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Comment by kccqzy

2 months ago

Deep copy is pedagogically and semantically the right choice for any mutable containers. You either make containers immutable or copies deep. Otherwise it's just an invitation for subtle bugs.

14 comments

kccqzy

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criemen  2 months ago

I'm not sure about that - every time I copy an object I have to think through what happens, no matter the default semantics. C++ makes the deep copy case easier than other programming languages without top-level built-in support.

hgomersall  2 months ago

No, it should move properly when passing by value (as in, essentially the rust move semantics). If you want a copy, that should be explicit.

  • hyghjiyhu  2 months ago

    Moving by default would be too much of a footgun without a borrow checker imo.

    • hgomersall  2 months ago

      I think using a language without a borrow checker is already a massive footgun (albeit less of one for GC/RC languages). More sensible move semantics would still be a big ergonomic improvement.

    • kccqzy  2 months ago

      I think the language allowing use-after-move is honestly a smaller footgun than allowing using uninitialized memory or use-after-free. C++ already has the latter.

vlovich123  2 months ago

Then explain that const isn’t deep and a const container can end up mutating state? Pretending like c++ has a consistent philosophy is amusing and pretending this happened because of pedagogy is amusing. It happened because in c assignment is a copy and c++ inherited this regardless of how dumb it is as a default for containers.

  • kccqzy  2 months ago

    In C++ regular types have the property that const is deep. If you have a const std::vector<int> the you can't modify any of the integers contained in this container. Naturally for flexibility reasons not all types are regular, pointers being the prominent exception, and things like std::string_view being modern examples of non-regular types.

    • vlovich123  2 months ago

      I feel like you could benefit from watching Scott Meyers about the silliness in C++ if you feel like there’s a consistent and logical feel to the language. A lot of this is c++-isms masquerading sensible ideas through official terms (regular and non-regular types)

      3 replies →

cjfd  2 months ago

It certainly makes things easier. But it also makes some things very, very, very inefficient. I want a list with millions/billions of elements. I want to regularly change one of the elements somewhere in the middle. Good luck with the copying.