Program.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Linq;
using System.Reflection;
using System.Reflection.Emit;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;
using TriangleNet;
using TriangleNet.Geometry;

namespace Testing
{
	class Choice<TOut, TIn>
	{
		public TOut Value;
		private Func<TIn, bool>[] conditions;

		public Choice(TOut value, params Func<TIn, bool>[] conditions)
		{
			this.Value = value;
			this.conditions = conditions;
		}

		public bool ConditionMet(TIn target)
		{
			return conditions.Any(f => f(target));
		}
	}

	class Checker<TOut, TIn>
	{
		public TIn Target;
		public List<Choice<TOut, TIn>> Choices;

		public Checker(TIn target)
		{
			Target = target;
		}

		public Checker<TOut, TIn> AppendChoice(TOut value, params Func<TIn, bool>[] conditions)
		{
			var choice = new Choice<TOut, TIn>(value, conditions);
			var checker = new Checker<TOut, TIn>(Target);
			checker.Choices =Choices == null ? new List<Choice<TOut, TIn>>() : new List<Choice<TOut, TIn>>(Choices);
			checker.Choices.Add(choice);

			return checker;
		}

		public TOut GetValue()
		{
			return Choices.First(c => c.ConditionMet(Target)).Value;
		}
	}

	class Program
	{
		static void Main(string[] args)
		{
			int a = 10;

			bool aVeceOd5 = a.Check<bool, int>()
				.AppendChoice(
					false,
					x => x == 1,
					x => x == 2,
					x => x == 3,
					x => x == 4,
					x => x == 5
				).AppendChoice(
					true,
					x => x > 5
				).GetValue();

			Console.WriteLine(aVeceOd5);


			Console.ReadKey();
		}

		static TOut GetCorrectValue<TOut, TIn>(TIn target, params Choice<TOut, TIn>[] choices)
		{
			return choices.First(choice => choice.ConditionMet(target)).Value;
		}
	}

	static class Extensions
	{
		public static Checker<TOut, TIn> Check<TOut, TIn>(this TIn target)
		{
			return new Checker<TOut, TIn>(target);
		}
	}
}