.NET字符串真的应该被认为是不可变的吗？

Consider the following code:

请考虑以下代码：

unsafe
{
    string foo = string.Copy("This can't change");

    fixed (char* ptr = foo)
    {
        char* pFoo = ptr;
        pFoo[8] = pFoo[9] = ' ';
    }

    Console.WriteLine(foo); // "This can   change"
}
unsaf