什么RuntimeHelpers.GetHash code执行 [英] What does RuntimeHelpers.GetHashCode do

问题描述

在 RuntimeHelpers.GetHash code（对象）方法允许基于对象的身份生成散列codeS。 MSDN 状态的：

  

在RuntimeHelpers.GetHash code方法总是调用   Object.GetHash code方法非实际上，即使对象的类型有   覆盖了Object.GetHash code方法。

  [MethodImpl（MethodImplOptions.InternalCall）
[SecuritySafeCritical]
公共静态外部INT GetHash code（对象o）;
 

然而，当检查使用反射（.NET 4.0）的 Object.GetHash code（）的方法，我们会看到下面的code：

 公共虚拟INT GetHash code（）
{
    返回RuntimeHelpers.GetHash code（本）;
}
 

这使我相信，MSDN文档是错误的，因为调用 Object.GetHash code 从在 RuntimeHelpers.GetHash code（对象）将导致堆栈溢出。

那么，什么是 RuntimeHelpers.GetHash code（对象）的实际行为，它是如何工作的？它是如何计算哈希？

解决方案

我觉得MSDN文档试图描述的的行为，而不是实现。关键点： RuntimeTypeHelpers 返回默认执行，你会得到均 object.GetHash code（）的没有的覆盖。

如果，例如，你想建立这确实是有用的引用相等的查找，即使对于那些已经覆盖等于和类型 GetHash code 。我这样做，我维持，采用了串行 RuntimeTypeHelpers.GetHash code（）和 Object.ReferenceEquals

The RuntimeHelpers.GetHashCode(object) method allows generating hash codes based on the identity of an object. MSDN states:

The RuntimeHelpers.GetHashCode method always calls the Object.GetHashCode method non-virtually, even if the object's type has overridden the Object.GetHashCode method.

[MethodImpl(MethodImplOptions.InternalCall)]
[SecuritySafeCritical]
public static extern int GetHashCode(object o);

However, when inspecting the Object.GetHashCode() method using Reflector (.NET 4.0), we'll see the following code:

public virtual int GetHashCode()
{
    return RuntimeHelpers.GetHashCode(this);
}

This makes me believe that the MSDN documentation is wrong, since calling Object.GetHashCode from within the RuntimeHelpers.GetHashCode(object) would cause a stack overflow.

So what is the actual behavior of RuntimeHelpers.GetHashCode(object) and how does it work? How does it calculate the hash?

解决方案

I think the MSDN documentation is trying to describe the behaviour, not the implementation. The key point: RuntimeTypeHelpers returns the default implementation that you would get were object.GetHashCode() not overridden.

This is really useful if, for example, you want to build a reference equality lookup, even for types that have overridden Equals and GetHashCode. I do this in a serializer that I maintain, using RuntimeTypeHelpers.GetHashCode() and Object.ReferenceEquals.

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