Where is the ToObservable extension method?

I see it mentioned here, but I can't work out which using I have to add to get it.

(Rolled my own 开发者_JAVA技巧for the moment)

It is in:

using System.Reactive.Linq;

You need to add reference to System.Reactive.dll. Then in code write:

using System.Linq;

UPDATE: Now Rx is available as separate extensions. There are 3 versions of Rx: Rx for .NET 3.5 Sp1, Rx for Silverlight 3 and Rx for .NET 4 Beta 2. All 3 versions can be downloaded from the Devlabs Rx project page.

You need install Nuget-package System.Reactive.Linq