and the composite pattern. I definitely believe that a lot of the design patterns were created to give oop languages the flexibility that functional languages get for free without losing the control over data and state (at least in theory ahaha)
Doing great, you've had me thinking about OOP design patterns over the last few days. I think we're saying the same thing wrt the strategy pattern; it's a means of taking some functions and composing their inputs & outputs through a centralized code module, which is what all programs written in an FP language look like. What similarities do you see between Function Composition and Composite Pattern? I see the Composite Pattern more as a means of representing a tree structure in a strongly-typed OOP language, is this what you mean when you say Composite Pattern?
Ooh, I really appreciate your observation "a lot of the design patterns were created to give oop languages the flexibility that functional languages get for free without losing the control over data and state." I've been trying to put that into words for awhile now
A very good explanation! I never really consciously thought about SOLID. I do also think that the principles it describes do apply to Functional Programming, but in a very natural way. I'd go so far as to say that SOLID is a guideline of applying a few principles from the functional world in the object oriented world.
I consider it amazing that you get that much attention with this topic. You clearly hit the bull's eye! I will add a corresponding OO-related chapter to my FP online course.
I am glad I was of help ahah. Could you please post your online course when it is done? I would be interested in checking it 😀
Of course: A fool's scriptum on functional programming
Nice explanation.
TBH, it was pretty hard to put all these theories together, but you made it easy to understand. Thanks.
Thanks for reading it, I am glad you liked it. Yeah, it is more of my own analysis on how these principles apply so It can be hard to put into words.
I am glad you liked it. The idea has been in my mind for a while now so I will probably write an article about it next week or so 😀
I am glad it helped, now I don't remember if they are explained in Clean Code or if I originally read about them somewhere else. I am gonna check and report back.