如何优雅地创建一个返回lambda的返回值或什么都不返回的函数? [英] How to elegantly create a function which returns a lambda's return value or nothing?

问题描述

我想用Java编写一个更高阶的函数，该函数需要一个lambda并返回labmda的返回值，或者如果lambda没有返回类型则不返回任何内容.

I want to write a higher order function in Java which takes a lambda and returns the labmda's return value or does not return anything if the lambda has no return type.

在科特林中，我会做类似的事情:

In Kotlin, I would do something like this:

fun <T> test(block: () -> T): T {
    val r = block()
    // ...
    return r
}

由于万一没有返回 的情况下Unit将是T，因此它将起作用.

Since Unit will be T in case nothing is returned, this will work.

在 Java 中，我只能提出以下建议:

In Java I could only come up with this:

public class Main {

    private static <T> T test(Supplier<T> s) {
        T t = s.get();
        // ...
        return t;
    }

    private static void test(Runnable r) {
        // ...
        r.run();
    }

    public static void main(String args[]) {
        test(() -> System.out.println("Hello")); // returns void
        test(() -> 5); // return an Int
    }
}

当我想返回lambda的返回值时，我不得不重载test，如果lambda不返回任何内容，则给它一个Runnable.

I had to overload test giving it a Supplier<T> when I want to return the lambda's return value and a Runnable if the lambda does not return anything.

有没有更好的方法而不过载?

Is there a better way without overloading?

由于void(但Void可以)不能代替T，所以我不知道如何.

Since void (but Void could) cannot take the place of T, I don't see how.

推荐答案

有没有更好的方法而不过载?

Is there a better way without overloading?

否.

您最好的办法是通过从Runnable重载中调用Supplier重载来避免重载中的重复:

The best you can do is to avoid duplication in the overloads, by calling the Supplier overload from the Runnable overload:

private static void test(Runnable r) {
  test(() -> { r.run(); return null; });
}

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