Using Array.Foreach to modify the collection

Question

I want to remove spaces from the beginning and end of the string (Trim) in all positions of array, but none of the ways below worked.
What am I doing wrong?

var optionArray = new string[] { "in the jungle ", " the mighty jungle", " the lion sleeps tonight " };

Array.ForEach(optionArray, x => x.Trim()); // nada acontece
Array.ForEach(optionArray, x => x = x.Trim()); // nada acontece
optionArray = Array.ForEach(optionArray, x => x = x.Trim()); // Cannot implicitly convert type 'void' to 'string[]'

var optionList = optionArray.ToList();

optionList.ForEach(x => x.Trim()); // nada acontece
optionList.ForEach(x => x = x.Trim()); // nada acontece
optionList = optionList.ForEach(x => x = x.Trim()); // Cannot implicitly convert type 'void' to 'System.Collections.Generic.List<string>'

Answer 1

Daniel complementing Maniero’s response, the Eric Lippert in 2009 he wrote a good article in his blog, in it it explains the evils of using the List<T>.ForEach in place of foreach. You can read the article in full at the following link.: "foreach" vs "foreach"

Another argument would be that Micrsoft’s own architects decided not to include a method ForEach at Linq, you can read about the subject at.: Why no Foreach method on Ienumerable interfaces

but in short, you should not use the List<T>.ForEach, why it violates the principles of functional programming and may cause some side effects. besides, the List<T>.ForEach is less readable and this may imply a more difficult maintenance (try debug an iteration within a List<T>.ForEach).

Still, this is a scenario where this kind of implementation can be useful, parallelism... and yet there is a whole Namespace for this purpose: https://msdn.microsoft.com/en-us/library/system.threading.tasks.parallel(v=vs.110). aspx

var lista = Enumerable.Range(1, 10).ToList();
Parallel.ForEach(lista, (item, state, indice) => {
    Console.WriteLine(string.Format("indice: {0}, value: {1}", indice, item));
});

but the implementation will still suffer from the same problem, you will not be able to modify the list, in this case you need to make use of the Parallel.For and access the element by the index.:

var lista = Enumerable.Range(1, 10).ToList();
Parallel.For(0, lista.Count, (indice, state) => {
    lista[indice] *= 2;
});

foreach(var item in lista) {
    Console.WriteLine(string.Format("value: {0}", item));
}

I put in the Github for future reference.

And finally, a good reason not to use the .Select(s => s.Trim()).ToArray(), you are not modifying the values of array. You are creating a new array with the new values, at this point you will have two arrays in memory, then will be just wasting memory, CPU cycles and forced that the Garbage Collector be called more often.

Answer 2

You can use the Select() from LINQ, but need to create a new array:

var newArray = optionArray.Select(s => s.Trim()).ToArray();

Unless you want to do "manual" (probably what I would do):

for (var i = 0; i < optionArray.Length; i++) {
    optionArray[i] = optionArray[i].Trim();
}

Behold working in the ideone. And in the .NET Fiddle. Also put on the Github for future reference.