Swift throws are results, but now with specific and generic and specializable types. To illustrate, Swift has a nice `rethrows` feature that helps with functio

Swift throws are results, but now with specific and generic and specializable types. To illustrate, Swift has a nice `rethrows` feature that helps with function composition. If your function takes a function parameter that can throw, it can use 'rethrows' to say "I only throw if this parameter does". Then when passed a function that doesn't throw, your function need not be invoked with `try`. This plays nicely with generics over throwing type, since the bounds propagate back to the function type. If the function parameter only throws a given type, that's what the function will throw. Also helpful for reducing error boilerplate, `try` has the convenience form `try?` which means "just swallow the exception and return nil", and applies to a whole chain: `let f = try? this() ?? that() ?? "skip"` means f will be the result of either (throwing) function or a literal otherwise.