alt Hacker News"interfaces are not copyrightable"
That shorthand rule of thumb is often applicable, but can lead to risky / incorrect assumptions.
The central distinction isn't simply interface versus implementation. It's functional systems and constraints versus protectable expression - a distinction that can cut through both an interface and its implementation.
copyrighting an interface would break anti-trust, as it would mean no competitors can provide their alternative interface implementing products, on either side of the interface.
It would be like patenting a philips screwdriver or screw.