Extension methods in .NET 3.5 – cool stuff!!

One of the new features in .NET 3.5 are extension methods. These are a way you can sort of "tack on" some additional methods for a data type, without modifying or inheriting from the actual data type. ScottGu talked about it over here: http://weblogs.asp.net/scottgu/archive/2007/03/13/new-orcas-language-feature-extension-methods.aspx

So one of the things I was thinking – was how to best use this? It has some definite pros and cons. The pros should be obvious – one can keep the .NET run-time and developed components much simpler, because you don’t need to inherit from a class to make slight enhancements to it. One of the cons would be that this can end up making intellisense difficult to use because of too MUCH functionality.

For example, I was thinking "what extensions would I add to System.String?". The first thing that came to mind was – every single .Parse and .TryParse that I use all the time. Using extension methods, I could make it slightly easier to deal with converting a string into an int, DateTime, Uri, etc. So, let’s start with this. Below is a class that applies extension methods to System.String:

Download: StringExtensions.cs

So this is how this changes System.String:



So again, I am on the fence whether this is better, worse or just a wash. For example, in code, here is what this did for us:

    string testString = "14";

    long theCount = -1;


    if (long.TryParse(testString, out theCount))



        MessageBox.Show("Couldn’t parse");

And with the extension method, here’s how this translates:

    string testString = "14";

    long theCount = -1;


    if (testString.TryParseAsLong(out theCount))



        MessageBox.Show("Couldn’t parse");

I like the idea of this functionality being pushed back to the type, so that the code appears to stay with the string (versus getting "long" involved) – but I wonder if the fact that isn’t consistent, makes it not worth doing. If I had 1 huge project or a developer framework – I might add this perhaps – but I suppose .NET 3.5 will need to age a little bit to see where extension methods end up being most useful!

Posted in .NET 3.5, Uncategorized

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