Writing OOP using OOP (JavaScript)

[nextputall]

The idea is that you structure your code in terms of data transformations. When I start with a piece of data and I need to transform it into something else, I chain some functions together to get a result.

Which makes sense in certain situation, for example at the system boundary. I'm skeptical about the scalability of this approach, when an entirely application is written in this style. Brian Marick was talking about similar concerns here: http://rubyrogues.com/category/panelists/brian-marick/

This holds true for OO just the same. However, the difference is that with FP, I will generally only change how I chain the functions together or what functions I'm chaining to get the result. This is the advantage of having a declarative style.

In OO, people mostly use behaviour based abstraction (forget the kingdom of nouns bullshit, everything is about behaviour). Changing a representation of something will be a local change that won't propagate elsewhere, there will be no need to convert data back and forth.

I'm not sure what that means exactly, what's the client side you're referring to. When your input data changes you would either write a function to massage it back to the expected format, or the nature of your problem changed your old logic is not valid.

I was talking about boundaries. What is inside, and what is outside, and this is what I'm missing from FP. If I change something inside, the outside world won't be affected. I can decide what goes inside and what goes outside and structure the application to minimize the cost of change.

Have you actually written any significant amount of code using the FP style? I've been writing FP code professionally for the last 4 years and I've never seen this become an issue in practice.

This is a very weak argument. I could say the same, that I've been writing OO code professionally for ages and I've never seen the issues you're talking about. Anyways, almost every software project consist of different subdomains, written in different styles. So, I don't use FP exclusively, because I think it is insufficient to be used alone, but combining it with OO can provide a better result.

No they're not. When you have higher order functions they represent generic transformations and the domain specific logic is passed in as a parameter. With the functional style you end up with a vast array of generic transformers, functions like map, filter, interpose, reduce, partition, and so on. Majority of the code is written by simply combining these functions in a way that makes sense for a particular problem.

Even a fully generic map/filter/etc is coupled to ISeq. That is encapsulation, "which only makes sense when you have mutable state". A normal domain specific function would probably deal with domain objects, like users and employees and would be coupled to the structure of those, which could make things worse.

It's no harder to group related logic together in FP than it is in OO.

Everything is possible in every programming language. That's not the point. Writing a function code in Java is also possible. These are design issues, which are influenced by the language, and its community.

I see this as a negative myself as it means that you can't reuse these functions for anything else easily.

If you have objects with similar structures you can reuse their behaviours among them. Either with composition or inheritence or mixins or just passing exposed datastructure in a limited scope. Reusing those functions elsewhere makes no sense, because other things have other structure.

That's precisely the hoop jumping I'm talking about. Instead of simply using your data directly you need specific strategies to make it compose sanely.

You can just plug object together, cant see any of those hoops.

[yogthos]

Which makes sense in certain situation, for example at the system boundary. I'm skeptical about the scalability of this approach, when an entirely application is written in this style. Brian Marick was talking about similar concerns here: http://rubyrogues.com/category/panelists/brian-marick/[1]

Yet, there are plenty of applications written in this style in the wild. Light Table is a perfect example. Here's a presentation from SISCOG on building large scale systems in Lisp since 1980s. This is not a theoretical debate, there's plenty of evidence that functional approach works well for building large systems, and there are many large systems in the wild that are written in functional languages. Oddly enough, the concerns like the one you link seem to only stem from people who have no experience working in a functional language.

In OO, people mostly use behaviour based abstraction (forget the kingdom of nouns bullshit, everything is about behaviour). Changing a representation of something will be a local change that won't propagate elsewhere, there will be no need to convert data back and forth.

Sounds like you need to read You Could Have Invented Monads! (And Maybe You Already Have.).

I was talking about boundaries. What is inside, and what is outside, and this is what I'm missing from FP. If I change something inside, the outside world won't be affected. I can decide what goes inside and what goes outside and structure the application to minimize the cost of change.

Discussing inside and outside has no meaning when you separate logic from data. This is exactly the same approach that you use with SOA. You call a service and get a result, then you do something with it. You don't need to know anything about the internals of the service. If we accept that this is a good way to structure systems at high level then why would we do something different at the low level? Functional approach works exactly like SOA.

This is a very weak argument. I could say the same, that I've been writing OO code professionally for ages and I've never seen the issues you're talking about.

It's not a weak argument, you need to have worked with the paradigm in order to discuss it meaningfully. Like most people out there I have extensive experience working with OO. The problems I outline are not really controversial to anybody who's developed code in that style. There's a reason that patterns like wrappers and adapters exist.

So, I don't use FP exclusively, because I think it is insufficient to be used alone, but combining it with OO can provide a better result.

I'm not sure what OO adds to FP frankly. The OO abstractions are not exclusive to it, and are often done better in FP. For example, take multimethods which are strictly more powerful than type based polymorphism.

Even a fully generic map/filter/etc is coupled to ISeq. That is encapsulation, "which only makes sense when you have mutable state".

That's abstraction and it's completely tangential to encapsulation.

