using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program {

    public static IEnumerable<T> ToEnumerable1 <T> (T v) {

        yield return v;

    }

    public static T[] ToEnumerable2 <T> (params T[] vs) => vs;

    public static void Main () {

        static IEnumerable<T> ToEnumerable3 <T> (params T[] v) => v;

        p( new string[] { "three" } );

        p( new List<string> { "three" } );

        p( ToEnumerable1("three") ); // our utility function (yield return)

        p( ToEnumerable2("three") ); // our utility function (params)

        p( ToEnumerable3("three") ); // our local utility function (params)

        p( Enumerable.Empty<string>().Append("three") );

        p( Enumerable.Empty<string>().DefaultIfEmpty("three") );

        p( Enumerable.Empty<string>().Prepend("three") );

        p( Enumerable.Range(3, 1) ); // only for int

        p( Enumerable.Range(0, 1).Select(_ => "three") );

        p( Enumerable.Repeat("three", 1) );

        p( "_".Select(_ => "three") ); // doesn't have to be "_"; just any one character

        p( "_".Select(_ => 3.3333) );

        p( from _ in "_" select 3.0f );

        p( "a" ); // only for char

        // these weren't available for me to test (might not even be valid):

        //   new Microsoft.Extensions.Primitives.StringValues("three")

    }

​

    static void p <T> (IEnumerable<T> e) =>

        Console.WriteLine(string.Join(' ', e.Select((v, k) => $"[{k}]={v,-8}:{v.GetType()}").DefaultIfEmpty("<empty>")));

​

}