默认实现Object.GetHash code（） [英] Default implementation for Object.GetHashCode()

问题描述

如何为 GetHash code，其默认的实现（）工作？而且它处理结构，类，阵列等高效不够好？

我想，以决定在什么情况下，我要收拾我自己在什么情况下我可以放心地依赖于默认的实现做好。我不想重新发明轮子，如果在所有可能的。

解决方案

 命名空间系统{
    公共类对象{
        [MethodImpl（MethodImplOptions.InternalCall）
        内部静态外部INT InternalGetHash code（obj对象）;

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

InternalGetHash code 映射到 ObjectNative :: GetHash code 功能的CLR，这看起来是这样的：

  FCIMPL1（INT32，ObjectNative :: GetHash code，对象* OBJ）{
    CONTRACTL
    {
        抛出;
        禁用（GC_NOTRIGGER）;
        INJECT_FAULT（FCThrow（kOutOfMemoryException））;
        MODE_COOPERATIVE;
        SO_TOLERANT;
    }
    CONTRACTL_END;

    VALIDATEOBJECTREF（OBJ）;

    DWORD IDX = 0;

    如果（OBJ == 0）
        返回0;

    OBJECTREF坷Ref（OBJ）;

    HELPER_METHOD_FRAME_BEGIN_RET_1（坷Ref）; //设置一个框架

    IDX = GetHash codeEX（OBJECTREFToObject（坷Ref））;

    HELPER_METHOD_FRAME_END（）;

    返回IDX;
}
FCIMPLEND
 

全面实施 GetHash codeEX 是相当大的，所以它更容易只是链接到的 C ++源$ C ​​$ C 。

How does the default implementation for GetHashCode() work? And does it handle structures, classes, arrays, etc. efficiently and well enough?

I am trying to decide in what cases I should pack my own and in what cases I can safely rely on the default implementation to do well. I don't want to reinvent the wheel, if at all possible.

解决方案

namespace System {
    public class Object {
        [MethodImpl(MethodImplOptions.InternalCall)]
        internal static extern int InternalGetHashCode(object obj);

        public virtual int GetHashCode() {
            return InternalGetHashCode(this);
        }
    }
}

InternalGetHashCode is mapped to an ObjectNative::GetHashCode function in the CLR, which looks like this:

FCIMPL1(INT32, ObjectNative::GetHashCode, Object* obj) {  
    CONTRACTL  
    {  
        THROWS;  
        DISABLED(GC_NOTRIGGER);  
        INJECT_FAULT(FCThrow(kOutOfMemoryException););  
        MODE_COOPERATIVE;  
        SO_TOLERANT;  
    }  
    CONTRACTL_END;  

    VALIDATEOBJECTREF(obj);  

    DWORD idx = 0;  

    if (obj == 0)  
        return 0;  

    OBJECTREF objRef(obj);  

    HELPER_METHOD_FRAME_BEGIN_RET_1(objRef);        // Set up a frame  

    idx = GetHashCodeEx(OBJECTREFToObject(objRef));  

    HELPER_METHOD_FRAME_END();  

    return idx;  
}  
FCIMPLEND

The full implementation of GetHashCodeEx is fairly large, so it's easier to just link to the C++ source code.

这篇关于默认实现Object.GetHash code（）的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！