匿名对象的Distinct

在使用linq distinct集合的时候，匿名对象和非匿名对象的区别非常有趣。 匿名对象自动实现了GetHashCode和Equals方法，Distinct可以自动去重。

如果使用非匿名对象，则需要该类override GetHashCode()和Equals(object obj)方法， 或者添加一个实现IEqualityComparer<T>的辅助类，作为Distinct参数。

参考下面的例子：

 #region anonymous object

            var anonymousObj1 = new
            {
                Time1 = new DateTime(2016, 10, 1),
                Time2 = new DateTime(2016, 10, 2)
            };
            var anonymousObj2 = new
            {
                Time1 = new DateTime(2016, 10, 1),
                Time2 = new DateTime(2016, 10, 2)
            };            

            Trace.WriteLine(anonymousObj1 == anonymousObj2);  // false
            Trace.WriteLine(Object.ReferenceEquals(anonymousObj1, anonymousObj2));    // false
            Trace.WriteLine(anonymousObj1.GetHashCode() == anonymousObj2.GetHashCode());  // true
            Trace.WriteLine(anonymousObj1.Equals(anonymousObj2)); // true

            #endregion

            #region non-anonymous object

            var classObj1 = new Class1
            {
                Time1 = new DateTime(2016, 10, 1),
                Time2 = new DateTime(2016, 10, 2)
            };
            var classObj2 = new Class1
            {
                Time1 = new DateTime(2016, 10, 1),
                Time2 = new DateTime(2016, 10, 2)
            };
            Trace.WriteLine(classObj1 == classObj2);  // false
            Trace.WriteLine(Object.ReferenceEquals(classObj1, classObj2));    // false
            Trace.WriteLine(classObj1.GetHashCode() == classObj2.GetHashCode());  // false
            Trace.WriteLine(classObj1.Equals(classObj2)); // false

            #endregion
            
            // distinct
            IList<Class1> list = new List<Class1>()
            {
                new Class1() {SerialNo =1, Time1 = new DateTime(2016, 10, 1),  Time2 = new DateTime(2017, 10, 1) },
                new Class1() {SerialNo =1, Time1 = new DateTime(2016, 10, 1),  Time2 = new DateTime(2017, 10, 1) },
                new Class1() {SerialNo =1, Time1 = new DateTime(2016, 10, 3),  Time2 = new DateTime(2017, 10, 10) },
                new Class1() {SerialNo =1, Time1 = new DateTime(2016, 10, 4),  Time2 = new DateTime(2017, 10, 10) }
            };

            // Count: 4. Class1 must overide GetHashCode and Equals method.
            var result1 = list.Select(p => new Class1 { Time1 = p.Time1, Time2 = p.Time2 }).Distinct();
            // Count: 3.
            var result2 = list.Select(p => new { Time1 = p.Time1, Time2 = p.Time2 }).Distinct();