What is copy elision and RVO in C++?

When a function returns an object, the compiler can build it directly in the place of the caller, with no copy and no move. This is copy elision. Since C++17 it is guaranteed when you return a temporary (a prvalue). With a named local variable (NRVO) it is allowed, and most compilers do it.

#include <iostream>

struct Noisy {
    Noisy() { std::cout << "construct\n"; }
    Noisy(const Noisy&) { std::cout << "copy\n"; }
    Noisy(Noisy&&) noexcept { std::cout << "move\n"; }
};

Noisy make() { return Noisy(); }                 // guaranteed: no copy, no move

int main() {
    Noisy n = make();
}

So return std::move(local); is a mistake: it can stop the elision. Just write return local;. See Move Semantics.

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