using System.Collections;
using System.Collections.Generic;

namespace InferenceBug
{
    public class MyDictionary: IEnumerable<int>, IEnumerable<KeyValuePair<string, int>>
    {
        public MyDictionary()
        {
            _source = new Dictionary<string, int>();
        }

        private readonly IDictionary<string, int> _source;

        IEnumerator<KeyValuePair<string, int>> IEnumerable<KeyValuePair<string, int>>.GetEnumerator()
        {
            return _source.GetEnumerator();
        }

        IEnumerator<int> IEnumerable<int>.GetEnumerator()
        {
            return _source.Values.GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return _source.GetEnumerator();
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            // one implementation of IEnumerable: works fine
            Test(new Dictionary<string, int>
            {
                ["A"] = 1,
                ["B"] = 2
            });

            // two implementations: fails
            Test(new MyDictionary());
        }

        private static void Test<T>(IEnumerable<KeyValuePair<string, T>> arg)
        {
            // does nothing
        }
    }
}