The version without std::move does not call a constructor because of copy elision. The get_display_pixels function constructs the disp_pixels object in place.

The version without std::move does not call a constructor because of copy elision. The get_display_pixels function constructs the disp_pixels object in place. In the version with std::move, it first copy-elides the function call into a temporary, then move-constructs the disp_pixels object from the temporary. ie as if auto tmp = emulator.get_display_pixels(); const auto disp_pixels = std::move(tmp); // move constructor called here // lifetime of tmp ends So the version with std::move is invoking an extra move-constructor and destructor call.