You’re right that classes exemplify declaring requirements upfront; the GP is limiting scope to what happens at compile time. Taking an argument of class Bar ty

You’re right that classes exemplify declaring requirements upfront; the GP is limiting scope to what happens at compile time. Taking an argument of class Bar typically means taking pointers at runtime to a subclass’ method implementations. Of course, optimizing compilers (especially JITs) can often devirtualize these anyway, so it’s not even that clear-cut.