Now that you have seen a number of variations on the C# indexer method, you may be wondering how this

Apr ss © 2003 (1200 pages)

member is represented in terms of raw CIL. If you were to open up the numerical indexer of the Cars type,

This comprehensive text starts with a brief overview of the you would find thatC#thelanguageC# compilerand thenhasquicklycreatedmovesa propertyto key namedtechnicalItem:and

architectural issues for .NET developers.

.property instance class Indexer.Car Item(int32)

{

Table of Contents

.get instance class Indexer.Car Indexer.Cars::get_Item(int32)

C# and the .NET Platform, Second Edition

.set instance void Indexer.Cars::set_Item(int32,

Introduction

class Indexer.Car)

Part One - Introducing C# and the .NET Platform

} // end of property Cars::Item

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

Part Two - The C# Programming Language

ChapterNow, if3you- haveC# LanguagebackgroundFundamentalsin the Visual Basic programming language, you may be happy to see that Chapterthe internal4 - representationObject-OrientedofProgrammingC# indexerwithis indeedC# a property named Item. The reason (for those who

are not aware of various VB-isms) is that VB types that provide access to subtypes typically define a

Chapter 5 - Exceptions and Object Lifetime

default method named Item. In the world of VB, a default item identifies the method to be called on a type

Chapter 6 - Interfaces and Collections

if the caller does not explicitly specify it by name, but rather makes use of the index notation (which under

Chapter 7 - Callback Interfaces, Delegates, and Events

VB is denoted as () rather than []). Given this factoid, understand that C# indexers are CLS compliant, and

Chapter 8 - Advanced C# Type Construction Techniques

can be called from any .NET-aware programming language.

Part Three - Programming with .NET Assemblies

Chapter 9 - Understanding .NET Assemblies

Note FYI, unlike VB 6.0, VB .NET will only allow you to define a default property that has at least one

Chapter 10 - Processes, AppDomains, Contexts, and Threads

parameter. Given this, the VB 6.0 "Set" keyword is now obsolete.

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Chapter 14 - A Better Painting Framework (GDI+)

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

Index

List of Figures

List of Tables

Using the C# aIndexerd the .NETfromPlatform,VBSecond.NETEdition

To illustrate the language-agnostic nature of C# indexers requires an understanding of .NET code libraries

Apress © 2003 (1200 pages)

(e.g., custom *.dll assemblies). The next chapter will examine this process in great detail, so for the time

This comprehensive text starts with a brief overview of the

being simply assumeC# languageyou haveandcreatedthen quicklya C# codemoveslibraryto keynamedtechnicalIndexerCodeLibraryand that contains the Cars, Radio, andarchitecturalCar types. Ifissuesa VB .forNET.NETapplicationdeveloperswere. to set a reference to this external assembly, it would be able to interact with the contained types as follows:

Table of Contents

' The VB .NET 'Imports' keyword is

C# and the .NET Platform, Second Edition

' the same as the C# 'using' keyword.

Introduction

Imports IndexerCodeLibrary

List of Tables

OverloadingC#Operatorsand the .NET Platform, Second Edition

So much for the topic of C# indexers. Next up, we will examine a technique that is not supported by all

Apress © 2003 (1200 pages)

.NET-aware programming languages, but is useful nonetheless. C#, like any programming language, has

This comprehensive text starts with a brief overview of the

a canned set of tokensC# languthatgeareandusedthentoquicklyperformovesbasictooperationskey technicalon andintrinsic types. For example, everyone knows that the + architecturoperator canl issuesbe appliedfor .NETto twodevelopersintegers. in order to yield a new integer:

// The + operator in action.

Table of Contents int a = 100;

C# and the .NET Platform, Second Edition int b = 240;

Introduction

int c = a+b; // c is now 340

Part One - Introducing C# and the .NET Platform

Chapter 1 - The Philosophy of .NET

ChapterThis is 2no -majorBuildingnewsC#flash,Applicationsbut have you ever stopped and noticed how the same + operator can be

Pappliedrt Two to- TheanyC#intrinsicProgrammingC# dataLanguagetype? For example:

Chapter 3 - C# Language Fundamentals

Chapter 4 - Object-Oriented Programming with C#

// + operator with strings.

