url(relativeTo:)

Returns a URL created from the URLComponents relative to a base URL.

iOS
8.0+
macOS
10.10+
tvOS
9.0+
watchOS
2.0+
func url(relativeTo base: URL?) -> URL?

If the URLComponents has an authority component (user, password, host or port) and a path component, then the path must either begin with “/” or be an empty string. If the URLComponents does not have an authority component (user, password, host or port) and has a path component, the path component must not start with “//”. If those requirements are not met, nil is returned.