Question

最后一个语句无法编译。请参阅评论以及代码以了解我的问题。

class Test
{
    private static void Foo(Delegate d){}

    private static void Bar(Action a){}

    static void Main()
    {
        Foo(new Action(() => { Console.WriteLine("a"); })); // Action converts to Delegate implicitly

        Bar(() => { Console.WriteLine("b"); }); // lambda converts to Action implicitly

        Foo(() => { Console.WriteLine("c"); }); // Why doesn't this compile ? (lambda converts to Action implicitly, and then Action converts to Delegate implicitly)
    }
}

Answer 1

因为.net编译器不知道将lambda转换为什么类型的委托。它可以是一个Action，也可以是void MyDelegate()。

如果按如下方式进行更改，则应该有效：

Foo(new Action(() => { Console.WriteLine("c"); }));

Answer 2

为什么编译器应该知道如何分两步：来自lambda - ＆gt;行动 - ＆gt;委派？

编译：

class Test
{
    private static void Foo(Delegate d) { }

    private static void Bar(Action a) { }

    static void Main()
    {
        Foo(new Action(() => { Console.WriteLine("world2"); })); // Action converts to Delegate implicitly

        Bar(() => { Console.WriteLine("world3"); }); // lambda converts to Action implicitly

        Foo((Action)(() => { Console.WriteLine("world3"); })); // This compiles
    }
}

lambda - ＆gt;委托不编译

2 个答案: