c# - Delegate.Combine 和 lambda 表达式

Question

假设我有这个委托(delegate)的声明:

    private delegate UInt32 Feedback(UInt32 value);

在这里我尝试将它与 lambda 表达式一起使用

    feedback = (Feedback)Delegate.Combine(feedback, 
        value => { Console.WriteLine("Lambda item = " + value); return 0; });

但我得到错误:无法将 lambda 表达式转换为类型“System.Delegate”，因为它不是委托(delegate)类型

但它是这样工作的

    feedback = (Feedback)Delegate.Combine(feedback, 
        new Func<UInt32, UInt32>(value => { Console.WriteLine("Lambda item = " + value); return 0; }));

我认为 C# 编译器必须自己完成。

Answer 1

feedback = (Feedback)Delegate.Combine(feedback, 
    (Feedback)(value => { Console.WriteLine("Lambda item = " + value); return 0; }));

您必须明确说明 lambda 函数的类型，否则编译器不知道它的类型。例如参见 http://blogs.msdn.com/b/jaredpar/archive/2007/12/14/c-lambda-type-inference.aspx

One of the limitations of C# type inference is that you cannot use it to infer the type of a lambda expression. For example, the following code will not compile

var f = () => 4;