package collection;

public class SetFactory {

    private SetFactory() { /* don't instantiate */ }

    /**
     * Returns the empty set.
     *
     * @param <T> the element type of the returned set.
     * @return the empty set.
     */
    static <T> Set<T> create() {
        return new EmptySet<T>();
    }

    /**
     * Returns the singleton set containing the specified element.
     *
     * @param element an element (must not be null)
     * @param <T>     the element type of the returned set.
     * @return the singleton set containing the specified element.
     */
    static <T> Set<T> create(T element) {
        return new SingeltonSet<T>(element);
    }

    /**
     * Returns a set containing the specified elements. The specified elements may contain equal elements.
     *
     * @param elems elements of the returned set (may contain equal elements)
     * @param <T>   the element type of the returned set.
     * @return a set containing the specified elements.
     */
    static <T> Set<T> create(T... elems) {
        if (elems.length == 0) return create();
        if (elems.length == 1) return create(elems[0]);
        Set<T> result = create();

        for (T t : elems) {
            result = result.add(t);
        }

        return result;
    }
}