C# reflection-based object diff

obj-diff.cs

public class Compared
{
    public object Left { get; set; }
    public object Right { get; set; }
}

public static System.Collections.Generic.Dictionary<string, Compared> Diff(object o1, object o2)
{
    var result = new System.Collections.Generic.Dictionary<string, Compared>(StringComparer.Ordinal);

    if (o1.GetType() != o2.GetType())
    {
        throw new ArgumentException("Objects are not of the same type");
    }

    var oType = o1.GetType();

    foreach (System.Reflection.PropertyInfo prop in oType.GetProperties())
    {
        object o1Value = prop.GetValue(o1);
        object o2Value = prop.GetValue(o2);

#warning This only supports collections of primitives, not collections of collections. Fine for our purposes but not general purpose without further work.

        if (prop.PropertyType != typeof(string) && typeof(System.Collections.IEnumerable).IsAssignableFrom(prop.PropertyType))
        {
            var seq1 = (System.Collections.IEnumerable)o1Value;
            var seq2 = (System.Collections.IEnumerable)o2Value;

            int cnt1 = seq1.Cast<object>().Count();
            int cnt2 = seq2.Cast<object>().Count();

            if (cnt1 != cnt2)
            {
                result.Add(prop.Name, new Compared { Left = $"{cnt1} items", Right = $"{cnt2} items" });
            }

            var enumerator1 = seq1.GetEnumerator();
            var enumerator2 = seq2.GetEnumerator();

            for (int i = 0; i < cnt1; i++)
            {
                enumerator1.MoveNext();
                enumerator2.MoveNext();

                var o1eValue = enumerator1.Current;
                var o2eValue = enumerator2.Current;

                if (!object.Equals(o1eValue, o2eValue))
                {
                    result.Add(prop.Name, new Compared { Left = $"item {i}={o1eValue}", Right = $"item {i}={o2eValue}" });
                }
            }
        }
        else
        {
            if (!object.Equals(o1Value, o2Value))
            {
                result.Add(prop.Name, new Compared { Left = o1Value, Right = o2Value });
            }
        }
    }

    return result;
}