C# List: why you cannot do `List foo = new List();`

Question

If you have an Interface IFoo and a class Bar : IFoo, why can you do the following:

List foo = new List();          


        

Answer 1

If you need to convert a list to a list of a base class or interface you can do this:

using System.Linq;

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List bar = new List();
bar.add(new Bar());

List foo = bar.OfType().ToList();