using System;

using System.Collections.Generic;

using System.Linq;

using System.Net.Configuration;

using System.Net.Sockets;

using System.Text;

using System.Threading.Tasks;

​

namespace Practice

{

  public class Person

  {

    public String FirstName { get; set; }

​

    public String LastName { get; set; }

​

    public DateTime BirthDate { get; set; }

​

    public Address Address { get; set; }

  }

​

  public class Address

  {

    public String Location { get; set; }

​

    public Int32 PostCode { get; set; }

  }

​

  public static class ObjectUtils

  {

    // Solution #1

    //public static TResult Safe<TElement, TResult>(this TElement element, Func<TElement, TResult> selector)

    //  where TElement : class

    //{

    //  if (element != null) return selector(element);

    //  return default(TResult);

    //}

​

    public static TResult Safe<TElement, TResult>(this TElement element, Func<TElement, TResult> selector)

      where TElement : class

      where TResult : class

    {

      if (element != null) return selector(element);

      return default(TResult);

    }

​

    public static TResult Safe<TElement, TResult>(this Nullable<TElement> element, Func<TElement, TResult> selector)

      where TElement : struct

    {

      if (element.HasValue) return selector(element.Value);

      return default(TResult);

    }

​

    public static Nullable<TResult> SafeValue<TElement, TResult>(this TElement element, Func<TElement, TResult> selector)

      where TElement : class

      where TResult : struct

    {

      if (element != null) return selector(element);

      return null;

    }

​

    public static Nullable<TResult> SafeValue<TElement, TResult>(this Nullable<TElement> element, Func<TElement, TResult> selector)

      where TElement : struct

      where TResult : struct

    {

      if (element.HasValue) return selector(element.Value);

      return null;

    }

  }

​

  public class Program

  {

    // Solution #1

    //public static String GetCityName(Person person)

    //{

    //  if (person != null &&

    //      person.Address != null &&

    //      person.Address.City != null)

    //  {

    //    var city = person.Address.City.Split('-').FirstOrDefault();

    //    if (city != null) return city;

    //  }

​

    //  return String.Empty;

    //}

​

    // Solution #2

    //private static String GetLocationOrDefault(Person person)

    //{

    //  if (person != null &&

    //      person.Address != null &&

    //      person.Address.City != null)

    //    return person.Address.City;

​

    //  return null;

    //}

​

    // Solution #3

    //public static String GetCityName(Person person)

    //{

    //  var location = GetLocationOrDefault(person);

    //  if (location != null)

    //  {

    //    var city = location.Split('-').FirstOrDefault();

    //    if (city != null) return city;

    //  }

​

    //  return String.Empty;

    //}

​

    // Solution #4

    //public static String GetCityName(Person person)

    //{

    //  var city = person.Safe(p => p.Address)

    //                   .Safe(address => address.Location)

    //                   .Safe(location => location.Split('-'))

    //                   .Safe(values => values.FirstOrDefault());

​

    //  return city ?? String.Empty;

    //}

​

    // Solution #5

    //public static String GetCityName(Person person)

    //{

    //  var city = person?.Address?.Location?.Split('-')?.FirstOrDefault();

    //  return city ?? String.Empty;

    //}

​

    // Solution #6

    //public static String GetCityName(Person person)

    //{

    //  var city = person?.Address?.Location?.Split('-')?[0];

    //  return city ?? String.Empty;

    //}

​

    public static Int32? GetPostCode(Person person)

    {

      var postcode = person.Safe(p => p.Address)

                           .SafeValue(address => address.PostCode);

      return postcode;

    }

​

    private static void Main(string[] args)

    {

      Person person = new Person

      {

        FirstName = "John",

        LastName = "Doe",

        BirthDate = DateTime.Now.AddYears(-10),

        Address = new Address

        {

          Location = "Budapest - Lehel út 13.",

          PostCode = 1134

        }

      };

​

      Console.WriteLine(GetPostCode(null));

      Console.ReadKey();

    }

  }

}