Question

Ciao everyone,
i was finally able to switch from .NET Framework 2.0 to .NET Framework 4.0.

I am trying to get some experience about lambda expression and LINQ.

Is it possible to translate this:

for (int cont = 0;cont < args.Length; cont++)
    Console.WriteLine("#" + cont + " " + "<" + args + ">");

into a single line lambda expression,or using LINQ, or even some other costruct i am no aware of ?
Thank you in advance.

Answer 1

LINQ operations shouldn’t have side effects or do actions. They should only be used to produce, from a IEnumerable<T> another IEnumerable<T> (or from a IQueryable<T> another IQueryable<T> or IEnumerable<T>) (or if aggregating, like .Max, .All… a single result)

Read for example http://blogs.msdn.com/b/ericlippert/archive/2009/05/18/foreach-vs-foreach.aspx.

(and note that this question is quite asked on SO… Read for example my reply here ToList().ForEach in Linq and see a solution to a similar problem)

Now, if you hate yourself enough, you can do this:

strs.Select((p, index) =>
{
    Console.WriteLine("#" + index + " " + "<" + p + ">");
    return true;
}).All(p => p);

We are using the .All(p => p) to “materialize” the Select operation. This because Select is “lazy” and won’t be executed if no one cycles it.

Technically you could even try to obfuscate it a little:

strs.Select((p, index) =>
{
    Console.WriteLine("#" + index + " " + "<" + p + ">");
    return false;
}).Any(p => p);

(All checks that all the elements are true and stops if one of the is false, so it has to cycle all of them (because we always return true;). Any (as written) checks that at least one of the elements is true and then stops (but all of our elements are false, becasue we do return false; so the Any will cycle all the elements)

Now… The advantage of these techniques over using ToList is that we aren’t “duplicating” an Array to a List<T> just to use a “wrong” method of List<T>. If the ForEach method of List<T> is “wrong”, duplicating an Array to a List just to use it is doubly-wrong.