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std::experi...future::then(3) C++ Standard Libarystd::experi...future::then(3)

NAME
       std::experimental::future::then - std::experimental::future::then

Synopsis
	  template < class F >
	  future</* see	below */> then(F&& func) ;

	  Attach  the continuation func	to *this. The behavior is undefined if
       *this has no
	  associated shared state (i.e., valid() == false).

	  Creates a shared state associated with the future object to  be  re-
       turned, and a copy
	  fd  of  func	constructed as if by DECAY_COPY(std::forward<F>(func))
       evaluated in the
	  thread calling then, where DECAY_COPY	is defined as

	  template <class T>
	  std::decay_t<T> DECAY_COPY(T&& v) {
	      return std::forward<T>(v);
	  }

	  When the shared state	currently associated with *this	is ready,  the
       continuation
	  INVOKE(std::move(fd),	 std::move(*this)) is called on	an unspecified
       thread of
	  execution, where INVOKE is the operation  defined  in	 Callable.  If
       that expression is
	  invalid, the behavior	is undefined.

	  Any  value returned from the continuation is stored as the result in
       the shared state
	  of the returned future object. Any exception propagated from the ex-
       ecution of the
	  continuation is stored as the	exceptional result in the shared state
       of the returned
	  future object.

	  Let U	be the return type of the continuation (i.e.
	  std::result_of_t<std::decay_t<F>(std::experimental::future<T>)>). If
       U is
	  std::experimental::future<T2>	for some type T2, then the return type
       of then is
	  std::experimental::future<T2>,  otherwise  it	  is   std::experimen-
       tal::future<U>. This is
	  known	as implicit unwrapping.

	  If  implicit	unwrapping takes place and the continuation returns an
       invalid future,
	  then the shared state	is  made  ready	 with  an  exception  of  type
       std::future_error with
	  an error condition of	std::future_errc::broken_promise.

	  After	this function returns, valid() is false.

Parameters
	  func - A continuation	to be attached.

Return value
	  A  std::experimental::future object associated with the shared state
       created by this
	  object. valid() == true for the returned object.

Example
	   This	section	is incomplete
	   Reason: no example

http://cppreference.com		  2022.07.31	 std::experi...future::then(3)

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