Chapter 5 - Exceptions and Object Lifetime

string s1 = "Hello";

Chapterstring6 s2- Interfaces= " world!";and Collections

Chapterstring7 s3- Callback= s1 Interfaces,+ s2; //Delegates,s3 is nowand Events"Hello world!"

Chapter 8 - Advanced C# Type Construction Techniques

Part Three - Programming with .NET Assemblies

In essence, the + operator has been overloaded to function correctly on various individual data types.

Chapter 9 - Understanding .NET Assemblies

When the + operator is applied to numerical types, the result is the summation of the operands. However,

Chapter 10 - Processes, AppDomains, Contexts, and Threads

when applied to string types, the result is string concatenation.

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Part Four - Leveraging the .NET Libraries

Note Understand that unlike numerous types in the .NET base class libraries, the intrinsic data types

Chapter 12 - Object Serialization and the .NET Remoting Layer

of the System namespace have not literally overloaded the set of C# operators, as CIL provides

Chapter 13 - Building a Better Windowmanipulation(Introduci g Windows Forms) specific opcodes for the of numeric data types.

Chapter 14 - A Better Painting Framework (GDI+)

The C# language (like C++ and unlike Java) provides the capability for you to build custom classes and

Chapter 15 - Programming with Windows Forms Controls

structures that also respond uniquely to the same set of basic tokens (such as the + operator). To

Chapter 16 - The System.IO Namespace

illustrate, assume the following simple Point structure (and yes, you are able to overload operators on

Chapter 17 - Data Access with ADO.NET

class types as well):

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

// Just a simple everyday C# struct.

Chapter 19 - ASP.NET Web Applications

public struct Point

Chapter 20 - XML Web Services

{

Index

private int x, y;

List of Figures

public Point(int xPos, int yPos)

List of Tables

{

x = xPos; y = yPos;

}

public override string ToString()

{

return string.Format("X pos: {0} Y pos: {1}", this.x, this.y);

}

}

Now, logically speaking, it makes sense to add Points together. On a related note, it would be helpful to subtract one Point from another. For example, if you created two Point objects with some initial startup values, you may like to do something like this:

// Adding and subtracting two points.

C# and the .NET Platform, Second Edition public static int Main(string[] args)

This comprehensive text starts with a brief overview of the

Point ptOne = new Point(100, 100);

C# language and then quickly moves to key technical and

Point ptTwo = new Point(40, 40); architectural issues for .NET developers.

// Add the points to make a new point.

Point bigPoint = ptOne + ptTwo;

Console.WriteLine("Here is the big point: {0} ", bigPoint.ToString());

Table of Contents

// Subtract the points to make a new point.

C# and the .NET Platform, Second Edition

Point minorPoint = bigPoint - ptOne;

Introduction

Console.WriteLine("Just a minor point: {0} ", minorPoint.ToString());

Part One - Introducing C# and the .NET Platform

return 0;

Chapter 1 - The Philosophy of .NET

}

Chapter 2 - Building C# Applications

Part Two - The C# Programming Language

ChapterClearly,3your- C#goalLanguageis to somehowFundamentalsmake your Point type react uniquely to the + and – operators. To allow a

Chaptercustom4type- Objectto respond-OrientoedtheseProgrammingintrinsic tokens,with C#C# provides the "operator" keyword, which can only be

Chapterused in5conjunction- ExceptionswithandstaticObjectmethodsLifetime. To illustrate:

Chapter 6 - Interfaces and Collections

Chapter 7 - Callback Interfaces, Delegates, and Events

// A more intelligent Point type.

Chapterpublic8 struct- AdvancedPointC# Type Construction Techniques

Part{ Three - Programming with .NET Assemblies

Chapter private9 - Und rstandingint x,.NETy; Assemblies

Chapter public10 - Processes,Point(intAppDomains,xPos,Contexts,int yPos){and Threadsx = xPos; y = yPos; }

// The Point type can be added...

