空传播算子和动态变量

问题描述

我一直在研究C#6中的null传播运算符，并试图使其与 dynamic 类型的变量一起使用，但没有成功.考虑下面的代码，它可以编译，但是当将空传播应用于动态对象时，CLR在运行时抛出 AccessViolationException .

I have been looking at the null-propagation operator in C#6 and tried to make it work with the variables of dynamic type but without success.Consider the code below, it compiles but CLR throws AccessViolationException at runtime when the null-propagation is applied to dynamic object.

class SomeType
{
    public object SomeProperty { get; set; }

    static void Main()
    {
        var obj = new SomeType() { SomeProperty = "ABCD" };

        var p1 = ((dynamic)obj).SomeProperty;   //OK, p1 is set to "ABCD"
        var p2 = ((dynamic)obj)?.SomeProperty;  //AccessViolationException

        Console.ReadLine();
    }
}

起初我以为这可能是一个错误，但是后来我想到了 struct s.通常，您不能将?.运算符应用于值类型变量(因为它不能为null).但是您可以将其强制转换为 dynamic ，然后应用运算符.因此，我将 SomeType 更改为 struct ，并得到了相同的异常.

At first I thought that this might be a bug but then I thought about structs. Normally you can't apply ?. operator to a value type variable (because it cannot be null). But you can cast it to dynamic and then apply the operator. So I changed SomeType to be struct and got the same exception.

问题是，由于设计原因，动态变量的空传播总是会引发异常，因为基础对象可能是值类型?

The question is, it is by design that null-propagation for dynamic variables always is going to throw exception because the underlying object may be a value type?

AccessViolationException 还是很丑陋，运行代码时是否得到相同的代码?

The AccessViolationException is pretty ugly anyway, do you get the same one when you run the code?

推荐答案

AccessViolationException几乎总是编译器错误或格式不正确的PInvoke调用.

AccessViolationException is almost always either a compiler bug or a mal-formed PInvoke call.

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