Re: [patch] std::string::operator[] extension in debug mode

[Douglas Gregor <doug dot gregor at gmail dot com>]

On May 19, 2005, at 3:14 PM, Gabriel Dos Reis wrote:

> Jonathan Wakely <cow@compsoc.man.ac.uk> writes:
>
> | On Thu, May 19, 2005 at 08:04:31PM +0200, Gabriel Dos Reis wrote:
> |
> | > A question I have is why conditionalizing the extern template 
> stuff on
> | > debug does not work.
> |
> | Because the lib was not built with debug, so the extern template
> | instantiation (sans assertions) is always in the lib.
>
> If the lib was not build with debug and user wants to use it as with
> debug support, then user is in trouble he/she asked for.

The libstdc++ debug mode was specifically designed so that there is 
only one version of the compiled libstdc++ library, which may be linked 
with user applications that are compiled with -D_GLIBCXX_DEBUG and 
without (or even mixing code compiled with the different flags). Strong 
using and some tricky namespace work makes this possible. The problem 
is that basic_string<> permeates libstdc++ so much that we can't pull 
the same tricks that we do with, e.g., std::vector.

> |  If you disable
> | extern templates your .o file includes an implicit instantiation 
> (with
> | assertions).
>
> I think I understand that part.
>
> | When you link to the lib you get ODR.
>
> But you don't have to put it in the non-debug lib.
>
> -- Gaby

With respect to -D_GLIBCXX_DEBUG, there is no "debug lib" and 
"non-debug lib"; just one lib that's compiled without _GLIBCXX_DEBUG 
defined.

	Doug