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

public static Point operator + (Point p1, Point p2)

Part Four - Leveraging the .NET Libraries

{

Chapter 12 - Object Serialization and the .NET Remoting Layer

Point newPoint = new Point(p1.x + p2.x, p1.y + p2.y);

Chapter 13 - Building a Better Window (Introducing Windows Forms)

return newPoint;

Chapter 14 - A Better Painting Framework (GDI+)

}

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

public static Point operator - (Point p1, Point p2)

Chapter 17 - Data Access with ADO.NET

{

Part Five - Web Applications and XML Web Services

// Figure new X (assume [0,0] base).

}

public override string ToString()

{

return string.Format("X pos: {0} Y pos: {1}", this.x, this.y);

}

}

Notice that the class now contains two strange looking methods called operator + and operator –.The logic behind operator + is simply to return a brand new Point based on the summation of the incoming Point arguments. Thus, when you write pt1 + pt2, under the hood you can envision the following hidden call to the static operator + method:

This comprehensive text starts with a brief overview of the

Likewise, p1 – p2 maps to the following:

C# language and then quickly moves to key technical and architectural issues for .NET developers.

// p3 = Point.operator- (p1, p2)

p3 = p1 - p2;

Table of Contents

C# and the .NET Platform, Second Edition

Introduction

Part One - Introducing C# and the .NET Platform

Overloading the Equality Operators

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

As you may recall, System.Object.Equals() can be overridden in order to perform valuebased (rather than

Part Two - The C# Programming Language

referenced-based) comparisons between objects. In addition to overriding Equals() and GetHashCode(),

Chapter 3 - C# Language Fundamentals

an object may choose to override the equality operators (= = and !=). To illustrate, here is the updated

Chapter 4 - Object-Oriented Programming with C#

Point type:

Chapter 5 - Exceptions and Object Lifetime

Chapter 6 - Interfaces and Collections

// This incarnation of Point also overloads the == and != operators.

Chapter 7 - Callback Interfaces, Delegates, and Events public struct Point

Chapter 8 - Advanced C# Type Construction Techniques

{

Part Three - Programming with .NET Assemblies

public int x, y;

Chapter 9 - Understanding .NET Assemblesint

public Point(int xPos, yPos){ x = xPos; y = yPos;}

Chapter... 10 - Processes, AppDomains, Contexts, and Threads

Chapter public11 - TypeoverrideReflect on, LateboolBinding,Equals(objectand Attribute-Basedo) Programming

Part Four{- Leveraging the .NET Libraries

Chapter 12 - Objectif((Serialization(Point)o)and.xthe=.NET= thisRemoting.x &&Layer

((Point)o).y = = this.y)

Chapter 13 - Building a Better Window (Introducing Windows Forms)

return true;

Chapter 14 - A Better Painting Framework (GDI+)

else

Chapter 15 - Programming with Windows Forms Controls

return false;

Chapter 16 - The System.IO Namespace

}

Chapter 17 - Data Access with ADO.NET

public override int GetHashCode()

Part Five - Web Applications and XML Web Services

{ return this.ToString().GetHashCode(); }

Chapter 18 - ASP.NET Web Pages and Web Controls

// Now let's overload the == and != operators.

Chapter 19 - ASP.NET Web Applications

public static bool operator ==(Point p1, Point p2)

Chapter 20 - XML Web Services

{ return p1.Equals(p2); }

Index public static bool operator !=(Point p1, Point p2)

List of Figures

{ return !p1.Equals(p2); }

List of Tables

}

Notice how the implementation of operator == and operator != simply makes a call to the overridden Equals() method to get the bulk of the work done. Given this, you can now exercise your Point class as follows:

// Make use of the overloaded equality operators. public static int Main(string[] args)

{

...

Console.WriteLine("These are not equal.");

}Apress © 2003 (1200 pages)

This comprehensive text starts with a brief overview of the C# language and then quickly moves to key technical and

architectural issues for .NET developers.

As you can see, it is quite intuitive to compare two objects using the well-known == and != operators rather than making a call to Object.Equals(). As a rule of thumb, classes that override

Object.Equals()/Object.GetHashCode() should always overload the == and != operators.

