从 this question 简化而来并消除了 LinqPad 可能产生的影响(没有冒犯性)，这是一个像这样的简单控制台应用程序:

public class Program
{
    static void M() { }    
    static void Main(string[] args)
    {
        Action a = new Action(M);
        Delegate b = new Action(M);
        Console.WriteLine(a == b);      //got False here
        Console.Read();
    }        
}

上述代码的 CIL 中的运算符 ceq 导致“false”(有关详细信息，请访问原始问题)。所以我的问题是:

(1) 为什么 == 翻译成 ceq 而不是 call Delegate Equals？

这里我不关心 Delegate 和 Action 之间的(un)wrapping。最后，在评估 a == b 时，a 是 Action 类型，而 b 是 Delegate。来自规范:

7.3.4 Binary operator overload resolution

An operation of the form x op y, where op is an overloadable binary operator, x is an expression of type X, and y is an expression of type Y, is processed as follows:

• The set of candidate user-defined operators provided by X and Y for the operation operator op(x, y) is determined. The set consists of the union of the candidate operators provided by X and the candidate operators provided by Y, each determined using the rules of §7.3.5. If X and Y are the same type, or if X and Y are derived from a common base type, then shared candidate operators only occur in the combined set once.

• If the set of candidate user-defined operators is not empty, then this becomes the set of candidate operators for the operation. Otherwise, the predefined binary operator op implementations, including their lifted forms, become the set of candidate operators for the operation. The predefined implementations of a given operator are specified in the description of the operator (§7.8 through §7.12).

• The overload resolution rules of §7.5.3 are applied to the set of candidate operators to select the best operator with respect to the argument list (x, y), and this operator becomes the result of the overload resolution process. If overload resolution fails to select a single best operator, a binding-time error occurs.

7.3.5 Candidate user-defined operators

Given a type T and an operation operator op(A), where op is an overloadable operator and A is an argument list, the set of candidate user-defined operators provided by T for operator op(A) is determined as follows:

• Determine the type T0. If T is a nullable type, T0 is its underlying type, otherwise T0 is equal to T.

• For all operator op declarations in T0 and all lifted forms of such operators, if at least one operator is applicable (§7.5.3.1) with respect to the argument list A, then the set of candidate operators consists of all such applicable operators in T0.

• Otherwise, if T0 is object, the set of candidate operators is empty.

• Otherwise, the set of candidate operators provided by T0 is the set of candidate operators provided by the direct base class of T0, or the effective base class of T0 if T0 is a type parameter.

从规范来看，a 和 b 具有相同的基类 Delegate，显然应该应用 Delegate 中定义的运算符规则 ==此处(运算符 == 本质上调用 Delegate.Equals)。但是现在看起来用户定义运算符的候选列表是空的，最后 Object == 被应用了。

(2) FCL 代码是否应该(是否)遵守 C# 语言规范？如果不是，我的第一个问题就没有意义，因为有些东西是经过特殊处理的。然后我们可以用“哦，这是 FCL 的特殊待遇，他们可以做我们做不到的事情。该规范是针对外部程序员的，别傻了”来回答所有这些问题。

最佳答案

编译器与委托(delegate)的工作方式非常不同且不寻常。有很多隐式处理。 请注意，本指南中的“通用基本类型”规则适用于“用户定义的运算符”。委托(delegate)是内部的和系统的。例如，您可以编写 Action a = M; 而不是 Action a = new Action(M);。您可以在之后添加 a += M;。看看CIL发生了什么，第一时间很有趣。

此外:比较代表是危险且重要的。每个委托(delegate)实际上都是多播委托(delegate)。您可以将多个函数指针添加到同一个委托(delegate)。委托(delegate) [L(); M(); N();] 等于委托(delegate) [M();] ？函数指针包含类实例(例如方法)。 [a.M();] 是否等于 [b.M();]？这一切都取决于案例，比较实现需要遍历调用列表。

Delegates 从通用基类型 Delegate 继承是隐式的，你可能会在其他场景中遇到这个问题，例如泛型约束:您不能将 Delegate 指定为泛型参数 T 的约束。此处编译器明确拒绝这一点。创建自己的类也是如此，继承自 Delegate。

这是对两个问题的回答——“Delegate”不是纯粹的 FCL，它与编译器紧密耦合。如果您真的想要 Microsoft 的委托(delegate)比较器行为 - 只需显式调用 Equals(a, b)

关于c# - 隐式方法组转换陷阱(第 2 部分)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/8939350/