Is the .NET foreach statement guaranteed to iterate a collection in the same order in which it was built?

Question

A coworker used a for loop to iterate a List in some C# code he wrote and left the comment, "did't use For Each because I wasn't sure it iterates in order. Who knows what Microsoft will do." For example, suppose we have a List built up like this:

var someList = new List<string>();

someList.Add("one");
someList.Add("two");
someList.Add("three");

my coworker used something like this:

for (int i = 0; i < someList.Count; i++)    
{
    System.Diagnostics.Debug.WriteLine(someList[i]);
}

instead of this:

foreach (var item in someList)              
{
    System.Diagnostics.Debug.WriteLine(item);
}

I guess he's afraid the items might come out in a different order than they were added to the collection. I think he's being a bit paranoid, but technically, the documentation does not state the order in which the collection is iterated. Is it possible for a foreach statement to traverse an array or collection object in any order other than from lowest bound to highest?

Answer 1

Your question is regarding a List<T>, which does maintain order.

foreach, alone, is not guaranteed to do anything. It just asks the object provided for its enumerator, which could do anything, potentially.