C# Generic

using System;
 
namespace ConsoleApp4
{
    class Program
    {
        static void Main(string[] args)
        {
            var book = new Book() {Isbn = "1111", Title = "C# Advanced"};
            //var numbers = new List();
            //numbers.Add(10);
 
            //var books = new BookList();
            //books.Add(book);
 
            //var number = new GenericList<int>();
            //number.Add(10);
 
            //var books = new GenericList<Book>();
            //books.Add(new Book());
 
            //var dictionary = new GenericDictionary<string, Book>();
            //dictionary.Add("1234", new Book());
 
            var number = new ConsoleApp4.Nullable<int>();
            Console.WriteLine("HasValue: " + number.HasValue);
            Console.WriteLine("Value: " + number.GetValueOrDefault());
 
            Console.ReadKey();
 
        }
    }
}
 

using System;
using System.Collections.Generic;
using System.Text;
 
namespace ConsoleApp4
{
    public class List
    {
        public void Add(int number)
        {
            throw new NotImplementedException();
        }
 
        public int this[int index]
        {
            get { throw new NotImplementedException(); }
        }
    }
}
 

using System;
 
namespace ConsoleApp4
{
    public class BookList
    {
        public void Add(Book book)
        {
            throw new NotImplementedException();
        }
 
        public Book this[int index]
        {
            get { throw new NotImplementedException(); }
        }
    }
}

namespace ConsoleApp4
{
    public class Book
    {
        public string Isbn { get; set; }
        public string Title { get; set; }
    }
}

using System;
 
namespace ConsoleApp4
{
    public class GenericList<T>
    {
        public void Add(T value)
        {
 
        }
 
        public T this[int index]
        {
            get { throw  new NotImplementedException(); }
        }
    }
 
    public class GenericDictionary<TKey, TValue>
    {
        public void Add(TKey key, TValue value)
        {
 
        }
    }
}

namespace ConsoleApp4
{
    public class Nullable<T> where T : struct
    {
        private object _value;
 
        public Nullable()
        {
            
        }
 
        public Nullable(T value)
        {
            _value = value;
        }
 
        public bool HasValue
        {
            get { return _value != null; }
        }
 
        public T GetValueOrDefault()
        {
            if (HasValue)
            {
                return (T)_value;   //unboxing
            }
 
            return default(T);
        }
    }
}

using System;
 
namespace ConsoleApp4
{
    // where T : IComparable        interface
    // where T : Product            sub classes
    // where T : struct             value type
    // where T : class              reference type
    // where T : new()              default constructor
    public class Utilities<T> where  T : IComparable, new()
    {
        public int Max(int a, int b)
        {
            return a > b ? a : b;
        }
 
        //public T Max<T>(T a, T b) where T : IComparable
        //{
        //    return a.CompareTo(b) > 0 ? a : b;
        //}
 
        public T Max(T a, T b)
        {
            return a.CompareTo(b) > 0 ? a : b;
        }
 
        public void DoSomething(T value)
        {
            var obj = new T();
        }
    }
}

namespace ConsoleApp4
{
    public class DiscountCalculator<TProduct> where TProduct : Product
    {
        public float CalculateDiscount(TProduct product)
        {
            return product.Price;
        }
    }
}

namespace ConsoleApp4
{
    public class Product
    {
        public string Title { get; set; }
        public float Price { get; set; }
    }
}