Re: [boost] [repost] Futures Review - can move_dest_type be public?

Subject: Re: [boost] [repost] Futures Review - can move_dest_type be public?
From: Anthony Williams (anthony.ajw_at_[hidden])
Date: 2009-02-10 12:22:09

"vicente.botet" <vicente.botet_at_[hidden]> writes:

>> Hi,
>> 
>> The function get is defined in the documentation with following prototypes
>> 
>>    R&& unique_future::get();
>>    R& unique_future<R&>::get();
>>    void unique_future<void>::get();
>> 
>> But when the move semantic is emulated this is just translated as 
>> 
>>        move_dest_type get()
>> 
>> with move_dest_type defined depending on the future template parameter as follows
>> 
>>        typedef typename detail::future_traits<R>::move_dest_type move_dest_type;
>> 
>>        template<typename T>
>>        struct future_traits
>>        {
>> #ifdef BOOST_HAS_RVALUE_REFS
>>            typedef T const& source_reference_type;
>>            struct dummy;
>>            typedef typename boost::mpl::if_<boost::is_fundamental<T>,dummy&,T&&>::type rvalue_source_type;
>>            typedef typename boost::mpl::if_<boost::is_fundamental<T>,T,T&&>::type move_dest_type;
>> #else
>>            typedef T& source_reference_type;
>>            typedef typename boost::mpl::if_<boost::is_convertible<T&,boost::detail::thread_move_t<T> >,boost::detail::thread_move_t<T>,T const&>::type rvalue_source_type;
>>            typedef typename boost::mpl::if_<boost::is_convertible<T&,boost::detail::thread_move_t<T> >,boost::detail::thread_move_t<T>,T>::type move_dest_type;
>> #endif
>> 
>>        };
>> 
>> Generic libraries using the futures needs to get the type returned by
>> get. What do you think about making the move_dest_type public at
>> least when BOOST_HAS_RVALUE_REFS is not defined? Another option would
>> be to make public the future_traits class.

That's an interesting idea. I can see the benefit of being able to know
the type of unique_future<T>::get() without having to use
decltype/BOOST_TYPEOF.

Maybe a unique_future<T>::get_result_type typedef would be most
appropriate.

Anthony
-- 
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