Re: Implementing clean and simple move symantics

[Gabriel Dos Reis <gdr at integrable-solutions dot net>]

Joe Buck <Joe.Buck@synopsys.COM> writes:

| Joe Buck wrote:
| > [ memmove better than swap for many types ]
| 
| On Wed, Nov 24, 2004 at 11:01:12AM +0000, Chris Jefferson wrote:
| > Hmm.. I'll have to think about this a bit. In actual fact, I think all 
| > of the standard containers look like they can be moved by memmove, and 
| > (quick test program), that is faster even for things like sorting 
| > vectors of vectors and such things. However using memmove involves being 
| > quite careful if its being used for things like sorting, and I suspect 
| > it would be very hard to avoid code duplication (which is what I was 
| > trying to do before). It might simply be unavoidable, in which case 
| > we'll have to live with it :)
| 
| If we specialize for memmove'able types, then clearly we have separate
| code for those types that are not memmove'able.  swap has the advantage
| that it works for everything.  But since swap is 3x worse in many
| situations, I think the price in added complexity is worth paying.

I see that we have a specialization of std::copy() for plain pointer
arguments to use memcpy/memmove, but I have not seen evidence that
such a specialization is faster -- for common cases -- than aligned
access implied by the plain grammar school loop written in the primary
template... 

-- Gaby