[fpc-pascal] Licensing issue: Subclassing

Florian Klaempfl florian at freepascal.org
Tue Jul 27 15:25:16 CEST 2010

Am 27.07.2010 14:32, schrieb Vladimir Zhirov:
> So this seems unclear whether application that subclasses from
> RTL/FCL/LCL is a derived work of RTL/FCL/LCL and must itself be
> licensed under Modified LGPL, making source code open.
> BTW, LGPL v3 explicitly allows subclassing:
> "Defining a subclass of a class defined by the Library is deemed a mode
> of using an interface provided by the Library."
> (http://www.gnu.org/licenses/old-licenses/lgpl-2.0.html#SEC3),
> but Modified LGPL is based on LGPL v2.
> I understand that the whole point of Modified LGPL is to allow creating
> closed-source products using FPC/Lazarus. But in the above aspect it
> seems not clear enough.

Well, the point of the Modified LGPL above is not complete: the goal is
also that one has to release changes like bug fixes to the RTL/FCL
sources. So the thumb rule is pretty simple: as long as you use
unmodified rtl/fcl sources/code, you don't have to release any source
code. If you use modified rtl/fcl sources, you've to release the patches
to the rtl/fcl sources.

> Would someone of the core team please comment on this?

Subclassing a class which is under the modified LGPL used by FPC does
not require to release any sources of the subclasses under the modified

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