GPL with the Classpath exception - clarification needed

[John Cowan]

Wilson, Andrew scripsit:

> A cautious person would probably prefer, if possible, a license with a
> black-letter permission that use of a class library does not create a
> derivative work subject to the copyleft license of the library itself.

The relevant distinction for LGPL purposes is not whether something is
a derivative work or not: every program that incorporates the library
into itself is a derivative work.  The question is whether the derivative
work is a "work based on the Library" (LGPL 2.1) / "Modified Version of
the Library" (LGPL 3.0) or not.

Now subclassing a class plainly does not *modify* the class.  So programs
that contain subclasses of an LGPLed class, or instantiations of an
LGPLed interface, or what have you, are "works that use the Library"
(LGPL 2.1) / "Applications" (LGPL 3.0) and may be under any license
provided it is possible to replace the library.  In Java, or any language
normally delivered either in source form or in component-by-component
binary form with run-time linkage, this is very easy, meaning that the
LGPL and the GPL+CP are essentially equivalent.  The GPL+CP matters
only for a library written in a language where delivery by way of static
executables is the norm, and replacement would require the proprietary
part of the application to be delivered as .o files or something similar.

-- 
After fixing the Y2K bug in an application:     John Cowan
        WELCOME TO <censored>                   cowan at ccil.org
        DATE: MONDAK, JANUARK 1, 1900           http://www.ccil.org/~cowan