Generators in C#?

Question

In javascript I can create a generator which would behave like this:

function* idMaker(){
  var index = 0;
  while(true)
    yield index++;
}

var gen = idMaker();

console.log(gen.next().value); // 0
console.log(gen.next().value); // 1
console.log(gen.next().value); // 2

What would the C# equivalent look like?

I wonder whether this will work:

static System.Collections.Generic.IEnumerable<int> MakeId()
{
  int index = 0;
  while (true)
    yield return index++;
}

but from what I understand of C# so far, the above wouldn't work as I intend and instead infinite loop.

Answer 1

You can do the same with your MakeId in the following way:

using (var gen = MakeId().GetEnumerator()) {
    gen.MoveNext();
    Console.WriteLine(gen.Current); // 0
    gen.MoveNext();
    Console.WriteLine(gen.Current); // 1
    gen.MoveNext();
    Console.WriteLine(gen.Current); // 2
}

If you don't like to call MoveNext all the time, you can write extension method:

public static class Extensions {
    public static T NextValue<T>(this IEnumerator<T> enumerator) {
        enumerator.MoveNext();
        return enumerator.Current;
    }
}

Then it becomes

using (var gen = MakeId().GetEnumerator()) {                
    Console.WriteLine(gen.NextValue()); // 0                
    Console.WriteLine(gen.NextValue()); // 1                
    Console.WriteLine(gen.NextValue()); // 2
}

Answer 2

Well, the C# equivalent to your code is:

static void Main()
{
    var enumerator = MakeId().GetEnumerator();

    enumerator.MoveNext();
    Console.WriteLine(enumerator.Current); // 0    
    enumerator.MoveNext();
    Console.WriteLine(enumerator.Current); // 1    
    enumerator.MoveNext();
    Console.WriteLine(enumerator.Current); // 2

}

static IEnumerable<int> MakeId()
{
  int index = 0;
  while (true)
    yield return index++;
}

GetEnumerator returns an enumerator that iterates through a collection.