Reserving Judgment

I have been very quick to put down certain pieces of the .NET 3.5 framework (reference prior post on extension methods and partial methods), most specifically extension methods and partial methods. I'm not quite ready to give in on partial methods yet, they still just seem like a tool used to make code generators slightly easier, but I think I'm ready to reserve judgment on extension methods now.

I still think extension methods are dangerous and are going to be subject to blatant misuse. That being said, I think I need to keep an open mind regarding the potential uses for extension methods. Note that I'm referring to the use of extension methods entirely within code that you control.

I recently read a blog post by Greg Young titled A Use For Extension Methods where he basically stated that there are a lot of people out there that share my kind of viewpoint. He also wanted to show one possible way where extension methods could be used. He basically showed that extension methods were useful in controlling the context of intellisense when using a fluent interface for a pseudo-builder pattern. I call it pseudo since really there is only one type of available builder.

Basically his extension method looks like the following:

           
              
public class Builder
                
{
                
}
                
 
            
             
public class Create
              
{
              
    public static Builder New = new Builder();
              
}
          
            
public static CostBuilder Cost(this Builder s)
              
{
              
    return new CostBuilder();
              
}
          

So now when you call the Create.New you'll only see the builders which are in the namespaces which you referenced in your using directives.

Fair enough, upon seeing this I thought it seemed interesting, but went in to my pessimistic anti-extension method mode and came up with my usual answer, why not just do this:

public class Create
              
{
              
    public T New()  where T : new()
    {
        return new T();
    }
              
}

But upon reading this, it's pretty lame isn't it? It's basically a generic factory that doesn't new anything, why not just call new CostBuilder().DoStuff().DoMoreStuff()?

But Greg's interface is a bit cleaner than what I am offering. It's not that extension methods are really needed here, it's just that it can actually make your code a little cleaner and slightly easier to read (when working on large projects), which is something I didn't expect to say regarding extension methods.

Maybe I need to wait this one out for a year to see what kinds of things developers come up with while using extension methods.

--John Chapman