by Paulo Morgado via Paulo Morgado : C# on 5/14/2007 10:28:19 PM
Looks like I was way wrong in here and here.
I had thought that from the top of my head because I tried to use Array.IndexOf as an extension method and was surprised to see that it wasn't an extension method.
It presented a good opportunity to play around with extension methods, so I wrote a class to extend the Array class:
public static class ArrayUtils
{
public static int IndexOf<T>(this T[] array, T value)
return System.Array.IndexOf(array, value);
}
public static int IndexOf<T>(this T[] array, T value, int startIndex)
return System.Array.IndexOf(array, value, startIndex);
public static int IndexOf<T>(this T[] array, T value, int startIndex, int count)
return System.Array.IndexOf(array, value, startIndex, count);
It was so easy that I thought: "Why dind't they do it?".
While I was trying to write a proof of concept around making such a change in a class (changing normal static methods into extension methods). It was as simple as adding a this keyword:
public class MyClass
private int myField;
public int MyProperty
get { return myField; }
set { myField = value; }
public static bool IsNullOrEmpty(this MyClass value)
if (value == null) return true;
if (value.myField == 0) return true;
return false;
The output of the compiler just chilled my enthusiasm:
MyCsClass.cs(18,47): error CS1106: Extension methods must be defined in a non generic static class
What is this all about? How had I missed it in here and here?
Here's how I had missed it:
http://search.msdn.microsoft.com/search/Default.aspx?brand=msdn&query=%22non-nested%22+%22non-generic%22+%22static+class%22+%22extension+methods%22
http://search.live.com/results.aspx?q=%22non-nested%22+%22non-generic%22+%22static+class%22+%22extension+methods%22
I should have tried this:
http://www.google.com/custom?client=pub-3578125481836759&channel=1972798655&cof=S%3Ahttp%3A%2F%2Fsearchdotnet.com%2Fdefault.aspx%3BCX%3ADotNet%2520Developers%2520Search%2520Engine%3BL%3Ahttp%3A%2F%2Fwww.searchdotnet.com%2Fimages%2Fsearchnet.jpg%3BLH%3A36%3BLP%3A1%3B&q=%22non-nested%22+%22non-generic%22+%22static+class%22+%22extension+methods%22
THIS is the most recent (I think) specification of C# 3.0 and it states that:
Extension methods are declared by specifying the keyword this as a modifier on the first parameter of the methods. Extension methods can only be declared in non-generic, non-nested static classes.
Now it's all clear!
Original Post: UPDATE: Extension methods
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