Use of extension methods to enhance readability

Question

What is the general thinking on the use of extension methods that serve no purpose other than enhancing readability?

Without using extension methods we might have the method

IEnumerable<DependencyObject> GetDescendents(DependencyObject root) {}

that could be called with

var descendents = GetDescendents(someControl);

or

foreach (var descendent in GetDescendents(someControl)) {}

Although there's nothing wrong with this I find the instance.method() notation to be more readable so I might consider making this an extension method with this signature

public IEnumerable<DependencyObject> GetDescendents(this DependencyObject root) {}

allowing it to be called with

var descendents = someControl.GetDescendents();

or

foreach (var descendent in someControl.GetDescendents()) {}

So my question is whether you think this is reasonable or an abuse of extension methods. If it was simply a matter of declaring the function differently I wouldn't hesitate; but the fact that using an extension method requires it be coded in a different, static class makes me wonder if it's worth the effort or not. The example I'm using above is a fairly generic one and might have merit as an extension method that will be used in several places but often this is not the case and I would be coding the static class containing the extension in the same file as the single class that uses it.

Answer 1

Most if not all extension methods fall into this category to some degree, since they can't operate on the internals of a class anymore than your static function. At any rate, any extension method can be rewritten in a static class with an extra parameter representing the object (arguably, that's exactly what an extension method is anyway).

To me, it's entirely a question of style: in the example you provided, I'd probably jump for the extension method. I think the important question here is, Is this function something I'd write as part of the class if I were to reimplement the class, and does it make sense as such? If yes, then go for it, if no, then consider a different solution.

Answer 2

An extension method only exists to improve readability - it is merely a syntax shortcut that allows you, by specifying the this keyword on the first argument, allows you to call the method on the object instance in question. So I think it is entirely reasonable.

Answer 3

I think the big advantage of extension methods is discoverability. If someone is unaware that one of their team members created a GetDescendents method in a utility class somewhere, they'll never use it. However, if that method starts to show up in Intellisense or in the Object Browser, there's a decent chance they will stumble across it. If you start to make more extensive use of extension methods, people will start to use the tools I mentioned to look for extensions that add value.