C# 4 and .NET 4

namespaces ❘ 45
}
}
{
}
case TimeOfDay.Morning:
Console.WriteLine("Good morning!");
break;
case TimeOfDay.Afternoon:
Console.WriteLine("Good afternoon!");
break;
case TimeOfDay.Evening:
Console.WriteLine("Good evening!");
break;
default:
Console.WriteLine("Hello!");
break;
The real power of enums in C# is that behind the scenes they are instantiated as structs derived from the
base class, System.Enum. This means it is possible to call methods against them to perform some useful
tasks. Note that because of the way the .NET Framework is implemented there is no performance loss
associated with treating the enums syntactically as structs. In practice, after your code is compiled, enums
will exist as primitive types, just like int and float.
You can retrieve the string representation of an enum as in the following example, using the earlier
TimeOfDay enum:
TimeOfDay time = TimeOfDay.Afternoon;
Console.WriteLine(time.ToString());
This will return the string Afternoon.
Alternatively, you can obtain an enum value from a string:
TimeOfDay time2 = (TimeOfDay) Enum.Parse(typeof(TimeOfDay), "afternoon", true);
Console.WriteLine((int)time2);
This code snippet illustrates both obtaining an enum value from a string and converting to an integer.
To convert from a string, you need to use the static Enum.Parse() method, which, as shown, takes three
parameters. The first is the type of enum you want to consider. The syntax is the keyword typeof followed
by the name of the enum class in brackets. (Chapter 7 explores the typeof operator in more detail.) The
second parameter is the string to be converted, and the third parameter is a bool indicating whether you
should ignore case when doing the conversion. Finally, note that Enum.Parse() actually returns an object
reference — you need to explicitly convert this to the required enum type (this is an example of an unboxing
operation). For the preceding code, this returns the value 1 as an object, corresponding to the enum value of
TimeOfDay.Afternoon. On converting explicitly to an int, this produces the value 1 again.
Other methods on System.Enum do things such as return the number of values in an enum definition or list
the names of the values. Full details are in the MSDN documentation.
namesPaCes
As you saw earlier in this chapter, namespaces provide a way of organizing related classes and other types.
Unlike a file or a component, a namespace is a logical rather than physical grouping. When you define a
class in a C# file, you can include it within a namespace definition. Later, when you define another class
that performs related work in another file, you can include it within the same namespace, creating a logical
grouping that gives an indication to other developers using the classes how they are related and used:
namespace CustomerPhoneBookApp
{
using System;
public struct Subscriber
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