One wonders why C# can’t supply the second GetEnumerator() function automatically.

Is it possible for you to post a minimal example showing the error. Similar to the Ints example in the post?

For example, here is a generic repeater class. That is, when you construct the class you give it an element to repeat and how many times it should be repeated.

using System;
using System.Collections.Generic;

class Repeater<T> : IEnumerable<T> {
  private readonly T elem;
  private readonly int no_of_times;
  public Repeater(int no, T e) { no_of_times = no; elem = e; }
  public IEnumerator<T> GetEnumerator() {
    for(int i = 0; i < no_of_times; ++i)
      yield return elem;
  }
  System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
    return GetEnumerator();
  }
}

class MainClass {
  public static void Main(string[] args) {
     Repeater<string> hellos = new Repeater<string>(10, "Hello");
     foreach (string s in hellos)
        Console.WriteLine(s);
  }
}