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Comment by arinlen | Hacker News Reader

> In general, you should know what objects you are sending and receiving, and it shouldn’t be a mystery that requires reinterpreting

You should know what's the interface that you're sending/receiving, but if you're planning on making downcasts then either you're doing something very exotic or you should take a step back and reevaluate what you're doing.

I'm seeing a lot of people in this thread complaining about features being added to C++ that improve developer experience, but barely anyone complaining that shooting yourself in the foot requires making intentional choices to get your feet in front of your guns.

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In school I learned about inheritance, not composition. The usual: base "shape" class, then subclasses triangle, square, circle, etc. Then you can have a collection of "shape"s that know what they are. What I've read online indicates it's the same for most other people (who learned in a formal context, anyway). This way of doing things necessitates downcasting; at some point you're converting shape into a triangle or whatever, to access some specific method it has.

I'm not saying this is the right way of doing things (I don't think so), but many people expect this to be possible to do easily -- and it isn't. For them this is normal and not "something very exotic". I guess this is the source of the misunderstanding and the complaints.

> In school I learned about inheritance, not composition.

And that's perfectly fine, provided that students learn that trying to do downcasts like casting an animal instance to a dog instance is something that in general never made any sense, and more often than not reflects ignorance.

> This way of doing things necessitates downcasting;

Not true. That way of doing things necessitates ignorance of basic concepts across many domains, including basic OO programming in general and C++ in particular. You can't blame the tool of your choice for problems you create out of ignorance and failing to think things through.

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