Proposed resolution:

This wording is relative to the FDIS.

1. Change [futures.promise]/16 as indicated:

   void promise::set_value(const R& r);
   void promise::set_value(R&& r);
   void promise<R&>::set_value(R& r);
   void promise<void>::set_value();
   

   […]

   -16- Throws:

   • future_error if its shared state already has a stored value or exception, or
   • for the first version, any exception thrown by the copy constructor ofconstructor selected to copy an object of R, or
   • for the second version, any exception thrown by the move constructor ofconstructor selected to move an object of R.

2. Change [futures.promise]/22 as indicated:

   void promise::set_value_at_thread_exit(const R& r);
   void promise::set_value_at_thread_exit(R&& r);
   void promise<R&>::set_value_at_thread_exit(R& r);
   void promise<void>::set_value_at_thread_exit();
   

   […]

   -16- Throws: future_error if an error condition occurs.

   • future_error if its shared state already has a stored value or exception, or
   • for the first version, any exception thrown by the constructor selected to copy an object of R, or
   • for the second version, any exception thrown by the constructor selected to move an object of R.

[ 2013-04-20, Bristol ]

Accepted for the working paper

[ 2012, Portland: move to Review ]

Moved to Review by the concurrency working group, with no further comments.

[futures.promise]/16 says that promise::set_value(const R&) throws any exceptions thrown by R's copy constructor, and that promise_set_value(R&&) throws any exceptions thrown by R's move constructor.

[futures.promise]/22 is the Throws: clause for promise::set_value_at_thread_exit. It has no corresponding requirements, only that these functions throw "future_error if an error condition occurs."

Daniel suggests wording to fix this: The approach is a bit more ambitious and also attempts to fix wording glitches of [futures.promise]/16, because it would be beyond acceptable efforts of implementations to determine whether a constructor call of a user-defined type will indeed call a copy constructor or move constructor (in the first case it might be a template constructor, in the second case it might also be a copy-constructor, if the type has no move constructor).