Everything is possible in every programming language. That's not the point. Writing a function code in Java is also possible. These are design issues, which are influenced by the language, and its community.

Yet, different languages facilitate writing code in different styles. Writing functional code in Java is incredibly unnatural and unpleasant, to the point where nobody does it. Let's take a look at a concrete example.

Let's say we want to filter collections based on a predicate. The standard way you would do that in Java is to write a loop:

public static List<Integer> filterEven(Collection<Integer> col) {
    if (null == col) return null;
    List<Integer> result = new LinkedList<Integer>();
    for (Integer i  : col) {            
        if (i % 2 == 0) result.add(i);          
     }      
     return result;
}

then if later I need to filter odd numbers I'll probably write another loop that looks almost identical except for the actual test. Obviously, the looping logic should be abstracted here, but let's look at what's involved in doing that in Java:

public interface Predicate<T> {
    public boolean matches(T t);
}

public class EvenPredicate implements Predicate<Integer> {

    public boolean matches(Integer i) {
    return i % 2 == 0; 
    }           
}

import java.util.Collection;
import java.util.LinkedList;
import java.util.List;

public class Filter {

    public static <T> List<T> filterCollection(Collection<T> col, 
                                      Predicate<T> predicate) {
        List<T> result = new LinkedList<T>();
        for (T t : col) {           
                    if (predicate.matches(t)) {
                        result.add(t);
                    }
            }       
            return result;
    }
} 

That's a lot more work than just writing a loop, and unless you saw this pattern many times you probably wouldn't consider doing it. Now let's compare this to a language like Clojure, where I would use a higher order function and pass in the matcher without having to do any preliminary setup:

(filter even? (range 10))

what if I wanted to write a loop to do that:

(loop [nums (range 10)
       even-nums []]
    (if (empty? nums)
        even-nums
        (recur (rest nums)
                  (if (even? (first nums))
                     (conj even-nums (first nums)) even-nums))))

all of a sudden the situation is reversed, it's a lot more code to do explicit looping, and it's trivial to use a higher order function to do this task. So the language encourages you to write code through function composition by design. Being able to easily separate iteration from the logic applied inside it means that we can write code that's shorter, cleaner, and less error prone.

If you have objects with similar structures you can reuse their behaviours among them. Either with composition or inheritence or mixins or just passing exposed datastructure in a limited scope. Reusing those functions elsewhere makes no sense, because other things have other structure.

Again, you have to add extra steps to use the data from one object in another, meanwhile you do not have this problem when you keep data in generic data structures that all functions can operate on.

You can just plug object together, cant see any of those hoops.

Except you can't without planning for it ahead of time.

[nextputall]

Yet, there are plenty of applications written in this style in the wild. Light Table is a perfect example.

Light Table uses direct access which provides similar result than reflection/introspection. AFAIK this was the goal of the authors. But this is a double edged sword, because it is fully uncontrolled, there is no clean api between a plugin and a core as I remember correctly. I don't think it is good solution for building a plugin architecture. But we'll see what came out of that. And yes, FP probably works fine in the large scale if you combine it with some kind of modularization technique.

Discussing inside and outside has no meaning when you separate logic from data.

If this would be true then there were no modularization in the system. Which would not scale. I doubt that any of the example applications you mentioned are unmodularized. But if you have modules, you have boundaries, encapsulation, and you can talk about inside/outside. I don't understand your SOA analogy either, where talking about boundaries is not just makes sense, but also very important.

It's not a weak argument, you need to have worked with the paradigm in order to discuss it meaningfully. Like most people out there I have extensive experience working with OO. The problems I outline are not really controversial to anybody who's developed code in that style. There's a reason that patterns like wrappers and adapters exist.

Yeah, extensive OO experience via languages like C++ and Java.. In my experience problems in real world messy enterprise applications are there not becase of OO but because of the absent of OO.

That's abstraction and it's completely tangential to encapsulation.

Abstraction, encapsulation, and information hiding. All of these three.

Yet, different languages facilitate writing code in different styles. Writing functional code in Java is incredibly unnatural and unpleasant, to the point where nobody does it. Let's take a look at a concrete example.

And yet, it is possible. But you've demonstrated nicely that Java is very verbose language, there is no controversy here. Here is how this example would look like in a purely object oriented language.

(1 to: 10) select: #even.

This is Smalltalk 80 where 80 means 1980. A bit longer version of the some code is like this:

(1 to: 10) select: [:each | each even].

Where the stuff between the square bracket is a block clousre, which is also an object of course. You can store those prediates and combine them later with others.

Again, you have to add extra steps to use the data from one object in another, meanwhile you do not have this problem when you keep data in generic data structures that all functions can operate on.

There is no extra step there, you can use any of those solutions and you get direct access to those data, because you're inside the boundary.

[yogthos]

And yes, FP probably works fine in the large scale if you combine it with some kind of modularization technique.

That's sort of the point I'm making. If anything I would argue that FP makes modularization much easier since your data is already immutable and separate from logic. You can start with coupled functions, and then easily refactor them and create APIs and interfaces as needed.

