Lambda Expression using Foreach Clause...

Question

EDIT

For reference, here's the blog post which eric referrrred to in the comments

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

ORIG

More of a curiosity I suppose but one for the C# Specification Savants...

Why is it that the ForEach() clause doesn't work (or isn't available) for use on IQueryable/IEnumerable result sets...

You have to first convert your results ToList() or ToArray() Presumably theres a technical limitation to the way C# iterates IEnumerables Vs. Lists... Is it something to do with the Deferred Execution's of IEnumerables/IQuerable Collections. e.g.

var userAgentStrings = uasdc.UserAgentStrings
    .Where<UserAgentString>(p => p.DeviceID == 0 && 
                            !p.UserAgentString1.Contains("msie"));
//WORKS            
userAgentStrings.ToList().ForEach(uas => ProcessUserAgentString(uas));         

//WORKS
Array.ForEach(userAgentStrings.ToArray(), uas => ProcessUserAgentString(uas));

//Doesn't WORK
userAgentStrings.ForEach(uas => ProcessUserAgentString(uas));

Answer 1

It's perfectly possible to write a ForEach extension method for IEnumerable<T>.

I'm not really sure why it isn't included as a built-in extension method:

• Maybe because ForEach already existed on List<T> and Array prior to LINQ.
• Maybe because it's easy enough to use a foreach loop to iterate the sequence.
• Maybe because it wasn't felt to be functional/LINQy enough.
• Maybe because it isn't chainable. (It's easy enough to make a chainable version that yields each item after performing an action, but that behaviour isn't particularly intuitive.)

---

public static void ForEach<T>(this IEnumerable<T> source, Action<T> action)
{
    if (source == null) throw new ArgumentNullException("source");
    if (action == null) throw new ArgumentNullException("action");

    foreach (T item in source)
    {
        action(item);
    }
}

Answer 2

What an amazing coincidence, I just now wrote a blog article about this very question. It will be was published May 18th. There is no technical reason why we (or you!) couldn't do this. The reasons why not are philosophical. See my blog next week for my argument.