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CSharp · Console

/Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
					
public class Program
{
	public static void Main()
	{
		var range = Enumerable.Range(1, 10);
		Console.WriteLine(EnumerableFunctor.Map(range, x => x).SequenceEqual(range)); // выведет True

		int? nullableTen = 10;
		int? nullableNull = null;
		Console.WriteLine(NullableFunctor.Map(nullableTen, x => x) == nullableTen); // выведет True
		Console.WriteLine(NullableFunctor.Map(nullableNull, x => x) == nullableNull); // выведет True
	}
}

public static class EnumerableFunctor
{
	public static IEnumerable<B> Map<A, B>(IEnumerable<A> source, Func<A, B> map) =>
		source.Select(map);
}

public static class NullableFunctor
{
	public static B? Map<A, B>(A? source, Func<A, B> map) where A : struct where B : struct =>
		source is A notNullSource ? map(notNullSource) : default(B?);
}