The associated value of an enum member is assigned either implicitly or explicitly. If the declaration of the enum member has a constant-expression initializer, the value of that constant expression, implicitly converted to the underlying type of the enum, is the associated value of the enum member. If the declaration of the enum member has no initializer, its associated value is set implicitly, as follows:
• If the enum member is the first enum member declared in the enum type, its associated value is zero.
• Otherwise, the associated value of the enum member is obtained by increasing the associated value of the previous enum member by one. This increased value must be within the range of values that can be represented by the underlying type.
The example
using System;
234
Copyright  Microsoft Corporation 1999-2000. All Rights Reserved.
Chapter 14 Enums
enum Color
{
Red,
Green = 10,
Blue
}
class Test
{
static void Main() {
Console.WriteLine(StringFromColor(Color.Red));
Console.WriteLine(StringFromColor(Color.Green));
Console.WriteLine(StringFromColor(Color.Blue));
}
static string StringFromColor(Color c) {
switch (c) {
case Color.Red:
return String.Format("Red = {0}", (int) c);
case Color.Green:
return String.Format("Green = {0}", (int) c);
case Color.Blue:
return String.Format("Blue = {0}", (int) c);
default:
return "Invalid color";
}
}
}
prints out the enum member names and their associated values. The output is:
Red = 0
Blue = 10
Green = 11
for the following reasons:
• the enum member Red is automatically assigned the value zero (since it has no initializer and is the first enum member);
• the enum member Blue is explicitly given the value 10;
• and the enum member Green is automatically assigned the value one greater than the member that textually precedes it.
The associated value of an enum member may not, directly or indirectly, use the value of its own associated enum member. Other than this circularity restriction, enum member initializers may freely refer to other enum member initializers, regardless of their textual position. Within an enum member initializer, values of other enum members are always treated as having the type of their underlying type, so that casts are not necessary when referring to other enum members.
The example
enum Circular
{
A = B
B
}
is invalid because the declarations of A and B are circular. A depends on B explicitly, and B depends on A implicitly.
Copyright  Microsoft Corporation 1999-2000. All Rights Reserved.
235
C# LANGUAGE REFERENCE
Enum members are named and scoped in a manner exactly analogous to fields within classes. The scope of an enum member is the body of its containing enum type. Within that scope, enum members can be referred to by their simple name. From all other code, the name of an enum member must be qualified with the name of its enum type. Enum members do not have any declared accessibility—an enum member is accessible if its containing enum type is accessible.
14.3 Enum values and operations Each enum type defines a distinct type; an explicit enumeration conversion (§6.2.2) is required to convert between an enum type and an integral type, or between two enum types. The set of values that an enum type can take on is not limited by its enum members. In particular, any value of the underlying type of an enum can be cast to the enum type, and is a distinct valid value of that enum type.
Enum members have the type of their containing enum type (except within other enum member initializers: see
§14.2). The value of an enum member declared in enum type E with associated value v is (E)v.
The following operators can be used on values of enum types: ==, !=, <, >, <=, >= (§7.9.5), + (§7.7.4),
- (§7.7.5), ^, &, | (§7.10.2), ~ (§7.6.4), ++, -- (§7.5.9, §7.6.7), sizeof (§7.5.12).
Every enum type automatically derives from the class System.Enum. Thus, inherited methods and properties of this class can be used on values of an enum type.
236
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Chapter 15 Delegates
15. Delegates
15.1 Delegate declarations delegate-declaration: attributesopt delegate-modifiersopt delegate result-type identifier ( formal-parameter-listopt
) ;
15.1.1 Delegate modifiers
delegate-modifiers:
delegate-modifier
delegate-modifiers delegate-modifier
delegate-modifier:
new
public
protected
internal
private
Copyright  Microsoft Corporation 1999-2000. All Rights Reserved.
237
Chapter 16 Exceptions
16. Exceptions Copyright  Microsoft Corporation 1999-2000. All Rights Reserved.
239
Chapter 17 Attributes
17. Attributes Much of the C# language enables the programmer to specify declarative information about the entities defined in the program. For example, the accessibility of a method in a class is specified by decorating it with the method-modifiers public, protected, internal, and private.