That is true in theory, but in practice it's not feasible. Even assuming you restrict to trivially copyable types, you either have to have a purely-atomic dupli

That is true in theory, but in practice it's not feasible. Even assuming you restrict to trivially copyable types, you either have to have a purely-atomic duplicate of anything that you want to store, or play games with trying to get a fast atomic memcpy. Unless things have changed a lot in the past two years neither LLVM or GCC do that much optimisation around atomics so this comes with disastrous performance implications as well as overhead battling the standard.