Olema Olema - 1 year ago 91
C# Question

Why is .ForEach() on IList<T> and not on IEnumerable<T>?

Possible Duplicate:

Why is there not a ForEach extension method on the IEnumerable interface?

I've noticed when writing LINQ-y code that .ForEach() is a nice idiom to use. For example, here is a piece of code that takes the following inputs, and produces these outputs:

{ "One" } => "One"
{ "One", "Two" } => "One, Two"
{ "One", "Two", "Three", "Four" } => "One, Two, Three and Four";

And the code:

private string InsertCommasAttempt(IEnumerable<string> words)
List<string> wordList = words.ToList();
StringBuilder sb = new StringBuilder();
var wordsAndSeparators = wordList.Select((string word, int pos) =>
if (pos == 0) return new { Word = word, Leading = string.Empty };
if (pos == wordList.Count - 1) return new { Word = word, Leading = " and " };
return new { Word = word, Leading = ", " };

wordsAndSeparators.ToList().ForEach(v => sb.Append(v.Leading).Append(v.Word));
return sb.ToString();

Note the interjected .ToList() before the .ForEach() on the second to last line.

Why is it that .ForEach() isn't available as an extension method on IEnumerable? With an example like this, it just seems weird.

Thanks in advance,


Answer Source

Because ForEach(Action) existed before IEnumerable<T> existed.

Since it was not added with the other extension methods, one can assume that the C# designers felt it was a bad design and prefer the foreach construct.


If you want you can create your own extension method, it won't override the one for a List<T> but it will work for any other class which implements IEnumerable<T>.

public static class IEnumerableExtensions
  public static void ForEach<T>(this IEnumerable<T> source, Action<T> action)
    foreach (T item in source)
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