Re: [boost] C++03 unique_ptr emulation

Subject: Re: [boost] C++03 unique_ptr emulation
From: David Abrahams (dave_at_[hidden])
Date: 2009-01-08 14:52:21

on Thu Jan 08 2009, Howard Hinnant <hinnant-AT-twcny.rr.com> wrote:

> On Jan 8, 2009, at 12:42 PM, Ion Gaztañaga wrote:
>
>> is quite problematic for container implementation. With the old emulation (that
>> returned detail::rv<T>) this was possible:
>>
>> class vector
>> {
>>  void push_back(const value_type &);
>>  void push_back(boost::detail::rv<value_type>);
>> }
>
> Is it practical to do this instead?
>
> class vector
> {
>  void push_back(value_type x);  // internally move construct from x
> }
>
> You take a performance hit on lvalue copyable expressions which are expensive to move.
> But it gives you the functionality of:
>
> class vector
> {
>  void push_back(const value_type&);
>  void push_back(value_type&&);
> }
>
> And there is no hit on rvalue expressions (if I recall correctly, it has been a little
> while since I did this survey).
>
> I don't know, but from conversations with Sean, I suspect this is the direction the
> Adobe move emulation took.

IIRC, that is the "first cut" direction it took, but you can do
something uglier and more complex when you want to optimize the
expensive-to-move lvalue copyable expressions.  Take a look at their
container implementations.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com