CODEWITHSUNDEEP
c#.net
Maximus
Maximus

Reputation: 1299

C# equality with list-based properties

I've read numerous articles related to proper equality in C#:

http://www.loganfranken.com/blog/687/overriding-equals-in-c-part-1/

What is the best algorithm for an overridden System.Object.GetHashCode?

Assume the following sample class:

public class CustomData
{
    public string Name { get; set;}

    public IList<double> Values = new List<double>();
}

Would it still be the case to compare the Values property using .Equals()? Here is a full equality sample of what I mean:

#region Equality

    public override bool Equals(object value)
    {
        if(Object.ReferenceEquals(null, value)) return false;   // Is null?
        if (Object.ReferenceEquals(this, value)) return true;   // Is the same object?
        if (value.GetType() != this.GetType()) return false;    // Is the same type?

        return IsEqual((CustomData)value);
    }

    public bool Equals(CustomData obj)
    {
        if (Object.ReferenceEquals(null, obj)) return false;    // Is null?
        if (Object.ReferenceEquals(this, obj)) return true;     // Is the same object?

        return IsEqual(obj);
    }

    private bool IsEqual(CustomData obj)
    {
        return obj is CustomData other
            && other.Name.Equals(Name)
            && other.Values.Equals(Values);
    }

    public override int GetHashCode()
    {
        unchecked
        {
            // Choose large primes to avoid hashing collisions
            const int HashingBase = (int) 2166136261;
            const int HashingMultiplier = 16777619;

            int hash = HashingBase;
            hash = (hash * HashingMultiplier) ^ (!Object.ReferenceEquals(null, Name) ? Name.GetHashCode() : 0);
            hash = (hash * HashingMultiplier) ^ (!Object.ReferenceEquals(null, Values) ? Values.GetHashCode() : 0);
            return hash;
        }
    }

    public static bool operator ==(CustomData obj, CustomData other)
    {
        if (Object.ReferenceEquals(obj, other)) return true;
        if (Object.ReferenceEquals(null, obj)) return false;    // Ensure that "obj" isn't null

        return (obj.Equals(other));
    }

    public static bool operator !=(CustomData obj, CustomData other) => !(obj == other);

#endregion

Upvotes: 5

Views: 920

Answers (1)

user8061994
user8061994

Reputation:

List<T>.Equals(List<T> other) will compare references. If you want equality for property Values to be defined as identical sequences of doubles, use the IEnumerable<TSource>.SequenceEqual.(IEnemerable<TSource> other) method (MSDN). See a refactored version of your IsEqual(CustomData obj) below:

private bool IsEqual(CustomData obj)
{
    return obj is CustomData other
        && other.Name.Equals(Name)
        && other.Values.SequenceEqual(Values);
}

Upvotes: 3

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