Re: [boost] [optional] little addition... optional_move_to?

Subject: Re: [boost] [optional] little addition... optional_move_to?
From: Niels Dekker - mail address until 2010-10-10 (niels_address_until_2010-10-10_at_[hidden])
Date: 2009-03-04 11:49:46

>> Well, we can achieve almost the same in old C++03, by declaring the
>> function as a /member/ of optional<T>.  I'd suggest naming it
>> "optional_move_to", as follows:

Fernando Cacciola wrote:
> Nice one! :)

Thanks  :-)

> I keep wondering whether being member functions, these move_to() and
> swap() need the "optional_" name prefix?

In the case of "optional_move_to", "move_to" is okay to me as well, as 
"move_to" isn't so much "overloaded".  (Although I still think that 
"optional_move_to", or even "conditional_move_to", is more clear.)

> On further thinking, if the optional is an lvalue this would do the
> right thing but will have the wrong name o)

If "move_to" does either swap or assign-to, IMO the name is right, even 
if it moves from an lvalue.

> Or, probably better, a single [optional_]assign_to() that magically
> does one or the other depending on "this" being and lvalue or rvalue
> reference
>
> Something which, btw, in C++0x can actually be properly overloaded:
>
>   template<class U> bool optional<T>::assign_to( U& ) & ;
>   template<class U> bool optional<T>::assign_to( U& ) && ;
>
> This is getting unsurprisingly closer to the initial proposal from
> Arno :)

What about adding a "const" overload as well?  ;-)

  template<class U> bool optional<T>::assign_to( U& ) const & ;

Maybe Ion Gaztañaga's Boost.Move can be of help to emulate move 
semantics in C++03? 
http://svn.boost.org/svn/boost/sandbox/libs/move_semantics/doc/html/index.html

Anyway, for the time being I think that adding optional_move_to(T&) and 
optional_swap(T&) members (as I presented), and optional_assign (by 
Arno) should be sufficient.  And I still wonder if Arno would be happy 
to use optional_move_to, instead of his optional_assign...

  Kind regards, Niels