Re: [Haskell-cafe] How to fulfill the "code-reuse" destiny of OOP?

Somehow, I agree with you. I think inherit is not evil, the people use it wrong is. The problem here is, inherit is naked right now. So people could use it wrong. On Fri, Oct 30, 2009 at 7:42 PM, Yaakov Nemoy wrote:

2009/10/30 Peter Verswyvelen :

...

The following is purely my own experience, I have no links to papers of clever people :)

I think none of the inheritance techniques work perfectly. E.g. describing everything with OO interfaces (=a extensible record of function pointers) is also problematic IMHO, at least when you have side effects.

The problem with an interface (with side effects) is that people using the interface tend to depend on the side effects that a particular implementation of that interface performs. So in order to describe the "contract" for implementers of an interface, one often has to go into great detail.

Also in Haskell it is required that an implementers follows the "contract" when implementing a type class, e.g. when writing a monad, you must make sure it follows the monad laws. But  at least in Haskell, this can be proven, while in OO, one has to hope that the side effects of an implementation won't cause weird behavior elsewhere. In practice, this seems to work, most of the time :)

The evolution of industrial OO the way I see it, is strange. You start with assembler, in which it is obvious to extend records. Then comes C, which makes extending records hard to do without casting and macros. Then C++, which offers insane ways of extending them (virtual base classes, multiple inheritance, mixins using templates, ...). Then to make software components more loosely coupled and maintainable, Corba & COM enters the picture, and you only use interfaces to communicate with other objects. Of course COM uses reference counting, so reusable components is actually just an illusion; in order to avoid memory leaks, you need to know how objects are connected, which depends on the implementation... In the meantime Java becomes a succes. Java is basically "back to basics": it tries to address some of the flaws of complicated OO, has garbage collection, promises multi-platform caps, and it is very easy to understand, so people embrace it. Then C# comes along, which initially is almost the same as Java, except is has closures, but it evolves towards a functional language with side effects (even Haskell's FRP will be available in .NET 4.0, with the Rx framework!). Then to manage large and complicated software, things like "dependency injection" and "inversion of control" are introduced, and... we're basically back to COM in a sense, but now with garbage collection.

So I have the impression that OO is running in circles, and every iteration tries to pick up some goodies of the previous one, but where will it end?

Luckily humans seem to have the ability to get things done, whatever primitive or flawed tools we get. I guess the brain itself it the best programming language ;)

Looking at this from a feedback circuit perspective, it seems like that industrial programming is just swinging back and forth between two extremes. It appears that at every step someone runs into the limitations of doing things one way and finds a way to orthogonally combine other designs together. For example, there's been alot of work on implementing other languages on top of Java, such as Jython, so different programming methods can be mixed into enterprise Java code. It all swings back and forth because more than one design and paradigm is needed and no single language can really support it all at once.

-Yaakov Nemoy _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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