相关疑难解决方法(0)

我想知道为什么给定代码的输出(在LinqPad中执行它)

void Main() {
    Compare1((Action)Main).Dump();
    Compare2(Main).Dump();
}

bool Compare1(Delegate x) {
    return x == (Action)Main;
}

bool Compare2(Action x) {
    return x == Main;
}

总是:

 False
 True

我天真地预计它会出现True在两种情况下.

==委托类型的两个表达式之间的重载解析的准确规则是什么？

请考虑以下代码(using System;需要的地方):

static class ProgramA
{
    static void TargetMethod(object obj)
    {
    }

    static void Main()
    {
        Action<object> instance1 = TargetMethod;
        Action<object> instance2 = TargetMethod;

        Action<string> a1 = instance1;
        Action<Uri> a2 = instance2;

        Console.WriteLine((object)a1 == (object)a2);
        Console.WriteLine((Delegate)a1 == (Delegate)a2);
        Console.WriteLine((Action<object>)a1 == (Action<object>)a2);

        Console.WriteLine(a1 == a2);  // warning CS0253: Possible unintended reference comparison; to get a value comparison, cast the right hand side to type 'System.Action<string>'
    }
}

说明:

instance1并且instance2是同一运行时类型的两个独立实例,泛型Action<in T>是逆变的 …