There's no guarantee that std::move moves elements out of x. (and thus no guarantee that it's equivalent to a Rust mem::replace with a new Vec) The only require

There's no guarantee that std::move moves elements out of x. (and thus no guarantee that it's equivalent to a Rust mem::replace with a new Vec) The only requirement the C++ standard imposes is that the vector is left in a "valid but unspecified state".