I really do hope we can't copyright a single function signature. But then, you expand it into an entire framework, or the perfectly designed kernel... What is software if not a collection of API calls? There's clearly something worth copyrighting at some point.
I think what it comes down to is it's copyright, but there's an exception for compatibility. Like a 3rd party part in your car. You can't claim it's the other brand's product, but you can claim it's compatible with that brand. It happens all the time, in all industries. So why can't it be the same with software APIs? A copyright exception for "interfaces" sounds like a pretty safe approach.
Unless their's a patent involved preventing someone from recreating a certain process or method, or a trademark preventing confusion, the act of creativity itself cannot be bounded. Copyright gives rights to the creator for their own creation. It can't prevent someone else from trying to create the same thing with their own hands.
I think what it comes down to is it's copyright, but there's an exception for compatibility. Like a 3rd party part in your car. You can't claim it's the other brand's product, but you can claim it's compatible with that brand. It happens all the time, in all industries. So why can't it be the same with software APIs? A copyright exception for "interfaces" sounds like a pretty safe approach.
Unless their's a patent involved preventing someone from recreating a certain process or method, or a trademark preventing confusion, the act of creativity itself cannot be bounded. Copyright gives rights to the creator for their own creation. It can't prevent someone else from trying to create the same thing with their own hands.