sbyte []可以神奇地转换为byte [] [英] sbyte[] can be magically cast to byte[]

问题描述

我不确定这是否是.NET错误，但我发现它真的很有趣.

I'm not sure whether this is a .NET bug but I find it really interesting.

按预期，我不能这样做:

As expected, I cannot do this:

sbyte[] sbytes = { 1, 2, 3 };
byte[] bytes = sbytes; // fails: cannot convert source type 'sbyte[]' to taget type 'byte[]'

但是，如果 sbytes 的类型是 object ，则此方法有效:

However, if the type of sbytes is object, this works:

object obj = new sbyte[]{ 1, 2, 3 };
byte[] bytes = obj as byte[];
Assert.IsNull(bytes, "WTF??")

注释1 : int [] - uint [] 和其他原始类型也会发生相同的问题.

Remark 1: The same issue occurs for int[] - uint[] and the other primitive types as well.

注释2 :尽管代码将数组作为 byte [] 处理，但调试器失去了焦点并在其中显示? -s数组.

Remark 2: Though the code handles the array as a byte[], the debugger loses the focus and shows ?-s in the array.

注释3 :这仅适用于数组，不适用于基础类型本身:

Remark 3: This works only for arrays, not for the underlying types themselves:

object sbyteObj = (sbyte)1;
byte byteObj = (byte)sbyteObj; // System.InvalidCastException: Specified cast is not valid.

好的，我当然可以检查这种类型:

Ok, of course I can check the type like this:

if (obj.GetType() == typeof(byte[]))

这是 as 运算符和直接强制转换的预期行为，还是这是.NET错误?

Is this an intended behavior of the as operator and direct casting, or is this a .NET bug?

推荐答案

不，这不是bug.只是C#语言规则(声称没有可用的转换)和CLR规则(其中有 可用的转换)之间的阻抗不匹配.

No, it's not a bug. It's just an impedance mismatch between the C# language rules (which claim there's no conversion available) and the CLR rules (where the conversion is available).

请注意，编译器确实认为自己最了解:

Note that the compiler really, really thinks it knows best:

byte[] bytes = new byte[10];
// error CS0030: Cannot convert type 'byte[]' to 'sbyte[]'
sbyte[] sbytes = (sbyte[]) bytes; 

即使您已经编译了带有警告的代码，它也并没有真正做到上面所说的:

And even when you've got code that compiles with a warning, it doesn't really do what it says:

byte[] bytes = new byte[10];
// warning CS0184: The given expression is never of the provided ('sbyte[]')
if (bytes is sbyte[])
{
    Console.WriteLine("Yes");
}

运行该代码，您不得到输出...但是，如果您只是更改 bytes 的编译时类型，它可以 打印是:

Run that code and you don't get output... but if you just change the compile-time type of bytes, it does print Yes:

object bytes = new byte[10];
// No warning now
if (bytes is sbyte[])
{
    Console.WriteLine("Yes"); // This is reached
}

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