How do I prepend every item in a list of strings in C# with a Lambda Expression

Question

I found a VB version of this here, but I'd like to use a Lambda Expression to take a List of strings and then prepend a string onto every item in the list.

It seems like using the ForEach ends up sending in the string by value, so any changes disappear. Here's the line of code I was hoping to have work.

listOfStrings.ForEach((listItem) => {listItem = listItem.Insert(0,"a");});

Answer 1

Strings are immutable, they cannot be altered "in place". Therefore, you'd have to replace each entry in the list which you cannot do with List<T>.ForEach. At this point you'd be best just making a new list:

listOfStrings = listOfStrings.Select(value => "a" + value).ToList();

Answer 2

If you need to modify the list in place, then an explicit for loop is appropriate.

for (int index = 0; index < list.Count; index++)
{
     list[index] = // modify away!
}

Otherwise, use the Select(Func<T, TOut> selector) with the optional .ToList() or .ToArray() as demonstrated by sixlettervariables.