C++ std::move doesn't move anything: A deep dive into Value Categories
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Re: C++ std::move doesn't move anything: A deep dive into Value Categories
#2I always understood move as moving ownership, so it's not a misnomer.
> std::move is like putting a sign on your object “I’m done with this, you can take its stuff.”
Which exactly is moving ownership.
Re: C++ std::move doesn't move anything: A deep dive into Value Categories
#3I always understood move as moving ownership, so it's not a misnomer. > std::move is like putting a sign on your object “I’m done with this, you can take its stuff.” Which exactly is moving ownership.
Personally I see std::move more like removing ownership because it’s not explicit from its call where the ownership is transferred.
Re: C++ std::move doesn't move anything: A deep dive into Value Categories
#4I always understood move as moving ownership, so it's not a misnomer. > std::move is like putting a sign on your object “I’m done with this, you can take its stuff.” Which exactly is moving ownership.
Std move doesn’t move ownership. It simply casts into something that could have its ownership taken. Whether or not that actually happens is impossible to identify statically and the value after ownership is consumed is unspecified - sometimes it’s UB to access the value again, sometimes it’s not.
Re: C++ std::move doesn't move anything: A deep dive into Value Categories
#5I don’t think this is particularly insightful, as move semantics and r-values are higher level language semantics, nothing more and nothing less.
Rust’s borrow checker doesn’t actually borrow anything either, it’s operating on a similar level of abstraction.
Re: C++ std::move doesn't move anything: A deep dive into Value Categories
#6I always understood move as moving ownership, so it's not a misnomer. > std::move is like putting a sign on your object “I’m done with this, you can take its stuff.” Which exactly is moving ownership.
Std move doesn’t move ownership. It simply casts into something that could have its ownership taken. Whether or not that actually happens is impossible to identify statically and the value after ownership is consumed is unspecified - sometimes it’s UB to access the value again, sometimes it’s not.
May be disown would be more descriptive, but the point is that it's intended for transferring of ownership versus copying data.
Re: C++ std::move doesn't move anything: A deep dive into Value Categories
#7Maybe std::make_movable would have been a slightly better name, but it's so much simpler to write std::move.
Re: C++ std::move doesn't move anything: A deep dive into Value Categories
#8I always understood move as moving ownership, so it's not a misnomer. > std::move is like putting a sign on your object “I’m done with this, you can take its stuff.” Which exactly is moving ownership.
Std move doesn’t move ownership. It simply casts into something that could have its ownership taken. Whether or not that actually happens is impossible to identify statically and the value after ownership is consumed is unspecified - sometimes it’s UB to access the value again, sometimes it’s not.
That's quite inaccurate.
It needs to remain destructible, and if the type satisfies things like (move-)assignable/copyable, those still need to work as well.
For boxed types, it's likely to set them into some null state, in which case dereferencing them might be ill-formed, but it's a state that is valid for those types anyway.
Re: C++ std::move doesn't move anything: A deep dive into Value Categories
#9Naming things is hard.
Re: C++ std::move doesn't move anything: A deep dive into Value Categories
#10The best way to think about it is that std::move is a cast.