Table of Contents

C#If youanddotheoverload.NET Platform,the equalitySecondoperatorsEdition for a given class, keep in mind that C# demands that if you

Introductionoverride operator ==, you must also override operator !=, just as when you override Equals() you will need

Partto overrideOne - IntroducingGetHashCode()C# and. Thist e .NETensuresPlatformthat an object behaves in a uniform manner during comparisons

Chapterand functions1 - ThecorrectlyPhilosophyif placedof .NETinto a hash table (if you forget, the compiler will let you know).

Chapter 2 - Building C# Applications

SOURCE The OverLoadOps project is located under the Chapter 8 subdirectory.

Part Two - The C# Programming Language

CODE

Chapter 3 - C# Language Fundamentals

Chapter 4 - Object-Oriented Programming with C#

ChaptOverloadingr 5 - ExceptionstheandComparisonObject Lifetime Operators

Chapter 6 - Interfaces and Collections

InChapter 6, you learned how to implement the IComparable interface in order to compare the relative

Chapter 7 - Callback Interfaces, Delegates, and Events

relationship between two like objects. Additionally, you may also overload the comparison operators (<, >, <=, and >=) for the same class. Like the equality operators, C# demands that < and > are overloaded as a set. The same holds true for the <= and >= operators. If the Car type you developed in Chapter 6

overloaded these comparison operators, the object user could now compare types as follows:

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

// Exercise the overloaded < operator for the Car class.

Part Four - Leveraging the .NET Libraries

public class CarApp

Chapter 12 - Object Serialization and the .NET Remoting Layer

{

Chapter 13 - Building a Better Window (Introducing Windows Forms) public static int Main(string[] args)

Chapter 14 - A Better Painting Framework (GDI+)

{

Console.WriteLine("Rusty is less than Chucky!");

else

Console.WriteLine("Chucky is less than Rusty!"); return 0;

}

}

Assuming you have a Car type that implements IComparable, overloading the comparison operators is trivial. Here is the updated class definition:

// This class is also comparable using the comparison operators.

public class Car : IComparable

{

...

public int CompareTo(object o)

C# and the .NET Platform, Second Edition

{

Thisreturncomp ehensive text starts with a brief overview of the

1;

C# language and then quickly moves to key technical and if(this.CarID < temp.CarID)

architectural issues for .NET developers. return -1;

else

return 0;

Table of Contents

}

C# and the .NET Platform, Second Edition

public static bool operator < (Car c1, Car c2)

Introduction

{

Part One - Introducing C# and the .NET Platform

IComparable itfComp = (IComparable)c1;

Chapter 1 - The Philosophy of .NET

return (itfComp.CompareTo(c2) < 0);

Chapter 2 - Building C# Applications

}

Part Two - The C# Programming Language

public static bool operator > (Car c1, Car c2)

Chapter 3 - C# Language Fundamentals

{

Chapter 4 - Object-Oriented Programming with C#

IComparable itfComp = (IComparable)c1;

Chapter 5 - Exceptions and Object Lifetime

return (itfComp.CompareTo(c2) > 0);

Chapter 6 - Interfaces and Collections

}

Chapter public7 - CallbackstaticInterfaces,boolDelegates,operatorand<=Events(Car c1, Car c2)

Chapter {8 - Advanced C# Type Construction Techniques

Part Three - PrograIComparableming with .NETitfCompAssemblies= (IComparable)c1;

Chapter 9 - Understandingreturn (itfComp.NET Assemblies.CompareTo(c2) <= 0);

}

Chapter 10 - Processes, AppDomains, Contexts, and Threads

public static bool operator >= (Car c1, Car c2)

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

{

Part Four - Leveraging the .NET Libraries

IComparable itfComp = (IComparable)c1;

Chapter 12 - Object Serialization and the .NET Remoting Layer

return (itfComp.CompareTo(c2) >= 0);

Chapter 13 - Building a Better Window (Introducing Windows Forms)

}

Chapter 14 - A Better Painting Framework (GDI+)

}

Chapter 15 - Programming with Windows Forms Controls Chapter 16 - The System.IO Namespace

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

SOURCE The ObjCompWithOps project is located under the Chapter 8 subdirectory.

