32 Thread support library [thread]

32.9 Futures [futures]

32.9.2 Header <future> synopsis [future.syn]

namespace std { enum class future_errc { broken_promise = implementation-defined, future_already_retrieved = implementation-defined, promise_already_satisfied = implementation-defined, no_state = implementation-defined }; enum class launch : unspecified { async = unspecified, deferred = unspecified, implementation-defined }; enum class future_status { ready, timeout, deferred }; template<> struct is_error_code_enum<future_errc> : public true_type { }; error_code make_error_code(future_errc e) noexcept; error_condition make_error_condition(future_errc e) noexcept; const error_category& future_category() noexcept; class future_error; template<class R> class promise; template<class R> class promise<R&>; template<> class promise<void>; template<class R> void swap(promise<R>& x, promise<R>& y) noexcept; template<class R, class Alloc> struct uses_allocator<promise<R>, Alloc>; template<class R> class future; template<class R> class future<R&>; template<> class future<void>; template<class R> class shared_future; template<class R> class shared_future<R&>; template<> class shared_future<void>; template<class> class packaged_task; // not defined template<class R, class... ArgTypes> class packaged_task<R(ArgTypes...)>; template<class R, class... ArgTypes> void swap(packaged_task<R(ArgTypes...)>&, packaged_task<R(ArgTypes...)>&) noexcept; template<class F, class... Args> [[nodiscard]] future<invoke_result_t<decay_t<F>, decay_t<Args>...>> async(F&& f, Args&&... args); template<class F, class... Args> [[nodiscard]] future<invoke_result_t<decay_t<F>, decay_t<Args>...>> async(launch policy, F&& f, Args&&... args); }
The enum type launch is a bitmask type ([bitmask.types]) with elements launch​::​async and launch​::​deferred.
[Note 1:
Implementations can provide bitmasks to specify restrictions on task interaction by functions launched by async() applicable to a corresponding subset of available launch policies.
Implementations can extend the behavior of the first overload of async() by adding their extensions to the launch policy under the “as if” rule.
— end note]
The enum values of future_­errc are distinct and not zero.