Question

I have a class with two properties, say

public class Book {
public string TitleSource { get; set; }
public string TitleTarget { get; set; }
}

I have an IList<Book> where the TitleTarget is null and for each item in the list, I need to copy the TitleSource property to the TitleTarget property. I could do this through a loop, sure, but it seems like there’s a LINQ or nice declarative way to do this. Is there?

Answer 1

Linq was designed as a way to consume things. If you look at web discussions about why there is no IEnumerable.ForEach(…) extension, you’ll see that the Linq designers purposefully avoided Linq to Object scenarios where the methods were designed to change object values.

That said, you can cheat by “selecting” values and not using the results. But, that creates items which are thrown away. So, a foreach loop is much more efficient.

Edit for people who really want something besides foreach

Another “cheat” that wouldn’t produce a new list would be to use a method that does little work of it’s own, like Aggregate, All, or Any.

// Return true so All will go through the whole list.
books.All(book => { book.TitleTarget = book.TitleSource; return true; });