Simple-Type structs, Boxing and Unboxing

The data structures we discuss in this chapter store object references. However, as you will soon see, we are able to store both simple- and reference-type values in these data structures. This section discusses the mechanisms that enable simple-type values to be manipulated as objects.

Simple-Type structs

Each simple type (Appendix L, Simple Types) has a corresponding struct in namespace System that declares the simple type. These structs are called Boolean, Byte, SByte, Char, Decimal, Double, Single, Int32, UInt32, Int64, UInt64, Int16 and UInt16. Types declared with keyword struct are implicitly value types.

Simple types are actually aliases for their corresponding structs, so a variable of a simple type can be declared using either the keyword for that simple type or the struct namee.g., int and Int32 are interchangeable. The methods related to a simple type are located in the corresponding struct (e.g., method Parse, which converts a string to an int value, is located in struct Int32). Refer to the documentation for the corresponding struct type to see the methods available for manipulating values of that type.

Boxing and Unboxing Conversions

All simple-type structs inherit from class ValueType in namespace System. Class ValueType inherits from class object. Thus, any simple-type value can be assigned to an object variable; this is referred to as a boxing conversion. In a boxing conversion, the simple-type value is copied into an object so that the simple-type value can be manipulated as an object. Boxing conversions can be performed either explicitly or implicitly as shown in the following statements:

int i = 5; // create an int value
object object1 = ( object ) i; // explicitly box the int value
object object2 = i; // implicitly box the int value

After executing the preceding code, both object1 and object2 refer to two different objects that contain a copy of the integer value in int variable i.

An unboxing conversion can be used to explicitly convert an object reference to a simple value as shown in the following statement:

int int1 = ( int ) object1; // explicitly unbox the int value

Explicitly attempting to unbox an object reference that does not refer to the correct simple value type causes an InvalidCastException.

In Chapter 26, Generics, and Chapter 27, Collections, we discuss C#'s generics and generic collections. As you will see, generics eliminate the overhead of boxing and unboxing conversions by enabling us to create and use collections of specific value types.


Preface

Index

    Introduction to Computers, the Internet and Visual C#

    Introduction to the Visual C# 2005 Express Edition IDE

    Introduction to C# Applications

    Introduction to Classes and Objects

    Control Statements: Part 1

    Control Statements: Part 2

    Methods: A Deeper Look

    Arrays

    Classes and Objects: A Deeper Look

    Object-Oriented Programming: Inheritance

    Polymorphism, Interfaces & Operator Overloading

    Exception Handling

    Graphical User Interface Concepts: Part 1

    Graphical User Interface Concepts: Part 2

    Multithreading

    Strings, Characters and Regular Expressions

    Graphics and Multimedia

    Files and Streams

    Extensible Markup Language (XML)

    Database, SQL and ADO.NET

    ASP.NET 2.0, Web Forms and Web Controls

    Web Services

    Networking: Streams-Based Sockets and Datagrams

    Searching and Sorting

    Data Structures

    Generics

    Collections

    Appendix A. Operator Precedence Chart

    Appendix B. Number Systems

    Appendix C. Using the Visual Studio 2005 Debugger

    Appendix D. ASCII Character Set

    Appendix E. Unicode®

    Appendix F. Introduction to XHTML: Part 1

    Appendix G. Introduction to XHTML: Part 2

    Appendix H. HTML/XHTML Special Characters

    Appendix I. HTML/XHTML Colors

    Appendix J. ATM Case Study Code

    Appendix K. UML 2: Additional Diagram Types

    Appendix L. Simple Types

    Index



    Visual C# How to Program
    Visual C# 2005 How to Program (2nd Edition)
    ISBN: 0131525239
    EAN: 2147483647
    Year: 2004
    Pages: 600

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