Re: [boost] Temporary objects

Subject: Re: [boost] Temporary objects
From: Thomas Klimpel (Thomas.Klimpel_at_[hidden])
Date: 2009-10-31 11:37:20

Mathias Gaunard wrote:
> Thomas Klimpel wrote:
> > What I really would like for the move-proposal is to allow implementing the move-assignment operator as a simple swap
> 
> Testing shows that this is suboptimal and can hurt performance
> significantly.

You probably want to say that implementing "a = std::move(b)" as

tmp.members = a.members
a.members = b.members
b.members = tmp.members

is significantly slower than implementing it as

a.members = b.members

I believe this without testing. What I'm talking about is that the move-assignment operator of the proposed boost::container::vector is implemented for good reasons as

   vector& operator=(BOOST_RV_REF(vector) x)
   {
      if (&x != this){
         this->swap(x);
         x.clear();
      }
      return *this;
   }

and it would be nice if it would be allowed to implement it as

   vector& operator=(BOOST_RV_REF(vector) x)
   {
      this->swap(x);
      return *this;
   }

However, I accepted that "it would be nice" won't come reality, because the good reasons are just too good (with the otherwise required language change as final word).

Regards,
Thomas