The Unity3D StartCoroutine calls a function, when does that function return?

Question

I know that Unity3D StartCoroutine calls a function which runs on the same thread as StartCoroutine, but when does the called function return back to the original caller?

Answer 1

I looked around the internet for a good Unity3D Coroutine example and couldn't find a complete one. There is a great explanation by UnityGems, but even their example is incomplete. So I wrote my own example.

This:

using UnityEngine;
using System.Collections;
public class MainCamera: MonoBehaviour {
  void Start () {
    Debug.Log ("About to StartCoroutine");
    StartCoroutine(TestCoroutine());
    Debug.Log ("Back from StartCoroutine");
  }
  IEnumerator TestCoroutine(){
    Debug.Log ("about to yield return WaitForSeconds(1)");
    yield return new WaitForSeconds(1);
    Debug.Log ("Just waited 1 second");
    yield return new WaitForSeconds(1);
    Debug.Log ("Just waited another second");
    yield break;
    Debug.Log ("You'll never see this"); // produces a dead code warning
  }
}

Produces this output:

About to StartCoroutine
about to yield return WaitForSeconds(1)
Back from StartCoroutine
Just waited 1 second
Just waited another second