GetHashCode issue for ValueObjects with two equality components of the same type.

Hi,

I've been helping teach programmers the benefits of ValueObjects; the example we were using led us to create ValueObjects for the 2-dimensional cartesian coordinate system with only integers as positions.

public sealed class Position : ValueObject
{
     public int X {get;}
     public int Y {get;}
}

Where X and Y would be the EqualityComponents.

There is an issue with the GetHashCode method since the exclusive OR would give the same HashCode for (1,1), and (2,2) (in fact, any point where X = Y). That HashCode would be 0. This issue only affects ValueObjects with at least two equality components of the same type; as their hashcodes could cancel each other.

I corrected this issue by using the following method, is it a viable fix? And should this fix be applied to all future ValueObjects?

public override int GetHashCode()
{
    return GetEqualityComponents()
                   .Select(x => x != null ? x.GetHashCode() : 0)
                   .Aggregate((x, y) => HashCode.Combine(x,y));
}

Regards, Adam

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ID: 70b14bbb-dc66-f1a2-8b14-39ef3b4bde1d
Version Independent ID: cf912666-9ad3-1673-8f69-6bf52c034ef9
Content: Implementing value objects
Content Source: docs/architecture/microservices/microservice-ddd-cqrs-patterns/implement-value-objects.md
Product: dotnet-architecture
Technology: microservices
GitHub Login: @nishanil
Microsoft Alias: nanil

dotnet / docs

GetHashCode issue for ValueObjects with two equality components of the same type. #29690

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