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Comment by js7 | Hacker News Reader

Why should you never try to teach objects as representations of real world things? Just curious.

Not the grandparent, but in my view it distracts from what the code actually needs to do. OOP is a tool to structure code and data. It gives us some useful ways to deal with responsibilities, namespaces, some kinds of polymorphism, etc. We should use it in a pragmatic way, and making a class hierarchy reflect the real world often puts aesthetics above practical considerations.

Isn't it tied together? If a new programmer can't structure their code they can't write it.

You'd be surprised what kids can achieve with little more than global variables, gotos and if statements. Structure speeds things up and prevents stupid mistakes once you understand the basics, but before that point it can be overwhelming. Far more important, in myexperience, is the "programming mindset".

I agree with that. I was just remembering the first OO stuff I was taught. I think it was a person object which we then had to use to create "Bill", "Jane", etc. Constructor set stuff like eye colour, height, etc.

Then we went on to create a dating app where it would retrieve things like "all the people with brown eyes"

Let's put it this way: you are asked to write a program that simulates the behavior of an LCR circuit. Do you create objects to represent the components of the circuit?

That example isn't specified enough to show the problem. It's either too simple or too hard. Since we're talking about a beginner, I'll assume you meant it at too simple. But even then you're assigning it to a person with a reasonably technical background. In which case, the LCR circuit is the object and you are asking for a method.

"the LCR circuit is the object and you are asking for a method"

I think that you still have the wrong abstraction here. If you are looking for a general solution, it should be one that can handle LCR circuits, mass-spring systems, etc., though that is probably too much for an introductory course. My real point is that there is nothing to be gained by modeling circuit components or even circuits as objects -- you do not improve maintainability, you do not encourage code reuse, and you do increase the amount of code that does nothing to solve the problem.

My real point is that there is nothing to be gained by modeling circuit components or even circuits as objects

Then I still find your point unclear. Why would you choose them as an exercise to introduce classes, which is what we were talking about? I agree, it's odd. Mammals and dogs, however, are a concept people can understand. As are windows and doors.

We were? I thought the question was, "Why shouldn't we teach that objects model real-world things?" The answer is that in many cases, the real-world things should not be represented as objects; I gave an example of such a case. If a student is being told that objects model real-world things and has internalized that, then when they are presented with the problem of simulating an LCR circuit, it is very likely that they will do the wrong thing and create classes for circuit components, and a class for circuits as a whole.

Further, "dogs and mammals" or "windows and doors" are extremely contrived examples. The fact that you have to invoke an artificial problem just to illustrate this point should be an indication that you are doing something wrong. On the other hand, simulating an LCR circuit is a real-world problem and one that students will probably be asked to solve as a homework assignment (e.g. in a differential equations course).

Just because some things should not be represented as objects doesn't mean that nothing should.

And mammals and dogs as a concrete example- a metaphor, if you will- is an example of a powerful way to teach abstract ideas, not an indication that something is wrong.

What I would find enlightening is how the mammal-dog relationship fails, not how there is something out there for which the model may not fit.

The problem with 'dog is a mammal' is that there's basically no obvious scenario in which you'd actually be modeling things this way unless you're trying to build some kind of ecosystem simulation or whatever. If you want to teach people, not only what inheritance is but why it's useful, you need to use a situation where inheritance makes things easier.

Here's an example that's visual: You are putting interaction widgets on the screen- they display some text, perhaps some other visual indicator, and have a button or text area or slider or something on them (there are some of each). Your base class has the setup: the window/panel/whatever-your-language-calls it, the place where the text goes, and the place where the variable widget goes. All of these widgets inherit the base class, and only differ in the user response portion. This makes it very easy to change the interaction style.

"My real point is that there is nothing to be gained by modeling circuit components or even circuits as objects"

That directly contradicts how SICP teaches it:

Our computational model of a circuit will be composed of objects that correspond to the elementary components from which the circuit is constructed. (p. 273, 2nd ed.)

Elsewhere they say:

If we have been successful in our system organization, then to add a new feature or debug an old one we will have to work on only a localized part of the system. (p. 217)

... which sounds a lot like the benefits you deny. Do you really think SICP is wrong to teach this way? I don't.

I quoted a more general passage where they introduce object modeling here: https://news.ycombinator.com/item?id=6910292. But it seems striking that you would have brought up circuit simulation as when not to do object modeling, as it is the very domain they use to illustrate the strength of the approach.

I don't know. Do you?

No, because it clutters the code. An LCR circuit is a linear system and should be solved as such; the only objects that would be relevant are those that are related to solving linear systems, and at the beginner level we probably should not be asking people to write such a general purpose solution anyway. If you start representing circuit components as objects you will just create a pile of unnecessary code that does not improve maintainability at all.

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