Why Ruby Class Methods Resist Refactoring
blog.codeclimate.com
blog.codeclimate.com
The original was the easiest to understand, and the refactored versions didn't expose much that would benefit from testing or code reuse. This feels over-engineered to me.
And not to nitpick, but since when is class << self an ugly form? It makes perfect sense if all methods will be class methods.
Btw, I think its a small nitpick. Plenty of great code bases use "class << self".
My rule of thumb is to use class methods as factories to initialize your object in a certain way, which is quit consistent with what the class method `new` does. Once you stay in that line of thought the rest flows quit naturally without over-thinking anything.
A class method in ruby is not a static method. It is an instance method on the class. It sounds like nitpicking, but the distinction is real. You call #new on a class because the class is The Thing that makes objects, not an awkward pseudo-global scope. Class methods should thus be things for which the class is the subject.
Why not write a function? This addresses all of the objections. Then refactor by pulling out concerns into other functions.
Need to share logic around the functions? Use a decorator. Passing too many attributes? Create a class to contain them.
I think classes are best avoided until it's obvious that encapsulating state provides a benefit, which I don't see in this case.
Functionally though, there isn't much difference between Module.do_stuff() and module_do_stuff() and if you are writing functional code, there isn't much reason to care either way too much. Most Ruby I see though isn't terribly functional.
You can store a proc in a variable or a constant, but you're getting into some very ugly patterns at that point and you still haven't really left classes behind.
In Ruby everything is encapsulated and there's really no point in fighting that.
So exactly the same as Python then?
> You can store a proc in a variable or a constant, but you're getting into some very ugly patterns at that point and you still haven't really left classes behind.
How so? If you need to pass around something that quacks like a proc, do it as a proc.
Recently? Sort of, yes. Though in python it's more like everything has a blessed hash, and the assumption that everything is an object is much more thoroughly baked in in Ruby. Also the way that classes interact with their instances is quite different.
For example, in python a member of the class that is not overridden in an instance also happens to be a member of an instance. This is how default attributes work:
>>> class x(object):
... pass
...
>>> x.blah = 1
>>> x().blah
1
This kind of blending of instance and class doesn't happen in Ruby. The class is a completely distinct object with its own independent state, and is instantiated just like any other object, some syntactic sugar aside. It is an instance of class Class and its methods are the methods of class Class, while instances created by calling its #alloc method have the methods that are defined on it.
Python now shares some concept of everything being an object, I'll grant, but their models remain quite different and you really do have to work significantly against the grain to effectively use ruby in a non-OO fashion. In ways you simply don't in Python.
For example, you can have a Model.foo method that seems harmless enough, except that actually calls other methods on other models to do some calculation that maybe two or three layers deep makes a call to an external service. Let's say for the sake of example that two or three levels of database queries and api service calls ends up spawning hundreds of queries and at least dozens of external api calls. This takes anywhere from 10 to 30 seconds if the dataset is large enough.
A junior programmer would think he is doing the right thing by simply calling Model.foo because he might be so foolish to not know the difference between Model.foo and Model.foo(). Since Rails by default doesn't annotate database model attributes, it's even easier to think that Model.foo Model.bar Model.whatever are just attributes so there would be no performance penalty for using them.
As it turns out, this makes your code terribly slow even though it looks "elegant" and "clean". Why? Because it is super non-obvious to many/most programmers that there is a potentially huge difference between a simple attribute on a model vs. a calculated attribute method derived from potentially a multitude of other data sources. When you are calling Model.foo and Model.bar, it is completely unclear that one might be a method and one might be an attribute.
I've seen this happen many times to both really good and really average Ruby programmers. At this point it is a genuine flaw in Ruby that is compounded by the way I see people using ActiveRecord and Rails.
If you're calling Model.foo or Model.bar, you don't care about the specific implementation, you just want foo or bar.
The calling code doesn't need to know how Model works.
This way you can refactor either ones into normal attributes down the road without changing any dependant code.
