Re: [boost] Composing non copyable and movable classes

Subject: Re: [boost] Composing non copyable and movable classes
From: Vicente Botet (vicente.botet_at_[hidden])
Date: 2008-12-07 07:40:30

----- Original Message ----- 
From: "Mathias Gaunard" <mathias.gaunard_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Saturday, December 06, 2008 11:00 PM
Subject: Re: [boost] Composing non copyable and movable classes

> 
> vicente.botet wrote:
> 
>> The question is how to make X movable efficiently. The first way is to move each one of the movable objects one by one. This could be expensive if the number of members is high. In addition X can have also member that are not movable.
>> 
>> The second approach is to use the same technique, store a pointer to the data on a shared_pointer, and move on one operation all the members via the pointer. 
> 
> Why shared_ptr? There is no sharing of ownership required.
> Just use std::unique_ptr.

Right, std::unique_ptr is enough. 
 
>> I think that this separation is in line with the C++ principle "you don't pay for what you don't use". Any thoughts?
> 
> You're just stating the advantages and disadvantages between storing the 
> data in the object itself and storing it in a separate object that is 
> referenced.
> 
> It's simply a tradeoff between {locality, compactness, allocation speed} 
> and moving speed.

If both classes were available, will you use the class Ci in contexts where nonmovable_Ci is more performant?

Vicente