Question

Is there any way to express this idea in C#? (Basically a generic type of a generic type)?

public static class ExtensionSpike
{
    public static IEnumerable<T> Where<TCollection<T>>(this TCollection<T> sourceCollection, Expression<Func<T, bool>> expr)
        where TCollection : class, IEnumerable<T>, INotifyCollectionChanged
    {
        throw new NotImplementedException();
    }
}

Answer 1

The generic constraint might not be quite what you want, but is this basically what you’re looking for? This constrains TCollection to be an IEnumerable<T> (although IEnumerable can be swapped for List/Collection/Etc…)

public static IEnumerable<T> Where<T, TCollection>(this TCollection sourceCollection, Expression<Func<T, bool>> expr)
where TCollection : IEnumerable<T>, INotifyPropertyChanged
{
    throw new NotImplementedException();
}

Update: just changed my sample a little to better follow the method–I’d been confused and didn’t realize you wanted a Where() method, I assumed it was your generic-constraint where.