For the unenlightened, extension methods are a new feature of the .NET 3.5 framework that allows you to extend any class — whether it is a built-in class, a third-party class, or your own class.

When you create an extension method, you can call the new method as if it were a native method of the class.

As an easy-to-understand example, I created an extension of the .NET String class called SuperTrim().  The method works like the built-in Trim() method, but instead of just trimming spaces from the front and back of a string, it trims any kind of control characters (any character with an ASCII code of less than 32, plus a few others).

After creating the extension method, I can apply SuperTrim() to an string in exactly the same way I would apply a regular Trim():

newString = oldString.SuperTrim()

Now that's cool! 

Last week I came upon a scenario in a program where I had to manipulate all of the items in a collection, so I tried using the built-in ForEach() method.  The trouble is that ForEach() is designed to do something with all the items in a collection, but not to change all of the items in a collection.

ForEach() passes each item, one by one, to your specified function, but it explicitly only passes the item by value, not by reference.  If your function changes the value passed, it is not changed in the collection — only within the scope of your function.

ForEach() also does not pass an index number or any other value that could help determine which item in the collection to change, so any attempt to use ForEach() to change items in the original collection would be a messy affair.

In response, I created an extension to iCollection called ChangeAll().  You pass a function to ChangeAll() that will receive each item, one by one, and the return value from your function will become the new value of that item in the collection.

Incidentally, ChangeAll() works great with the new lambda expressions — another won....

[ More ]