Re: libstdc++/3552: missing hash function for std::string

[Goswin Brederlow <goswin.brederlow@student.uni-tuebingen.de>]

The following reply was made to PR libstdc++/3552; it has been noted by GNATS.

From: Goswin Brederlow <goswin.brederlow@student.uni-tuebingen.de>
To: Phil Edwards <phil@jaj.com>
Cc: Vadim Ogranovich <vograno@arbitrade.com>,
	  "'goswin.brederlow@student.uni-tuebingen.de'" <goswin.brederlow@student.uni-tuebingen.de>,
	  "'gcc-gnats@gcc.gnu.org'" <gcc-gnats@gcc.gnu.org>,
	  "'Laurent.Bonnaud@inpg.fr'" <Laurent.Bonnaud@inpg.fr>,
	  "'87063-quiet@bugs.debian.org'" <87063-quiet@bugs.debian.org>,
	  "'gcc-bugs@gcc.gnu.org'" <gcc-bugs@gcc.gnu.org>
Subject: Re: libstdc++/3552: missing hash function for std::string
Date: 08 May 2002 19:01:45 +0200

 Phil Edwards <phil@jaj.com> writes:
 
 > On Sat, Apr 27, 2002 at 02:37:52PM -0500, Vadim Ogranovich wrote:
 > > Hi, I independently came across this bug. It seems like it was classified as
 > > not a bug with no workaround posted. Is that the case? Thanks, Vadim
 
 Actually the bug was more on the line that the STL _does_ guess for
 char* but not for string and that it should use the char* hash
 function for strings too.
 
 > Yes.  How can we possibly guess what a good hash function would be for
 > arbitrary strings?  Efficiency of hashing is extremely dependant on the
 > data being hashed.  You need to write one that's appropriate for your data;
 > this will involve multiple experiments.
 > 
 > There is std::collate::hash() for char*'s, but this is essentially a
 > generic guess, and should only be used when you haven't yet had the time
 > to come up with a more appropriate function.
 
 Having one for char* but not for string is a bit of a contradiction.
 
 MfG
         Goswin