Chapter 18 - ASP.NET Web Pages and Web Controls

CODE

Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

Index

List of Figures

List of Tables

The InternalC#Representationand the .NET Platf rm,ofSecondOverloadedEdition Operators

Like any C# programming element, overloaded operators are represented using specific CIL instructions. To

Apress © 2003 (1200 pages)

begin examining what takes place behind the scenes, open up your OverLoadOps.exe assembly (created

This comprehensive text starts with a brief overview of the

previously) usingC#ildasmlanguage.exe. Asandyouthencanquicklysee frommovesFigureto key8-technical3, the +, and-, = =, and != operators are internally

expressed via hiddenarchitecturalmethods,issueswhichforin.NETthis developcase arersnamed. op_Addition(), op_Subtraction(), op_Equality(), and op_Inequality().

Table of Contents

C# and

Part

Chapter

Chapter

Part

Figure 8-3: Internal CIL representation of overloaded operators

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

Now, if you were to examine the specific CIL instructions for the op_Addition method, you would find that the

Chapter 13 - Building a Better Window (Introducing Windows Forms) specialname flag has also been inserted by csc.exe:

Chapter 14 - A Better Painting Framework (GDI+)

Chapter 15 - Programming with Windows Forms Controls

.method public hidebysig specialname static

Chapter 16 - The System.IO Namespace

valuetype OverLoadOps.Point op_Addition(valuetype OverLoadOps.Point p1,

Chapter 17 - Data Access with ADO.NET

valuetype OverLoadOps.Point p2) cil managed

Part Five - Web Applications and XML Web Services

{

Chapter 18 - ASP.NET Web Pages and Web Controls

...

Chapter 19 - ASP.NET Web Applications

}

Chapter 20 - XML Web Services

Index

ListTheoftruthFiguresof the matter is that any operator that you may overload equates to a specially named method in

Listtermsof Tablesof CIL. Table 8-3 documents the C#-operator-to-CIL mapping for the key C# operators.

Table 8-3: C#-Operator-to-CIL Special Name Roadmap

language demands. C# users can apply the + and – operators and/or call AddPoints()/SubtractPoints().

C# and the .NET Platform, Second Edition

Languages that cannot use overloaded operators (such as VB .NET) can make due with the public

by Andrew Troelsen ISBN:1590590554 member functions.

Apress © 2003 (1200 pages)

This comprehensive text starts with a brief overview of the

Triggering the "Special Names" from VB .NET

C# language and then quickly moves to key technical and

architectural issues for .NET developers.

On a related note, understand that it is also possible to directly call the specially named methods from operator-overload-lacking languages, given that they appear as public members on the type. Thus, if you

TablewereoftoContentsbundle the logic of the previous OverLoadOps project into a C# code library (named

OverLoadOpsCodeLibrary), a VB .NET client could interact with the + operator as follows:

C# and the .NET Platform, Second Edition

Introduction

PartImportsOne - IntroducingOverLoadOpsCodeLibraryC# and the .NET Platform

ChapterModule1 OverLoadedOpClient- The Philosophy of .NET

ChapterSub2 -Main()Bu lding C# Applications

Part Two - TheDimC#p1ProgrammingAs PointLanguage

p1.x = 200

Chapter 3 - C# Language Fundamentals

p1.y = 9

Chapter 4 - Object-Oriented Programming with C#

Dim p2 As Point

Chapter 5 - Exceptions and Object Lifetime

p2.x = 9

Chapter 6 - Interfaces and Collections

p2.y = 983

Chapter 7 - Callback Interfaces, Delegates, and Events

' Not as clean as calling AddPoints(),

Chapter 8 - Advanced C# Type Construction Techniques

' but it gets the job done.

Part Three - Programming with .NET Assemblies

Dim bigPoint = Point.op_Addition(p1, p2)

Chapter 9 - Understanding .NET Assemblies

Console.WriteLine("Big point is {0}", bigPoint)

Chapter 10 - Processes, AppDomains, Contexts, and Threads

End Sub

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

End Module

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

ChapterAs you13can- see,BuildingoverloadedBett r-Windowoperator(Introducing-challengedWindows.NET programmingForms) languages are able to directly invoke

Chapterthe internal14 - CILA Bettmethodsr Paintingas ifFrametheywereork (GDI+)"normal" methods. While it is not pretty, it works. Therefore, even Chapterif you (or15your- Programmingteammates)withdo Windowsnot take theFormstimeControlsto create a more friendly named method (such as

AddPoints()), the same functionality can be obtained using the underlying "special" methods.

