Java Closures: first prototype を見て2

http://gafter.blogspot.com/2007/10/java-closures-first-prototype.html

昨日の続き

カリー化

// This work is Copyright(c) 2007 Neal M Gafter.  All rights reserved.
/*
 * @test  /nodynamiccopyright/
 * @summary Test capturing variables from closures
 * @author gafter
 *
 * @clean Clarkson5
 * @compile -source 7 Clarkson5.java
 * @run main Clarkson5
 */

public class Clarkson5 {
    public static <T,U,R> {T=>{U=>R}} curry(final {T,U=>R} f) {
    return {T t=>{U u=>f.invoke(t,u)}};
    }
    public static void main(String[] args)
    {
    {Integer,Integer=>Integer} plus1 = {Integer x, Integer y => x+y};
    {Integer=>{Integer=>Integer}} plus2 = curry(plus1);
    int x1 = plus1.invoke(1, 2);
    int x2 = plus2.invoke(1).invoke(2);
    if (x1 != 3 || x2 != 3) throw new AssertionError(x1 + " " + x2);
    }
}

インタフェースが勝手に実装される？？

// This work is Copyright(c) 2007 Neal M Gafter.  All rights reserved.
/*
 * @test  /nodynamiccopyright/
 * @summary Test the closure conversion and accessing unmodified locals in a closure
 * @author gafter
 *
 * @clean ClosureConversion2
 * @compile -source 7 ClosureConversion2.java
 * @run main ClosureConversion2
 */

import java.util.concurrent.Callable;

public class ClosureConversion2 {
    interface I1<T> {
    T f(T t);
    }
    public static void main(String[] args) {
    System.out.println(g({ String s => "<" + s + ">" }).f("foo"));
    }
    static <T> I1<T> g(I1<T> i) {
    return i;
    }
}

なんでCallable を importしてるのはなんでだろ。

closure と関係ないやつ

// This work is Copyright(c) 2007 Neal M Gafter.  All rights reserved.
/*
 * @test  /nodynamiccopyright/
 * @summary Test disjuntive exception types
 * @author gafter
 *
 * @clean DisjunctiveType1
 * @compile -source 7 DisjunctiveType1.java
 * @run main DisjunctiveType1
 */

public class DisjunctiveType1 {
    interface A {
        void f();
    }
    static class X0 extends Exception {
    }
    static class X1 extends X0 implements A {
        public void f() { System.out.println("one"); }
    }
    static class X2 extends X0 implements A {
        public void f() { System.out.println("two"); }
    }
    public static void main(String[] args) {
        for (int i=0; i<3; i++) {
            try {
                switch (i) {
                case 0: throw new X1();
                case 1: throw new X2();
                case 2:
                    System.out.println("three!");
                }
            } catch (X1|X2 ex) {
                ex.f();
            }
        }
    }
}

たまに欲しいと思ったことはある。

null にキャスト

// This work is Copyright(c) 2007 Neal M Gafter.  All rights reserved.
/*
 * @test  /nodynamiccopyright/
 * @summary Test that we don't allow casting to null
 * @author gafter
 *
 * @clean Null1
 * @compile/fail -source 7 Null1.java
 */
public class Null1 {
    public static void main(String[] args) {
    null x = (null) args;
    }
}

なんじゃこりゃ