using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("演示值类型引用：");
            ValueTypeWarpper<int> i = 3;
            ValueTypeWarpper<int> j = 3;
            ValueTypeWarpper<int> refi = i;
            Console.WriteLine("i = {0}, j = {1}.", i, j);
            Console.WriteLine("i == j? {0}", i == j);
            refi.Value = 7;
            Console.WriteLine("i = {0}, j = {1}.", i, j);
            Console.WriteLine("i == j? {0}", i == j);
            Console.WriteLine("i > j? {0}", i > j);

            Console.WriteLine("演示值类型作为协变：");
            object[] x = new ValueTypeWarpper<int>[] { 0, 1, 2, 3, 4, 5, 6 }
                .Where(y => y % 2 == 0).ToArray();
            Console.WriteLine(string.Join(", ", x));
        }
    }

    class ValueTypeWarpper<T>
    {
        public static implicit operator T(ValueTypeWarpper<T> x)
        {
            return x.Value;
        }

        public static implicit operator ValueTypeWarpper<T>(T x)
        {
            return new ValueTypeWarpper<T>() { Value = x };
        }

        public T Value { get; set; }

        public override string ToString()
        {
            return Value.ToString();
        }

        public override bool Equals(object obj)
        {
            return obj != null
                && obj.GetType() == this.GetType()
                && Value.Equals((obj as ValueTypeWarpper<T>).Value);
        }

        public static bool operator ==(ValueTypeWarpper<T> v1, ValueTypeWarpper<T> v2)
        {
            return v1.Equals(v2);
        }

        public static bool operator !=(ValueTypeWarpper<T> v1, ValueTypeWarpper<T> v2)
        {
            return !v1.Equals(v2);
        }

        public override int GetHashCode()
        {
            return Value.GetHashCode();
        }
    }
}