Don't understand why the ForEach command isn't working

Question

I am wanting to trim any white space off a collection of strings. I used the following code but it doesn't seem to work. Could anyone explain why?

result.ForEach(f => f = f.Trim());

Answer 1

This won't work because you are assigning a new string reference to a local variable. This is probably what you are looking for:

result = result.Select(f => f.Trim()).ToList();

Answer 2

You are re-assigning the argument variable inside the scope of the lambda. It's a collapsed form of:

foreach(string value in myList)
{
    Lambda(value);
}

void Lambda(string input)
{
    input = input.Trim();
}

The simplest way would probably be to use a projection:

myList = myList.Select(str => str.Trim()).ToList();

Answer 3

foreach doesn't give you write access to the underlying collection, it only iterates through it, which means your change isn't stored back into the collection.

You can do two things:

1. Produce a new collection

   var newResult = result.Select(f => f.Trim()).ToList();
   

2. Use a normal for-loop and change the original collection

   for (int index = 0; index < result.Count; index++)
       result[index] = result[index].Trim();