[future.syn]

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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 }; // [futures.errors], error handling 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; // [futures.future.error], class future_error class future_error; // [futures.promise], class template promise 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>; // [futures.unique.future], class template future template<class R> class future; template<class R> class future<R&>; template<> class future<void>; // [futures.shared.future], class template shared_future template<class R> class shared_future; template<class R> class shared_future<R&>; template<> class shared_future<void>; // [futures.task], class template packaged_task 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; // [futures.async], function template async 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]

33 Concurrency support library [thread]

33.10 Futures [futures]

33.10.2 Header <future> synopsis [future.syn]