Chapter 16 - The System.IO Namespace

Chapter 17 - Data Access with ADO.NET

SOURCE The OverLoadOpsCodeLibrary and VbNetOverLoadOpsClient projects are located

Part Five - Web Applications and XML Web Services

CODE under the Chapter 8 subdirectory.

Chapter 18 - ASP.NET Web Pages and Web Controls Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

Index

List of Figures

List of Tables

C# and the .NET Platform, Second Edition

Apress © 2003 (1200 pages)

This comprehensive text starts with a brief overview of the C# language and then quickly moves to key technical and architectural issues for .NET developers.

Table of Contents

C# and the .NET Platform, Second Edition

Introduction

Part One - Introducing C# and the .NET Platform

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

Part Two - The C# Programming Language

Chapter 3 - C# Language Fundamentals

Chapter 4 - Object-Oriented Programming with C#

Chapter 5 - Exceptions and Object Lifetime

Chapter 6 - Interfaces and Collections

Chapter 7 - Callback Interfaces, Delegates, and Events

Chapter 8 - Advanced C# Type Construction Techniques

Part Three - Programming with .NET Assemblies

Chapter 9 - Understanding .NET Assemblies

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Chapter 14 - A Better Painting Framework (GDI+)

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

Index

List of Figures

List of Tables

allows you to build custom conversion routines that allow your types to respond to the () operator.

C# and the .NET Platform, Second Edition

Therefore, if you configured the Square type correctly, you would be able to use the following syntax to

by Andrew Troelsen ISBN:1590590554 explicitly convert between types:

sq.sideLength = 3;

Rectangle rect = (Rectangle)sq;

Table of Contents

C# and the .NET Platform, Second Edition

Introduction

Part One - Introducing C# and the .NET Platform

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

Part Two - The C# Programming Language

Chapter 3 - C# Language Fundamentals

Chapter 4 - Object-Oriented Programming with C#

Chapter 5 - Exceptions and Object Lifetime

Chapter 6 - Interfaces and Collections

Chapter 7 - Callback Interfaces, Delegates, and Events

Chapter 8 - Advanced C# Type Construction Techniques

Part Three - Programming with .NET Assemblies

Chapter 9 - Understanding .NET Assemblies

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Chapter 14 - A Better Painting Framework (GDI+)

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

Index

List of Figures

List of Tables

Creating CustomC# and theConversion.NET Platform, SecRoutinesnd Edition

Now that you have a better feel about how it would look to interact with a type using a custom conversion

Apress © 2003 (1200 pages)

routine, let's see how to equip the type itself. C# provides two keywords ("explicit" and "implicit") that are

This comprehensive text starts with a brief overview of the

used to control howC# yourlanguagetypesandrespondthen quicklyduringmovesan attemptedto key techconversionical and. To begin, assume you have the following structurearchitecdefinitions:ural issues for .NET developers.

public struct Rectangle

Table of Contents

{

C# and the .NET Platform, Second Edition public int width, height;

Introduction

public void Draw()

Part One - Introducing C# and the .NET Platform

{ Console.WriteLine("Drawing a rect.");}

Chapter 1 - The Philosophy of .NET

// Rectangles can be explicitly converted

Chapter 2 - Building C# Applications

// into squares using the () syntax.

Part Two - The C# Programming Language

public static explicit operator Rectangle(Square s)

Chapter{3 - C# Language Fundamentals

Chapter 4 - Object-Oriented Programming with C#

Rectangle r;

Chapter 5 -rExc.heightptions and= sObject.sideLength;Lif time

Chapter 6 -rInterfaces.width and= s.CollectionssideLength;

Chapter 7 -returnCallback Interfaces,r; Delegates, and Events

Chapter}8 - Advanced C# Type Construction Techniques

public override string ToString()

Part Three - Programming with .NET Assemblies

Chapter{9 - Understanding .NET Assemblies

return string.Format("[Width = {0}; Height = {1}]",

Chapter 10 - Processes, AppDomains, Contexts, and Threads

width, height);

