Re: Why doesn't iter_swap use swap?

[Phil Edwards <phil at codesourcery dot com>]

On Mon, Aug 23, 2004 at 03:36:27PM -0600, Martin Sebor wrote:
> chris wrote:
> 
> >One reason discussed in the standard about why not to use swap() is that 
> >iter_swap may work in some places where swap() doesn't (vector<bool> is 
> >mentioned). I'm not an expert on this, but we seem to in general require 
> >"normal assignment" in for example __unguarded_linear_insert, and other 
> >places.
> 
> The "new" iter_swap will also not work in cases where the two
> iterators' value_types are distinct types:
> 
>     int i;
>     double d;
>     std::iter_swap (&i, &d);

chris and I discussed this on #c++ briefly.  Code like this generates
warnings already.  Our iter_swap implementation does convertibility testing
when concept checks are on, but only a simple assignment of the values.
There's no attempt at, e.g., typecasting.  (Nor do I think there should be.)
So I feel this shouldn't hold back anything.

Is there real-world code which exploits this capability?  We also talked
about that, and nobody could think of any offhand.

I like the idea of requiring that the types be the same, in order to permit
iter_swap to use swap.  We'd also need to add appropriate specializations
and overloads to handle things like list iterators properly.


-- 
Behind everything some further thing is found, forever; thus the tree behind
the bird, stone beneath soil, the sun behind Urth.  Behind our efforts, let
there be found our efforts.
              - Ascian saying, as related by Loyal to the Group of Seventeen