A program that contains no derivative of any portion of the Library, but is designed to work with the Library by being compiled or linked with it, is called a "work that uses the Library". Such a work, in isolation, is not a derivative work of the Library, and therefore falls outside the scope of this License.
By falling outside the scope of the license, the LGPL isn't viral in the way the GPL is. Code you write can use an LGPL licensed library but be licensed differently itself.
However, you (the developer) are still subject to various legal requirements if you make use of an LGPL licensed library! If you fail to meet those requirements (basically, allow relinking against a modified version of the library) then you are in violation of the license and (in most jurisdictions) subject to penalty under copyright law.
> However, linking a "work that uses the Library" with the Library creates an executable that is a derivative of the Library (because it contains portions of the Library), rather than a "work that uses the library". The executable is therefore covered by this License. Section 6 states terms for distribution of such executables.
When a "work that uses the Library" uses material from a header file that is part of the Library, the object code for the work may be a derivative work of the Library even though the source code is not. Whether this is true is especially significant if the work can be linked without the Library, or if the work is itself a library. The threshold for this to be true is not precisely defined by law.
That certainly does have consequences for what you can do with the software - the object code of your compiled program will include parts of the library.
As far as I understand it, proprietary code using an LGPL licensed library is more or less incompatible with templates in header files (!!!) since there's no way (AFAIK?) to relink against a modified version without providing your full source code. Supposedly the LGPLv3 provides an exception for header files but personally I wouldn't go anywhere near it because it seems quite vague - "small" macros, templates that are less than 10 lines (what constitutes a line?) etc.
So as currently licensed (LGPL), I don't think your library is usable as part of a proprietary project.
The MPL, in contrast, places no relinking requirements on the developer. You only have to share any changes you happen to make to the MPL licensed code.
Ask anybody who actually contributes, usefully, what they think. Their opinion might mean something.
Sometimes LGPL is chosen out of confusion, sometimes symbolically. Whatever the legal demands it does not impose, it would be rude not to honor its intent.