If I care to call person.eye_color, I don't care (as the caller) how Person implements eye_color (it may be a simple attribute or do some ridiculously slow color calculation) - if I need the color, I need the color. Now, that's not to say that performance doesn't matter, just that any performance concerns should be addressed in Person, not in trying discourage caller from calling eye_color and trying to get at that value some other way.
That same logic would suggest that we should name our methods Model.foo_slow() and Model.bar_fast() because the execution speed is important and should be transparent to the caller.
In practice, Model.foo() ends up often being memoized so that all but the first call are practically equivalent to accessing an attribute.
Your suggestion violates the uniform access principle: http://en.wikipedia.org/wiki/Uniform_access_principle
In my experience ActiveRecord doesn't handle that particularly well and programmers don't readily know/see the difference because they all look the same, especially in a view.
Also, as far as Ruby is concerned your class's external API is only made up of methods. There are no attributes, model.foo is always a method. Because of this your long running or resource intensive methods need to be documented or have clear names if you are exposing them as public API. In other words: Model.foo shouldn't take 30seconds, but maybe Model.download_foo will.
Actually the problem he is describing is a consequence of language design, not of architecture design.
In Javascript, if I write foo.bar, I know that it is accessing some field of the foo object, and that's it. Unfortunately we're going to get a bunch of stuff in ES6 that's going to change this, but the fact that we can have some invariants (especially in a dynamic language like Ruby) on property accessors is pretty important when trying to reason about performance.
The fact that Ruby only exposes methods is a language design decision that can enable some pretty bad architectural decisions.
Language features are about tradeoffs .For example, among other things, the calling syntax for ruby means that point-free functional programming is pretty much impossible (though there are possible language-level solutions for this). Depending on what you're looking for, that can be considered a flaw , because it deviates from your personal definition of the ideal programming environment.
For CoffeeKit specifically, the getters for all accessor
properties are totally without side effects. They are getters
because they have to wrap access through objective-c selectors.
I can't make them fields. I also can't in good conscience
make them all functions, requiring people to write:
uikit.UIScreen.getMainScreen().getBounds()
instead of:
uikit.UIScreen.mainScreen.bounds
yuck.
Ruby on Rails definitely leans towards reducing verbosity, but it has such a good ecosystem that even though I'd like a platform that makes things a bit more apparent about what things have/don't have side effects, it's still the best option for many projects that need to be created fast and maintained into the future. I'm looking forward to ES6 generators in Node.js, since they promise to create an ecosystem that avoids "callback hell" but still make it explicit where, in each level of code, expensive operations might occur [2].
[1] https://blog.toshokelectric.com/why-im-ditching-coffeescript... [2] http://zef.me/6096/callback-free-harmonious-node-js
The syntactical equality between a variable and a method call on self has the advantage to make things like this possible. E.g. if i have:
foo = DataBase.lazy_load(:foo)
do_something_with(foo)
def foo
DataBase.lazy_load(:foo)
end
do_something_with(foo)
Also, you are complaining about the Rails API more than anything else. E.g. in DataMapper, it was quite obvious that those attributes do hard work (e.g. coercion), because you had to explicitly define them in the first place.
f :: () -> T is a function that still takes a (meaningless) value
g = map f list is just a value.
The only even superficial ambiguity is between calls to methods on the current object and local variable references.
> For example, you can have a Model.foo method that seems harmless enough, except that actually calls other methods on other models to do some calculation that maybe two or three layers deep makes a call to an external service.
That's not a lack of clear difference in code between a method and a variable, since when its referenced in external code its unmistakably a method, not a variable reference (its quite awkward to reference an object's variables from outside in Ruby). Its that Ruby is doesn't have syntactic conventions which imply things about the implementation of methods (the way, e.g., C# has with properties, which are simply a gate way to call methods, though there are fairly strong -- though not universally observed, and therefore dangerous to rely on -- conventions about what the underlying getter and setter methods should and should not do.)
Personally, I think Ruby's way is the right way if you don't have strong and language (e.g., compiler) enforced guarantees.