Usage of hash code causes comparison to return wrong result

It seems like the code uses hash codes to prevent cycles during the comparison of objects. The hash code is used as a key for a dictionary. I think this is not a good idea because hash codes do not have to be unique. It is absolutely valid for two different objects to have the same hash code. We actually have exactly a situation where comparison fails for this reason.

Here is some example code which should show the problem (the test fails)

[TestClass]
public class TestHashCode
{
    [TestMethod]
    public void Test_SameHashCode()
    {
        Details details1 = new Details { fooType = new FooType { typeId = 1 }, additionalInfo = "info" };
        Details details2 = new Details { fooType = new FooType { typeId = 2 }, additionalInfo = "info" };

        CompareLogic logic = new CompareLogic();
        ComparisonResult cmpResult = logic.Compare(details1, details2);

        Assert.IsFalse(cmpResult.AreEqual);
    }
}

public class FooType
{
    public int typeId;

    public override int GetHashCode()
    {
        return typeId;
    }

    public override bool Equals(object obj)
    {
        FooType other = obj as FooType;
        if (other == null)
            return false;

        return this.typeId == other.typeId;
    }
}

public class Details
{
    public FooType fooType;
    public string additionalInfo;

    public override int GetHashCode()
    {
        return this.fooType.GetHashCode();
    }

    public override bool Equals(object obj)
    {
        Details other = obj as Details;
        if (other == null)
            return false;

        if (this.fooType.Equals(other.fooType) == false)
            return false;

       return this.additionalInfo.Equals(other.additionalInfo);
    }
}

[GregFinzer]

No thank you.

[sbradl]

Don’t you even want to give a reason why you won’t fix it?