Java works ...

[yii-iiy]

To fix the generic val unsupported

final var birds = 
new Object() 
{
	<A> Function<A,A> idiot () { return (Function<A,A>) (a -> a) ;}
} ;

birds.idiot().apply(7) ; // 7

method is value.

and, iife, also can use this.

[yii-iiy]

还有这俩也记一下，应该有地方用到

import java.util.HashMap;
import java.util.Map;
import java.util.function.Function;

public class Single {
    private static Map<Class<?>, Object> instances = new HashMap<>();

    public static <T> T instance(Class<T> clazz) throws Exception {
        if (!instances.containsKey(clazz)) {
            instances.put(clazz, clazz.getDeclaredConstructor().newInstance());
        }
        return (T) instances.get(clazz);
    }

    public static <T, R> Function<T, R> memoize(Function<T, R> function) {
        Map<T, R> cache = new HashMap<>();
        return input -> cache.computeIfAbsent(input, function::apply);
    }
}

public class A {
    public String b = "Hello, world!";
}

public class Main {
    public static void main(String[] args) throws Exception {
        System.out.println(Single.instance(A.class).b);  // 输出：Hello, world!

        Function<Integer, Integer> square = x -> x * x;
        Function<Integer, Integer> memoizedSquare = Single.memoize(square);
        System.out.println(memoizedSquare.apply(5));  // 输出：25
    }
}

<T, R> Function<Function<T, R>, Function<T, R>> memoize = <T, R> (
    
    f -> { Map<T, R> memoizes = new HashMap<>(); return input -> memoizes.computeIfAbsent(input, f::apply) ; } ) ;

// err