Re: [sigc] Linking dynamically with SigC++ (now rather: License)

[Chris Vine <chris cvine freeserve co uk>]

On Sat, 2007-07-14 at 04:31 +0200, Murray Cumming wrote:
> However, I'm now wondering if maybe a change from LGPLv2 to LGPLv3 would
> be simpler. libsigc++ is licensed under "either version 2 of the
> License, or (at your option) any later version" so changing it to
> "version 3 or later" would be a lot less work.
> 
> I think LGPL3 seems to allow more than 10 lines of template code in
> headers, as long as you say that you are using the library, but I'm not
> completely sure:
> http://www.gnu.org/licenses/lgpl-3.0.html 

Time heals most things.  I think LGPL-3 covers it.  What section 3
appears to require is that where the templated code is more than 10
lines in length, the person distributing the program must provide a copy
of the LGPL/GPL and "Give prominent notice with each copy of the object
code that the Library is used in it and that the Library and its use are
covered by this License" - in other words give recognition that the
library is used, which does not seem to be completely unreasonable.

Although not relevant to this, in section 4 the rules on static linking
also appear to have been made substantially less onerous.  A statically
linked binary may be provided, so long as the "Minimal Corresponding
Source" is provided, which does not include the whole program - but I
would not wish to give an opinion on what it does include (it is stated
to be "the Corresponding Source for the Combined Work, excluding any
source code for portions of the Combined Work that, considered in
isolation, are based on the Application, and not on the Linked
Version").  This can be avoided entirely (as at present) by only linking
the program's object code dynamically.

Since the libsigc++ source files are distributed under a licence
enabling them to be used and copied under "version 2.1 of the License,
or (at your option) any later version", happily this avoids you having
to obtain the consent of every person who has contributed code to
libsigc++ (assuming that they have explicitly or impliedly donated the
code on those terms).  You do not need to change the licence to v3 to
achieve the required result, although you could do so.

Chris