問(wèn)題描述

我已經(jīng)為 EventLogEntry 實(shí)現(xiàn)了一個(gè)自定義的 IEqualityComparer.

I've implemented a custom IEqualityComparer for EventLogEntry.

public class EventLogEntryListComparison :
    IEqualityComparer<List<EventLogEntry>>,
    IEqualityComparer<EventLogEntry>

對(duì)于IEqualityComparer>，GetHashCode函數(shù)很簡(jiǎn)單.

For IEqualityComparer<List<EventLogEntry>>, the GetHashCode function is very simple.

public int GetHashCode(List<EventLogEntry> obj)
{
    return obj.Sum(entry => 23 * GetHashCode(entry));
}

但是，對(duì)于某些條目，這會(huì)引發(fā) OverflowException.

However, this throws an OverflowException for certain entries.

"Arithmetic operation resulted in an overflow."
   at System.Linq.Enumerable.Sum(IEnumerable`1 source)
   at System.Linq.Enumerable.Sum[TSource](IEnumerable`1 source, Func`2 selector)
   at <snip>.Diagnostics.EventLogAnalysis.EventLogEntryListComparison.GetHashCode(List`1 obj) in C:dev<snip>Diagnostics.EventLogAnalysisEventLogEntryListComparison.cs:line 112
   at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
   at System.Collections.Generic.Dictionary`2.set_Item(TKey key, TValue value)
   at <snip>.Diagnostics.EventLogAnalysis.Program.AnalyseMachine(String validMachineName) in C:dev<snip>.Diagnostics.EventLogAnalysisProgram.cs:line 104
   at System.Threading.Tasks.Parallel.<>c__DisplayClass2d`2.<ForEachWorker>b__23(Int32 i)
   at System.Threading.Tasks.Parallel.<>c__DisplayClassf`1.<ForWorker>b__c()

在調(diào)試時(shí)嘗試得到相同的錯(cuò)誤并且無(wú)法在即時(shí)窗口中出現(xiàn)后，我將代碼更改為這個(gè)并再見(jiàn) OverflowException?

After trying to get the same error whilst debugging and couldn't in the immediate window, I changed the code to this and bye bye OverflowException?

int total = 0;
foreach (var eventLogEntry in obj)
{
    total += GetHashCode(eventLogEntry);
}

return total;

LINQ 的 Sum 函數(shù)有何不同?

How is it that LINQ's Sum function behaving differently?

編輯 2

感謝一些評(píng)論，更正和預(yù)期的 GetHashCode 函數(shù)現(xiàn)在如下，

Thanks to a few comments, the corrected and intended GetHashCode function is now as follows,

public int GetHashCode(List<EventLogEntry> obj)
{
    return unchecked(obj.Aggregate(17,
        (accumulate, entry) =>
        accumulate * 23 + GetHashCode(entry)));
}

推薦答案

LINQ 的 Enumerable.Sum(...) 方法在 checked 塊內(nèi)執(zhí)行加法.這意味著如果總和溢出，他們會(huì)故意拋出異常.

LINQ's Enumerable.Sum(...) methods perform the additions inside a checked block. This means that they deliberately throw an exception if the sum overflows.

您的 sum 不在 checked 塊內(nèi)，因此它是否引發(fā)異常取決于...是從 checked 塊內(nèi)調(diào)用它，還是我相信在程序集上的一個(gè)屬性.

Your sum is not inside a checked block, so whether or not it throws an exception depends on... whether it is called from inside a checked block, or a property on the assembly I believe.

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