This document summarizes key points about date and time data types in C#, including DateTime, DateTimeOffset, and TimeSpan. It also discusses time zones using the TimeZone and TimeZoneInfo classes, equality comparison, overriding the Equals method, and implementing the ICloneable interface. Specifically, it provides details on: - DateTime and DateTimeOffset for representing dates and times, while TimeSpan represents time intervals. - TimeZone and TimeZoneInfo classes provide information on time zones, offsets, and daylight saving rules. - Equality comparison checks value equality versus referential equality. - Overriding Equals for custom object equality checks. - The ICloneable interface allows cloning objects by

1. Lesson 9
Learn C#. Series of C# lessons
http://csharp.honcharuk.me/lesson-9

2. Agenda
• DateTime, DateTimeOffset and TimeSpan
• TimeZone and TimeZoneInfo
• Equality Comparison
• ICloneable

3. DateTime, DateTimeOffset and TimeSpan
• DateTime and DateTimeOffset are immutable structs for representing a date, and optionally, a
time. They have a resolution of 100 ns and a range covering the years 0001 through 9999
• DateTimeOffset was added in Framework 3.5 and is functionally similar to DateTime. Its
distinguishing feature is that it also stores a UTC offset; this allows more meaningful results when
comparing values across different time zones.
• TimeSpan Represents a time interval.

4. TimeZone and TimeZoneInfo
• The TimeZone and TimeZoneInfo classes provide information on time zone names UTC offsets,
and daylight saving time rules. TimeZoneInfo is the more powerful of the two and was introduced
in Framework 3.5
• The biggest difference between the two types is that TimeZone lets you access the current local
time zone, whereas TimeZoneInfo provides access to all the world’s time zones. Further,
TimeZoneInfo exposes a richer (although at times, more awkward) rules-based model for
describing daylight saving time
var bangkokTime = TimeZoneInfo.ConvertTime(DateTime.Now, TimeZoneInfo.FindSystemTimeZoneById("SE Asia Standard Time"));
Console.WriteLine("Loca time in Bangkok is: {0}", bangkokTime);

5. Equality Comparison
• Value equality: two values are equivalent in some sense
• Referential equality: two references refer to exactly the same object
int x = 5, y = 5;
Console.WriteLine(x == y);
A a1 = new A {N = 5};
A a2 = new A { N = 5 };
Console.WriteLine(a1 == a2); // False
a1 = a2;
Console.WriteLine(a1 == a2); // True

6. Equals
• null-safe equality comparison
• The double type’s == operator enforces that one NaN can never equal anything else — even
another NaN. This is most natural from a mathematical perspective, and it reflects the underlying
CPU behavior
var sb1 = new StringBuilder("foo");
var sb2 = new StringBuilder("foo");
Console.WriteLine(sb1 == sb2); // False (referential equality)
Console.WriteLine(sb1.Equals(sb2)); // True (value equality)
object x = 3, y = 3;
Console.WriteLine(object.Equals(x, y)); // True
x = null;
Console.WriteLine(object.Equals(x, y)); // False
y = null;
Console.WriteLine(object.Equals(x, y)); // True

7. Override Equals
class A
{
public int N { get; set; }
public bool Equals(A obj)
{
return obj.N == N;
}
public override bool Equals(object obj)
{
return ((A)obj).N == N;
}
}
A a1 = new A { N = 5 };
A a2 = new A { N = 5 };
Console.WriteLine(a1.Equals((object)a2));

8. ICloneable
class Book: ICloneable
{
public string Author { get; set; }
public string Title { get; set; }
public object Clone()
{
return new Book
{
Author = Author,
Title = Title
};
}
}
Book b1 = new Book
{
Author = "Tom",
Title = "Adventures"
};
Book b2 = (Book)b1.Clone();

9. Thank you!
Questions?