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Design patterns are! Posted on October 29, 2012

It all started Monday morning at college. Professor of Information Systems was talking about evolution of programming techniques and at the end of the chain was OOP. The pinnacle of program design. Well, no. Even professor admitted that OOP failed to deliver. (No word on FP though, I was kinda disappointing). This made me think about problems ofJava and the like. Some hours later I’m sitting in cafe Metropol above Kiberpipa having tea with some friends - freshmen from FRI. And one of them asks me if there is a class on design patterns. I give a puzzled look and say no and he goes on to explain he’s currently reading Design Patterns in C#. Apparently an awesome book that teaches you some general approaches to problems. But I have quite strong opinions on some topics. And one of them are design patterns. I believe they are and I said that. I didn’t read the GoF book and I don’t have any intention to do so in near future. But I’m familiar with some patterns. Mostly workarounds for shortcomings of OOP languages and contrived solutions to non-existent problems. And I explained this. Response was to paraphrase: “Well, MVC is a great design pattern”. But I argued that it isn’t a design pattern at all. Since everybody had a laptop, a quick wiki search cleared this up. It’s an architectural pattern. Not a design pattern. What are design patterns

So I asked him out of curiosity for some patterns from the book(also trying to prove my point). Singleton

Well I used this one, so I cannot say it’s bad. But I can still say it’s overused and when it lets you access mutable object graph. Because this leaks mutable shared data all across your code base. But it gets real messy with double locking and stuff like that. Luckily Java solves this with enum. Now design pattern becomes just a keyword. That doesn’t qualify as a pattern in my book. C# has static classes that are basically same thing, singleton instance held by the class loader. For some reason C# folks call this Monostate, but it’s the same concept. Concepts are important, because they’re language agnostic. Even though patterns try, they inherently aren’t. And just for the last nail in the coffin. Scala has object keyword that creates a singleton. Factory, static factory…

This one is also abused. You even have metafactories that produce factories. That’s exactly like currying but wrapped up in objects and contrived to the point you no longer see it’s currying. The only useful use-case for them is abstraction over constructors. That is, a single method that, depending on the arguments calls some constructor for the type it constructs. But again, this is hardly a pattern.

Decorator

Decorator in statically typed languages means just implementing an interface or mixing in a trait(scala). I don’t see the point here. That’s why interfaces(traits) exist. Proxy

My friend insisted that this is something like Strategy pattern(didn’t use the word) but from the other way. Proxy is the user of strategy object. Anyway strategy is just a wrapper for function value, nothing to see here. But not I googled it and I’m even more puzzled. It seems this means object reuse. Like literally sharing data. You know, like you do with any immutable values. Did I misread?

And about here we digressed to static vs dynamic typing. Sadly I was the only one for static. Apparently nobody wants compiler to help them. Now I’m sad. Compilers are one of the best programs out there. And with type inference they do all the work for you. You must be a fool not to use one and rather do a of unit tests instead.

So… and anyone point to a useful design pattern or am I right and they truly are?

links
https://en.wikipedia.org/wiki/Immutable_object

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

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