Re: [boost] [thread] Conformance with N2497 move semantics

Subject: Re: [boost] [thread] Conformance with N2497 move semantics
From: Anthony Williams (anthony.ajw_at_[hidden])
Date: 2008-11-14 07:44:21

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

> N2497 includes the following thread constructor overloadings
>    template <class F> explicit thread(F f);
>    template <class F, class ...Args> thread(F&& f, Args&&... args);
>    void swap(thread&&);
>
> Boost.Threads try to conforms to N2497 as muh as
> possible. Boost.Threads defines already
>
> #ifdef BOOST_HAS_RVALUE_REFS
> template <class F> thread(F&& f);
> #else
> #ifdef BOOST_NO_SFINAE
> template <class F> explicit thread(F f);
> #else
> template <class F>explicit thread(F f,
>        typename disable_if<
>            boost::is_convertible<F&, detail::thread_move_t<F> >,
>                dummy* >::type=0);
> #endif
> template <class F>explicit thread(detail::thread_move_t<F> f);
> template <class F,class ...Args> thread(F f, Args... args)
>
> I have some questions.
> Is there any deep raison for which
>    template <class F> explicit thread(F f);
> should not always  be defined?

It causes problems with the move semantics emulation, being a better
match in some cases and causing additional copies.

> Is there any deep raison to emulate
>    template <class F,class ...Args> thread(F f, Args... args)
> instead of
>    template <class F,class ...Args> thread(F&& f, Args... args)

The former is easier.

> Could
>    template <class F, class ...Args> thread(F&& f, Args&&... args);
> rally be emulated?

Only with a myriad of overloads.

> You provide  'void swap(thread&)'. Could  'void swap(thread&&)' be emulated?

Yes. I thought it was there :-(

> Do you know if the following overloadings are taken in account by the
> boost::swap utility?
>    void swap(thread&  x, thread&  y);
>    void swap(thread&& x, thread&  y);
>    void swap(thread&  x, thread&& y);

No, I don't.

Anthony
-- 
Anthony Williams
Author of C++ Concurrency in Action | http://www.manning.com/williams
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