Question

In C#, is there an IEqualityComparer<IEnumerable> that uses the SequenceEqual method to determine equality?

Answer 1

There is no such comparer in .NET Framework, but you can create one:

public class IEnumerableComparer<T> : IEqualityComparer<IEnumerable<T>>
{
    public bool Equals(IEnumerable<T> x, IEnumerable<T> y)
    {
        return Object.ReferenceEquals(x, y) || (x != null && y != null && x.SequenceEqual(y));
    }

    public int GetHashCode(IEnumerable<T> obj)
    {
        // Will not throw an OverflowException
        unchecked
        {
            return obj.Where(e => e != null).Select(e => e.GetHashCode()).Aggregate(17, (a, b) => 23 * a + b);
        }
    }
}

In the above code, I iterate over all items of the collection in the GetHashCode. I don’t know if it’s the wisest solution but this what is done in the internal HashSetEqualityComparer.