Re: [boost] C++03 unique_ptr emulation

Subject: Re: [boost] C++03 unique_ptr emulation
From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2009-01-03 15:16:48

Howard Hinnant wrote:
> On Jan 2, 2009, at 6:45 PM, Ion Gaztañaga wrote:
> 
>> I've seen that move emulation is done using a conversion operator (I 
>> think Boost.Thread uses the same technique), is that mechanism the 
>> best way to achieve this?
> 
> It is my current best effort. :-\  It does not have the move-from-const 
> bug that my previous effort had.  And it does not require clients to be 
> aware of the "rv" or "moved-from" type (which is a characteristic I 
> really like).  In this emulation I've made that type private to 
> emphasize the encapsulation of it from clients wanting to move 
> unique_ptr's.

Ok. For some vector and deque code I've used the is_movable<> trait to 
select move_iterator or just raw pointers for internal copies. Maybe 
this is still necessary with your conversion operator code. Although a 
smart move_iterator could do the job, using raw pointers in those cases 
automatically takes advantage of STL uninitialized_copy/copy functions 
that automatically use memcpy.

> Agreed.  The thing I like about my current effort is that clients see 
> either lvalue or rvalue unique_ptr's (or whatever class you're trying to 
> move-enable) and nothing else.  No moved-from wrappers.  Downsides 
> include the fact that move(unique_ptr) is a friend of unique_ptr - a 
> tight coupling that I would rather not have there.  In C++0X, move is a 
> completely generic std-function, a characteristic not achieved by this 
> emulation.

Well, not a big problem if the emulation works!

Regards,

Ion