As astute colleague noticed something funny in my recent post. Specifically, this piece of code:

postsWithCount.AsEnumerable().Select(pd => Rebuild(pd));

private void Rebuild(PostData postData)
{
    Post post = postData.Post;
    post.User = postData.User;
    post.Comments.Attach(postData.Comments);
}

What on earth am I doing here? Maybe it will help if I write the same code in a different way:

foreach (var postData in postsWithCount)
{
    Rebuild(postData);
}

private void Rebuild(PostData postData)
{
    Post post = postData.Post;
    post.User = postData.User;
    post.Comments.Attach(postData.Comments);
}

Yup, I'm quite naughtily using Select as a ForEach. I've been experimenting with this for a while now and the outcome is clear - it makes your code confusing.

Sadly, there is a ForEach<> method on System.Array but no extension method for IEnumerable<> :(

UPDATE: There are two humdingers in this post that people correctly noted in comments and e-mail to me:

• The Select() extension method is delayed and, in the example above would likely never get executed. This is a good lesson in testing code before you post it to your blog. The example was cut & paste together from subtly different code where this wouldn't have happened and that led to these mistakes. Oops.
• This example wouldn't even compile - the Select() extension expression must return something but my Rebuild is void so this would have resulted in a compiler error. Oops again.

These are embarassing mistakes to make and I was tempted to just delete the post, but that would seem dishonest somehow, so I'll leave it here with this note.