[Too]

Lesson learned from c++ "rule of five"? Where if you implement a destructor you must also carefully implement a copy constructor so that the two copies of the object don't accidentally refer to each others members in any way. Something that is much harder than it sounds like, leading to the now more recommended "rule of zero" saying just don't.

[masklinn]

Rust doesn't have copy constructors per-se (it really doesn't have ctors in he C++ sense). Copy is a "marker trait", its operation can not be overridden and is always (semantically) a simple memcpy. The truth is that Copy is not a thing at runtime, it's only a compile-time restriction (when not present).

Clone would be what comes closest to copy constructors, and it has to be explicitly invoked.

[Tuna-Fish]

Rust doesn't have copy constructors. By hard rule, any normal (non-Pin) rust struct can be safely moved by doing a memcopy of it's storage to a different, correctly aligned memory location. Structs that are Pin just can't be moved at all. Implementing Copy is just a marker that means that after doing the memcopy, the original can still be safely used.

This rule really helps both the compiler and the programmer to make moving and copying things effortless. It does prevent things like a struct holding internal pointers to it's own state. This is not bad on x86, because you can replace internal pointers with internal offsets, and the instruction set contains a fast reg+reg addressing mode, but can cost an extra instruction on many other cpu architectures. IMHO the rule is well worth it, although it is an example of a situation where Rust chooses to give away a bit of performance for sanity.