람다와 인터섹션 타입을 이용한 동적인 기능확장법

IntersectionType.java

import java.util.function.Consumer;
import java.util.function.Function;

/**
 * @see <a href="https://www.youtube.com/watch?v=PQ58n0hk7DI">토비의 봄 TV 4회 (2) Generics에서 와일드카드 활용법, 람다와 인터섹션 타입을 이용한 동적인 기능확장법</a>
 */
public class IntersectionType {
	interface Pair<T> {
		T getFirst();
		T getSecond();
		void setFirst(T first);
		void setSecond(T second);
	}

	static class Name implements Pair<String> {
		private String firstName;
		private String lastName;

		public Name(String firstName, String lastName) {
			this.firstName = firstName;
			this.lastName = lastName;
		}

		@Override
		public String getFirst() {
			return this.firstName;
		}

		@Override
		public String getSecond() {
			return this.lastName;
		}

		@Override
		public void setFirst(String first) {
			this.firstName = first;
		}

		@Override
		public void setSecond(String second) {
			this.lastName = second;
		}
	}

	interface ForwardingPair<T> extends DelegateTo<Pair<T>>, Pair<T> {
		default T getFirst() { return delegate().getFirst(); }
		default T getSecond() { return delegate().getSecond(); }
		default void setFirst(T first) { delegate().setFirst(first); }
		default void setSecond(T second) { delegate().setSecond(second); }
	}

	interface DelegateTo<T> {
		T delegate();
	}

	private static <T extends DelegateTo<S>, S> void run(T t, Consumer<T> consumer) {
		consumer.accept(t);
	}

	interface Convertable<T> extends DelegateTo<Pair<T>> {
		default void convert(Function<T, T> mapper) {
			Pair<T> pair = delegate();
			pair.setFirst(mapper.apply(pair.getFirst()));
			pair.setSecond(mapper.apply(pair.getSecond()));
		}
	}

	interface Printable<T> extends DelegateTo<Pair<T>> {
		default void print() {
			System.out.println(delegate().getFirst() + " " + delegate().getSecond());
		}
	}

	public static void main(String[] args) {
		Pair<String> name = new Name("Lewis", "John");
		run((ForwardingPair<String> & Convertable<String> & Printable<String>)() -> name, o -> {
			o.print(); // Lewis John

			o.convert(String::toUpperCase);
			o.print(); // LEWIS JOHN

			o.convert(s -> s.substring(0, 2));
			o.print(); // LE JO
		});
	}
}