some basic_string optimization

[Nathan Myers]

On Fri, Apr 28, 2000 at 07:14:32PM +0400, Vadim Egorov wrote:
> I found that replacing a single character in a string was a bit more 
> expensive than I thought. Making _M_mutate call conditional made
> this operation work seems improves the situation.
>  ...
> diff -c -r1.59 string.tcc
> *** string.tcc	2000/03/28 04:21:42	1.59
> --- string.tcc	2000/04/28 14:30:36
> ***************
> *** 440,446 ****
> ! 	_M_mutate(__off, __dold, __dnew);
> --- 440,447 ----
> !         if (__dold != __dnew)
> !           _M_mutate(__off, __dold, __dnew);

I think this doesn't work.  You must also check that the
string representation isn't shared with any other string
object; see the definition of _M_mutate, and the non-const
operator[].  Is there some reason you're not using operator[]?

Nathan Myers
ncm at cantrip dot org