using System;using System.Collections.Generic;using System.Linq;namespace Validation // include rules in the domain that may vary from instance to instance{    class Program    {        static void Main(string[] args)        {            var memberEoo = new Member { Name = "EooName", Area = "Eoo", Age = 15, Email = string.Empty }; // Eoo member must be at least 18            foreach (var item in memberEoo.Validate())            {                Console.WriteLine(item);            }            var memberFoo = new Member { Name = "FooName", Area = "Foo", Age = 15, Email = string.Empty }; // Foo member must have an email            foreach (var item in memberFoo.Validate())            {                Console.WriteLine(item);            }        }    }    public class Member // domain model    {        private readonly List
     
       _ruleItems = new List
      
       (); // broken rules        public string Name { get; set; }        public string Area { get; set; }        public int Age { get; set; }        public string Email { get; set; }        public List
       
         Validate()        {            if (string.IsNullOrEmpty(Name))            {                _ruleItems.Add("member must have a name");            }            if (string.IsNullOrEmpty(Area))            {                _ruleItems.Add("member must have an area");            }            else            {                _ruleItems.AddRange(RuleFactory.GetRule(Area).GetRuleItems(this)); // specific rules            }            return _ruleItems;        }    }    public abstract class Rule    {        public abstract string Area { get; }        public abstract IEnumerable
        
          GetRuleItems(Member member);    }    public class EooRule : Rule    {        public override string Area => "Eoo";        public override IEnumerable
         
           GetRuleItems(Member member)        {            var ruleItems = new List
          
           (); if (member.Age < 18) { ruleItems.Add("Eoo member must be at least 18"); } return ruleItems; } } public class FooRule : Rule { public override string Area => "Foo"; public override IEnumerable
           
             GetRuleItems(Member member) { var ruleItems = new List
            
             (); if (string.IsNullOrEmpty(member.Email)) { ruleItems.Add("Foo member must have an email"); } return ruleItems; } } public class RuleFactory { private static readonly List
             
               _rules = new List
              
                { new EooRule(), new FooRule() }; public static Rule GetRule(string area) { return _rules.FirstOrDefault(v => v.Area == area); } }}