david kaye dfkaye at yahoo.com
Fri Jun 28 17:07:11 PDT 2013


Eric -


On class-based inheritance

Gang of Four says prefer composition to inheritance, not avoid inheritance altogether.

As
 you suggest near the end of your last reply, you can use composition or
 injection with any of those constructors in the inheritance hierarchy 
to add or override behavior. It does not follow that we should never use
an inheritance hierarchy for generally shared or default behavior.

If
 the argument is against the class extends super syntax in ES6, I agree 
it's not necessary in ES.  But as others have pointed out, it's an opt-in 
feature that we won't be forced to use (big thank you to everyone for 
supporting backward compatibility).  As David Bruant noted, some prefer not to use Object.create() and just use new function() instead (I'm one of them - I'm guilty).

If the argument is against 
them in all cases, we still have to use care with mixins (see 
ActiveRecord for an extreme case) and interfaces, etc., as even a change
 to a trait or interface can have consequences downstream.


Out here in Userland

I've 
seen the same pathology you describe in several codebases - it also 
happens with CSS descendant rules and id selectors, !important rules and
 inline style attributes to override them *this one time*.  

But, I haven't seen coupling as a *problem* with inheritance per se so much as that a constructor is doing *any* work at all - by which I mean side-effects - which is an argument for using Object.create - which I now note with irony.  

The one thing that saved
 us from dread of *OMG we have to re-visit everything* has been reliance on unit tests - test-driven-development, or 
test-during-development really does reduce the fear of later confusion - but that's another discussion entirely.


Sorry for preaching to the choir and/or ruffling feathers


DFKaye





________________________________
 From: David Bruant <bruant.d at gmail.com>
To: Eric Elliott <eric at ericleads.com> 
Cc: es-discuss <es-discuss at mozilla.org> 
Sent: Friday, June 28, 2013 3:55 PM
Subject: Re:
 


Le 29/06/2013 00:14, Eric Elliott a écrit :

"I'm however very interested if you could take a look at the current proposal and tell if you can pin down how the current proposal makes classes harmful for code maintainability."
>
>Basically, my argument is that the whole paradigm of a class
          with a single ancestor, and any mention of that ancestor in
          the implementation of the child (referring to the parent in
          the constructor, for instance), is fundamentally flawed and
          problematic. `extends` harms code maintainability by virtue of
          creating the brittle hierarchy / gorilla-banana problem I've
          already described.
>
>The problem isn't how it's done in JavaScript or ES6. The
          problem is that it's done at all.
>
>Class gets people thinking in a fundamentally broken paradigm
          for good OO design
>
The rest of JavaScript remains. ES6 classes are just a sugar on top of the ES5 runtime concepts (objects with [[Prototype]], [[Get]], [[Set]], etc.).
People already think in a broken way when it comes to software.
    Software is hard. Lots of people model data inside strings. I
    believe this is a much bigger problem than classes. What's the
    solution for stringly typed code?


I saw a recent example of one of the problems with single-ancestor inheritance in a talk. I wish I could remember which one.
I believe it was this talk by Angus Croll https://speakerdeck.com/anguscroll/the-why-and-how-of-mixins-in-flight


The illustrations were great:
>
>Animal
>  - Walking 
>    - Monkey
>    - Human
>  - Flying
>    - Bird
>    - Bee
> 
>  - Swimming
>    - Fish
>    - Whale
>
>Now we need alligator and duck.
>
>I understand that JavaScript doesn't restrict you from doing things like mixins as well... but when you're 14 months into a project, and THEN you have to add the alligator, suddenly you're mixing paradigms in ways that diverge significantly from the style of the rest of the code base. At this point, the code is already arthritic and brittle. Fitting these things in at this point is a lot less trivial.
>
Classes and the single-ancestor pattern are limited in the sort of objects they can model. Animals are such an example.
But you can model other simpler things that don't have properties
    that cross over. Classes can work for these cases.
I believe that these cases are numerous and classes can work for
    them. 

Classical inheritance is a problem when that's the only tool you
    have. But if you have a decent understanding of what you're trying
    to model, you can use classes when that fits and other more
    appropriate mechanisms when they're available. The very tool you use
    to model something can already be of help to others to understand
    the "shape" of what you're modeling. 


If you're relying on things like super in the rest of the code, how does the new stuff properly invoke the constructors of multiple ancestors which are designed to be single ancestors?
>
Does the ES6 super has the same issue than the Java one? I really don't feel I have enough expertise in the matter to say yet. 


I can tell you how I've seen these situations handled in the real world, virtually everywhere the problem has cropped up (pretty much everywhere that class was relied on heavily). Massive refactors. Code rewrites. Lots of wasted time.
>
Yes, when the wrong tool is used for a job, people pay it later. It also happens in JavaScript. In my experience, it's often more a problem of not understanding your model enough when first writing the code. In my experience again, it's hard to plan everything in advance and choosing class or not class is rarely the heart of the problem when you've mis-modeled your software.


Class sugar might save developers a few keystrokes today, but it will come back to bite them hard later. Lots of people are paying for Backbone's .extend().
>
>If it added value, that would be one thing. But it doesn't
            actually do anything that couldn't have been done just by
            replacing it with a constructor that produced objects that
            could be passed into those constructors to produce new
            objects.
This sort of argument leads us nowhere. By that argument, we can remove maybe 70% of the JS built-ins. All the Math functions and constants can go, all Array.prototype algorithms... Object.create isn't even necessary if you have functions and 'new', etc.
Classes offer a nice sugar to cover *some* use cases, *some*
    modelisation cases. Among expert-enough people, using classes may
    become the sign of simple models (when there is no need for
    specialization) or simple specialization patterns. That's a good
    thing. It's not big, but it's a good thing.


I have seen the problems in code at Adobe, at Tout, and at BandPage (my last three jobs, that all used Backbone).
>
I would be interested in see code samples describing your problem. I do believe you and I agree with you by intuition, but I would love to have a fully-fleshed example to study it and fully understand it to understand if some code maintainability issues.


The problem isn't with Backbone's particular implementation. I had the same problems in C++, Java, and with John Resig's Simple Inheritance in JavaScript.
>
>The problem isn't with the ES6 implementation. It's the
            whole paradigm.
>
No, the problem is when people limit the way they think about software through this only one paradigm. If this paradigm is here alongside others, I don't see the problem. People have the choice. Some will make mistakes, but how different is it from today?

David

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