Why can I not call ToArray on a generic IEnumerable object? [closed]

Question

public static T[] ToArray<T>(IEnumerable<T> e) {
  return e.ToArray();
}

I get the following compiler error:

Error 1 System.Collections.Generic.IEnumerable<T> does not contain a definition for ToArray and no extension method ToArray accepting a first argument of type System.Collections.Generic.IEnumerable<T> could be found (are you missing a using directive or an assembly reference?

But the MSDN reference lists this method. What is wrong here?

Answer 1

Assuming you're on .NET 3.5 or later, you need to add the using directive to the top of your code file:

using System.Linq;

You also need to have an assembly reference to System.Core (although this should be there by default for Visual Studio projects).

Answer 2

You're missing using System.Linq; at the top of the file.

ToArray is an extension method implements on IEnumerable<T> as a part of LINQ (Language-Integrated Query), so you have to add that using to make it work.