If you _dont_ license your code under the GPL or some similar license which explicitly allows others to build on your code, copyright prohibits anyone from doing so.
You can't, in general, "create a work that makes use of" somebody else's song, or movie, or novel. Because copyright says you need their permission, and there's not a culture of songwriters, filmmakers, or authors; who explicitly grant the freedom to use their work without asking. I find it difficult to understand people who intentionally use negative language like "viral" about the GPL. It's remarkable there so much high quality software available where the authors have said "here, you can use it inspite of the fact that it's copyrighted to us, the only condition we require is that you offer that freedom to everybody else if you build something new using our copyrighted work."
By that argument, MIT is even more free. Licensing your code under MIT basically says "here, you can use it inspite of the fact that it's copyrighted to us, no strings attached. Go forth and multiply." This is why the GPL gets portrayed as viral. It spreads to the parts that I add and restricts the license for my additions. Don't get me wrong: It's a completely fair thing to do - the authors are giving me something for free, but it's still a restriction.
If you _dont_ license your code under the GPL or some similar license which explicitly allows others to build on your code, copyright prohibits anyone from doing so.
You can't, in general, "create a work that makes use of" somebody else's song, or movie, or novel. Because copyright says you need their permission, and there's not a culture of songwriters, filmmakers, or authors; who explicitly grant the freedom to use their work without asking. I find it difficult to understand people who intentionally use negative language like "viral" about the GPL. It's remarkable there so much high quality software available where the authors have said "here, you can use it inspite of the fact that it's copyrighted to us, the only condition we require is that you offer that freedom to everybody else if you build something new using our copyrighted work."