Writing an exception to LGPL for a C++ template library

[Federico Montesino Pouzols]

Hi Benoît,

On Wed, Oct 25, 2006 at 12:27:48PM +0200, Benoît Jacob wrote:
> But while we allow unrestricted _use_, we want to only allow _changes_ under 
> the terms of the LGPL, so that back-contribution of changes is forced. This 
> is why we're choosing the LGPL and not the BSD, for instance.

I think what you want here is the following: LGPL-like behavior when
someone is using using your templates as a classical old-good-times C
library, and GPL-like behavior for anything else. I believe the best
option is using GPL + linking exception. I would definitely consider
the exception used in the GCC C++ std. library (and other packages
such as GNU Common C++ and some of its derivatives):

The exception in the GCC C++ std. library is:

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

In Common C++, it is extended and clarified like this:

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.
//
// This exception applies only to the code released under the name GNU
// Common C++.  If you copy code from other releases into a copy of GNU
// Common C++, as the General Public License permits, the exception does
// not apply to the code that you add in this way.  To avoid misleading
// anyone as to the status of such modified files, you must delete
// this exception notice from them.
//
// If you write modifications of your own for GNU Common C++, it is your choice
// whether to permit this exception to apply to your modifications.
// If you do not wish that, delete this exception notice.

HTH.