c++ - Why are std::atomic objects not copyable?

Question

It seems that std::atomic types are not copy constructible or copy assignable. Why?

Is there a technical reason why copying atomic types is not possible? Or is the interface limited on purpose to avoid some sort of bad code?

Answer 1

On platforms without atomic instructions (or without atomic instructions for all integer sizes) the types might need to contain a mutex to provide atomicity. Mutexes are not generally copyable or movable.

In order to keep a consistent interface for all specializations of std::atomic<T> across all platforms, the types are never copyable.