CODEWITHSUNDEEP
c#dictionarykey
user1935724
user1935724

Reputation: 554

ContainsKey return unexpected result C# this is super strange needs advice

I have a

Dictionary<NodePair, string> repo;

I have implemented the 

GetHashCode(), Equals()

on the 

NodePair

When I try to search for a key using 

if(Repo.ContainsKey(new NodePair(OneTree.Root, AnotherTree.Root)))

it return false, however, when I do

foreach (NodePair pair in Repo.Keys)
   if (pair.Equals(new NodePair(OneTree.Root, AnotherTree.Root)))
        Console.WriteLine();

The debugger stops at the 

Console.WriteLine()

same thing happened when I do 

foreach (NodePair pair in Repo.Keys)
   if (pair.GetHashCode() == (new NodePair(OneTree.Root, AnotherTree.Root)).GetHashCode())
        Console.WriteLine();

So why the hack that ContainsKey() return false?????????

Edit put everything together:

 foreach (NodePair pair in Repo.Keys)
    if (pair.Equals(new NodePair(OneTree.Root, AnotherTree.Root)))
         Console.WriteLine();

 foreach (NodePair pair in Repo.Keys)
    if (pair.GetHashCode() == (new NodePair(OneTree.Root, AnotherTree.Root)).GetHashCode())
         Console.WriteLine();

 if (Repo.ContainsKey(new NodePair(OneTree.Root, AnotherTree.Root)))
      Console.WriteLine();

The first two Console.WriteLine() hit and last one did not. Anyone can explain?

Upvotes: 0

Views: 60

Answers (1)

CodingYoshi
CodingYoshi

Reputation: 26989

It is implemented like:

private int FindEntry(TKey key)
{
    if (key == null)
    {
        ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key);
    }

    if (buckets != null)
    {
        int hashCode = comparer.GetHashCode(key) & 0x7FFFFFFF;
        for (int i = buckets[hashCode % buckets.Length]; i >= 0; i = entries[i].next)
        {
            if (entries[i].hashCode == hashCode && comparer.Equals(entries[i].key, key)) return i;
        }
    }
    return -1;
}

You can see the full source code for Dictionary if you want because it is available online. If you want to debug it, please see how to debug .NET code.

Upvotes: 2

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