How to use LINQ in a .dib Polyglot notebook?

I’m trying to use LINQ in a C# (Polyglot Notebook).

using System.Linq;

Environment.GetEnvironmentVariables().Values.Select(x => x)

But I’m getting the error:

Error: (3,46): error CS1061: ‘ICollection’ does not contain a definition for ‘Select’ and no accessible extension method ‘Select’ accepting a first argument of type ‘ICollection’ could be found (are you missing a using directive or an assembly reference?)

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>Solution :

You don’t need the using statement, LINQ should be available/imported by default. The "issue" here is that Environment.GetEnvironmentVariables() returns a non-generic IDictionary and it’s Values property is non-generic ICollection (which implements non-generic IEnumerable) which does not support much of LINQ’s methods besides Cast, most of LINQ works with generic version of IEnumerable. So you can use Cast or OfType:

Environment.GetEnvironmentVariables().Values
    .Cast<string>() // or `OfType<string>()`
    .Select(i => i);