alephzero
Is there going to be multiple memory copies when Packet is constructed using std::string?
https://github.com/alephzero/alephzero/blob/6f81ec985724bad87b04fba44e2a664f272f67a7/src/packet.cpp#L85
The reason why the parameter of the constructor Packet::Packet(std::string payload) doesn't use const & or &&, and uses value passing, even if moving is performed, copying will still occur.
This is standard c++ best practice for accepting a string which needs to be retained. This does the minimum copies necessary. If you pass an lvalue, one copy will be made. If you pass an rvalue, such as with std::move, no copies are performed. It is worse to enumerate constructors for const& and &&. Those will not cover all the cases.
Might be worth looking at https://clang.llvm.org/extra/clang-tidy/checks/modernize/pass-by-value.html
Yes, I used a shorter string length when doing the test, and the compiler was optimized for SSO, so the addresses of several intermediate variables I tested were different
Small-String-Optimization involves storing short strings directly within the string object, rather than a pointer to heap memory. They cannot be effectively moved, and Packet needs to guarantee the lifetime of the string. Thank you for sharing your findings, but the issue tracker here isn't the right place for learning C++. If you have specific questions about alephzero's functionalities, feel free to reach out.