C# List Generic Extension Method vs Non-Generic

Question

This is a simple question (I hope), there are generic and non-generic methods in collection classes like List<T> that have methods such as Where and Where<T>.

Example:

        List<int> numbers = new List<int>()
        {
            1, 2, 3, 4, 5, 6, 7, 8, 9, 10
        };

        IEnumerable<int> evens = numbers.Where((x) =>
        {
            return x % 2 == 0;
        });

        IEnumerable<int> evens2 = numbers.Where<int>((x) =>
        {
            return x % 2 == 0;
        });

Why use one over the other (Generic or Non-Generic)?

Answer 1

They're the same method (documentation here). The type parameter portion after the method name (i.e. <int> in this case) is optional when the compiler is able to infer the type automatically and unambiguously from context. In this case, the method is being applied to an object implementing the interface IEnumerable<int> (i.e. the object numbers of type List<int>) from which the compiler can safely infer that the type parameter is int.

Note, also, that Where<T> is actually an extension method on the System.Linq.Enumerable class which can be applied to objects of any class implementing IEnumerable<T> such as List<T>.