Use byte[] as key in dictionary

Question

I need to use a byte[] as a key in a Dictionary. Since byte[] doesn\'t override the default GetHashCode method, two sepa

Answer 1

Just made the EqualityComparer a little more generic, by not working on arrays but on IEnumerable<T>.

Due to the fact, that we now have a T we need to be able to specify an optional equality comparer for the elements.

Last but not least, GetHashCode() should never throw and sometimes you need it fast and sometimes you need it more accurate in the first run. So you can optionally define an accuracy from how many items (maximum) the hash code should be taken into account for our own hash.

public class EnumerableEqualityComparer<T> : IEqualityComparer<IEnumerable<T>>
{
    private static readonly Lazy<IEqualityComparer<IEnumerable<T>>> Lazy = new Lazy<IEqualityComparer<IEnumerable<T>>>(() => new EnumerableEqualityComparer<T>());
    private int accuracy;
    private IEqualityComparer<T> comparer;

    public EnumerableEqualityComparer()
        : this(-1)
    {
    }

    public EnumerableEqualityComparer(int accuracy)
        : this(accuracy, null)
    {
    }

    public EnumerableEqualityComparer(IEqualityComparer<T> elementEqualityComparer)
        : this(-1, elementEqualityComparer)
    {
    }

    public EnumerableEqualityComparer(int accuracy, IEqualityComparer<T> elementEqualityComparer)
    {
        if (accuracy < 0)
        {
            accuracy = 4;
        }

        this.accuracy = accuracy;
        comparer = elementEqualityComparer ?? EqualityComparer<T>.Default;
    }

    public static IEqualityComparer<IEnumerable<T>> Default { get; private set; } = Lazy.Value;

    public bool Equals(IEnumerable<T> x, IEnumerable<T> y)
    {
        if (ReferenceEquals(x, y))
        {
            return true;
        }

        if (ReferenceEquals(x, null)
            || ReferenceEquals(y, null))
        {
            return false;
        }

        return x.SequenceEqual(y, comparer);
    }

    public int GetHashCode(IEnumerable<T> obj)
    {
        if (ReferenceEquals(obj, null))
        {
            return -1;
        }

        var count = (obj as ICollection<T>)?.Count ?? 1;
        var hashCode = count * 49297;

        foreach (var item in obj.Take(accuracy))
        {
            hashCode += comparer.GetHashCode(item) * 17123;
        }

        return hashCode;
    }
}