Re: [patch] : Add move symantics to more of libstdc++

[chris jefferson <caj at cs dot york dot ac dot uk>]

Paolo Carlini wrote:

> chris jefferson wrote:
>
>  
>
> > This patch makes remove, remove_if, rotate and the heap functions move
> > aware. It also tidies up some swaps to iter_swap, and adds a test case
> > or two and a couple of testcases fixes. Has been carefully designed so
> > that it will have no effect on the performance of non move-aware types
> > (in particular the built in types).
> >
> > This patch does do a number of small things at the same time, if you'd
> > like it splitting into patches which each only do one thing, I'll do that.
> >    
>
> I think it's rather understandable as-is, thanks. I'm going to look into
> it, regtest again on my side, and so on. I'll let you know how it goes
> and in case everything is ok, we can go ahead, as usual.
>
> Two quick comments:
> 1- ALISING should be intended as ALIASING, right?
>  
Yup :)

> 2- I have a rough list of algorithms which can internally exploit
> efficient moves (courtesy of Howard Hinnant ;). I would guess the same
> is true for our simulated move-semantics, as far as containers of
> containers are concerned:
> - remove
> - unique (done!)
> - rotate (done!)
> - sort
> - stable-sort
> - heap-sort
> - partition (done!)
>
>  
I've been checking with my own work against n1771, which lists the 
suggested requirements for each algorithm. I agree with them :)

Partition in fact only uses swap, so it was already optimised. Remove is 
also done with this new submission, as is heap sort. The main work left 
revolves around the merging and sorting algorithms, which all use each 
other and the same set of internal algorithms . This requires a) 
move-aware allocators (which aren't actually very hard) and figuring out 
how to change __unguarded_partition without causing a loss of efficency 
for other types.

Once this is done (and in particular the move-aware allocators), then it 
should be easy to also fix the containers themselves (ie reallocating 
deque and vector).

Chris