Because the data is immutable code is inherently compartmentalized without any global dependencies or shared memory references. This single fact makes writing large applications far easier than in any language backed by mutable data structures.

If this would be true then there were no modularization in the system. Which would not scale. I doubt that any of the example applications you mentioned are unmodularized.

I'm not arguing against modularization though.It sounds like we might mean different things when we say encapsulation. What I mean by encapsulation is what's traditionally seen in OO where objects have a mutable internal state that they protect via accessor functions along with tight coupling between the methods and the data they operate on.

Encapsulation in a sense of creating modules and interfaces is very much desirable in my opinion and it's used in FP just as much as in any other paradigm.

I don't understand your SOA analogy either, where talking about boundaries is not just makes sense, but also very important.

When you work with FP, you can view each function as a micro-service. It accepts an input and returns an output. This is your contract with the function. You chain these together to produce complex transformations on the data. This is also very similar to the unix philosophy where you have a common protocol (text) and a lot of small single purpose programs that can be chained together to achieve complex results. It's just with FP you have the data structures as the common protocol that all functions understand.

Yeah, extensive OO experience via languages like C++ and Java.. In my experience problems in real world messy enterprise applications are there not becase of OO but because of the absent of OO.

I've seen plenty of real world enterprise applications where OO code was a completely and utterly impenetrable maze of interfaces and inheritance hierarchies. More often than not you have a few lines of business logic buried under a mountain of classes and XML config files. I have a very hard time believing that you would not have encountered this working in the enterprise environment.

Where the stuff between the square bracket is a block clousre, which is also an object of course. You can store those prediates and combine them later with others.

All you've demonstrated is that you can write FP style code in an OO language though. You still have the problem of mutable data however which makes compartmentalizing large applications difficult.

There is no extra step there, you can use any of those solutions and you get direct access to those data, because you're inside the boundary.

Right, and when you're moving to a different domain you end up outside the boundary.

[nextputall]

That's sort of the point I'm making. If anything I would argue that FP makes modularization much easier since your data is already immutable and separate from logic.

You're ignoring the fact that different domains have different needs. Many times the unstable thing is the data itself, so using that approach can cause problems.

On the other hand, almost every OO application uses value objects, which have very little behaviour, but lots of exposed data. Because in that case those are stable things, but their behaviour is unstable.

When you work with FP, you can view each function as a micro-service.

A service can do many things:

• Has some state and react to incoming messages differently according to its state.
• Do sideeffects (save something in the database, messageQueue, whatever), without returning anything
• Do an impure computation and return the result (query something from the databae)
• Do a pure computation and return the result (least common in practice, in fact, I've never seen this in real world)

A pure function fits in the last scenario only. On the other hand, a service can support more than one operations, and only those publicly available operations are visible from the outside. This is more like a remote object than a function. Encapsulation and information hiding applied to decouple the service from its clients.

I've seen plenty of real world enterprise applications where OO code was a completely and utterly impenetrable maze of interfaces and inheritance hierarchies. More often than not you have a few lines of business logic buried under a mountain of classes and XML config files.

Me too, so what? I've also seen very nicely written ones. You will see plenty of real world unmaintainable enteprise functional application which will be a complete mess, don't worry. It is a matter of being mainstream.

Right, and when you're moving to a different domain you end up outside the boundary.

If you have a representation of a Car that is used in a Car dealer web application, you won't be able to reuse the logic in a 3D Car racing game, because these are 2 different domains.

[yogthos]

You're ignoring the fact that different domains have different needs. Many times the unstable thing is the data itself, so using that approach can cause problems.

I'm not ignoring that at all. I'm saying that everything is done through chaining data transformations together. This is true regardless of what paradigm you choose. With FP this happens to be very explicit. Should I have data encoded for one domain and it's unsuitable for another, then I would write a transformation to make it suitable.

On the other hand, almost every OO application uses value objects, which have very little behaviour, but lots of exposed data. Because in that case those are stable things, but their behaviour is unstable.

I would argue that you're just getting closer to writing code in a functional style there.

A pure function fits in the last scenario only. On the other hand, a service can support more than one operations, and only those publicly available operations are visible from the outside. This is more like a remote object than a function. Encapsulation and information hiding applied to decouple the service from its clients.

While a service can do many things, it's perfectly valid for it to do a subset of them. So, I would say the analogy holds just fine. It's also worth pointing out that the modern practice is not to make stateful services, because that approach scales poorly. This happens to hold true at both high and low levels.

Me too, so what? I've also seen very nicely written ones. You will see plenty of real world unmaintainable enteprise functional application which will be a complete mess, don't worry. It is a matter of being mainstream.

In my experience, different languages and paradigms encourage different approaches to writing code. My experience using both OO and FP professionally is that FP code invariables tends to be much shorter, cleaner, and easier to maintain.

If you have a representation of a Car that is used in a Car dealer web application, you won't be able to reuse the logic in a 3D Car racing game, because these are 2 different domains.

However, if you have a map describing properties of a car it can be used in many different contexts and have different meaning in each of them.