Answer by Dor Rotman for LINQ equivalent of foreach for IEnumerable

I took Fredrik's method and modified the return type.

This way, the method supports deferred execution like other LINQ methods.

EDIT: If this wasn't clear, any usage of this method must end with ToList() or any other way to force the method to work on the complete enumerable. Otherwise, the action would not be performed!

public static IEnumerable<T> ForEach<T>(this IEnumerable<T> enumeration, Action<T> action)
{
    foreach (T item in enumeration)
    {
        action(item);
        yield return item;
    }
}

And here's the test to help see it:

[Test]
public void TestDefferedExecutionOfIEnumerableForEach()
{
    IEnumerable<char> enumerable = new[] {'a', 'b', 'c'};

    var sb = new StringBuilder();

    enumerable
        .ForEach(c => sb.Append("1"))
        .ForEach(c => sb.Append("2"))
        .ToList();

    Assert.That(sb.ToString(), Is.EqualTo("121212"));
}

If you remove the ToList() in the end, you will see the test failing since the StringBuilder contains an empty string. This is because no method forced the ForEach to enumerate.