'委托'System.Action' 不接受 0 个参数.这是 C# 编译器错误(lambdas + 两个项目)吗? [英] 'Delegate 'System.Action' does not take 0 arguments.' Is this a C# compiler bug (lambdas + two projects)?

问题描述

考虑下面的代码.看起来完全有效的 C# 代码对吗?

Consider the code below. Looks like perfectly valid C# code right?

//Project B
using System;
public delegate void ActionSurrogate(Action addEvent);
//public delegate void ActionSurrogate2();
// Using ActionSurrogate2 instead of System.Action results in the same error
// Using a dummy parameter (Action<double, int>) results in the same error

// Project A
public static class Class1 {
    public static void ThisWontCompile() {
        ActionSurrogate b = (a) =>
                            {
                                a(); // Error given here
                            };
    }
}

我收到编译器错误Delegate 'Action' 不接受 0 个参数."在指定位置使用(Microsoft)C# 4.0 编译器.请注意，您必须在不同的项目中声明 ActionSurrogate 才能显示此错误.

I get a compiler error 'Delegate 'Action' does not take 0 arguments.' at the indicated position using the (Microsoft) C# 4.0 compiler. Note that you have to declare ActionSurrogate in a different project for this error to manifest.

变得更有趣了:

// Project A, File 1
public static class Class1 {
    public static void ThisWontCompile() {
        ActionSurrogate b = (a) => { a(); /* Error given here */ };
        ActionSurrogate c = (a) => { a(); /* Error given here too */ };
        Action d = () => { };
        ActionSurrogate c = (a) => { a(); /* No error is given here */ };
    }
}

我是不是在这里偶然发现了一个 C# 编译器错误?

Did I stumble upon a C# compiler bug here?

请注意，对于喜欢使用 lambdas 并试图创建数据结构库以供将来使用的人来说，这是一个非常烦人的错误......(我)

Note that this is a pretty annoying bug for someone who likes using lambdas a lot and is trying to create a data structures library for future use... (me)

删除了错误的案例.

我复制并精简了我的原始项目以实现这一目标.这就是我新项目中的所有代码.

I copied and stripped my original project down to the minimum to make this happen. This is literally all the code in my new project.

推荐答案

这可能是类型推断的问题，显然编译器将 a 推断为 Action 而不是 Action(它可能认为 a 是 ActionSurrogate，它适合 Action>签名).尝试明确指定 a 的类型:

This probably is a problem with type inferance, apperently the compiler infers a as an Action<T> instead of Action (it might think a is ActionSurrogate, which would fit the Action<Action>> signature). Try specifying the type of a explicitly:

    ActionSurrogate b = (Action a) =>
                        {
                            a();
                        };

如果不是这种情况 - 可能会检查您的项目是否有任何采用一个参数的自定义Action 委托.

If this is not the case - might check around your project for any self defined Action delegates taking one parameter.

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