* needed, use {@code function::apply}.
 *
 * <p>This interface is now a legacy type. Use {@code java.util.function.Function} (or the
 * appropriate primitive specialization such as {@code ToIntFunction}) instead whenever possible.
 * Otherwise, at least reduce <i>explicit</i> dependencies on this type by using lambda expressions
 * or method references instead of classes, leaving your code easier to migrate in the future.
 *