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

}

Part Four - Leveraging the .NET Libraries

}

Chapter 12 - Object Serialization and the .NET Remoting Layer

public struct Square

Chapter 13 - Building a Better Window (Introducing Windows Forms)

{

Chapter 14 - A Better Painting Framework (GDI+) public int sideLength;

Chapter 15 - Programming with Windows Forms Controls public void Draw()

Chapter 16 - The System.IO Namespace

{ Console.WriteLine("Drawing a square.");}

Chapter 17 - Data Access with ADO.NET

public override string ToString()

Part Five - Web Applications and XML Web Services

{

Chapter 18 - ASP.NET Web Pages and Web Controls

return string.Format("[SideLength = {0}]", sideLength);

Chapter}19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

}

Index

List of Figures

Notice that the Rectangle type defines an explicit conversion operator. Like the process of overloading an

List of Tables

operator, conversion routines make use of the C# operator keyword (in conjunction with the "explicit" or "implicit" keyword), and must be defined as static. The incoming parameter is the entity you are converting from while the return value is the entity you are converting to:

public static explicit operator Rectangle(Square s)

{...}

In any case, the assumption is that a square (being a geometric pattern in which all sides are of equal length) can be transformed into a rectangle, provided that the dimensions remain identical. Thus, you are free to convert a Square into a Rectangle in the following ways:

// Create a 10 * 10 square.

Square sq;

sq.sideLength = 3;

Console.WriteLine("sq = {0}", sq);

C# and the .NET Platform, Second Edition

// Convert Square to a new Rectangle.

This comprehensive text starts with a brief overview of the C# language and then quickly moves to key technical and architectural issues for .NET developers.

While it may not be all that helpful to convert your Square into a Rectangle within the same scope,

assume you have a function that has been prototyped to take Rectangle types. Using your explicit

Table of Contents

conversion operation, you can safely pass in Square types for processing:

C# and the .NET Platform, Second Edition

Introduction

private static void DrawThisRect(Rectangle r)

Part One - Introducing C# and the .NET Platform

{r.Draw();}

Chapter 1 - The Philosophy of .NET

...

Chapter 2 - Building C# Applications

// Meanwhile, back in Main()...

Part Two - The C# Programming Language

DrawThisRect((Rectangle)sq);

Chapter 3 - C# Language Fundamentals

Chapter 4 - Object-Oriented Programming with C#

Chapter 5 - Exceptions and Object Lifetime

Explicit Conversion Operators for the Square Type

Chapter 6 - Interfaces and Collections

Chapter 7 - Callback Interfaces, Delegates, and Events

Now that you can explicitly convert squares into rectangles, let's update the Square structure to support a

Chapter 8 - Advanced C# Type Construction Techniques

few conversions of its own. Given that a square is symmetrical on each side, it might be helpful to provide

Part Three - Programming with .NET Assemblies

an explicit conversion routine that allows the caller to cast from a System.Int32 type into a Square (which,

Chapter 9 - Understanding .NET Assemblies

of course, will have a side length equal to the incoming integer). Likewise, what if you were to update

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Square such that the caller can cast from a Square into a System.Int32? Here is the calling logic:

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Part Four - Leveraging the .NET Libraries

// Converting System.Int32 to Square.

Chapter 12 - Object Serialization and the .NET Remoting Layer

Square sq2 = (Square)90;

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Console.WriteLine("sq2 = {0}", sq2);

Chapter 14 - A Better Painting Framework (GDI+)

// Convert a Square to a System.Int32.

Chapter 15 - Programming with Windows Forms Controls int side = (int)sq2;

Chapter 16 - The System.IO Namespace

Console.WriteLine("Side of sq2 = {0}", side);

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

And here is the update to the Square type:

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

Chapterpublic20struct- XML WebSquareServices

{

Index

public int sideLength;

List of Figures

public void Draw()

List of Tables

{ Console.WriteLine("Drawing a square.");} public override string ToString()

{

return string.Format("[SideLength = {0}]", sideLength);

}

public static explicit operator Square(int sideLength)

{

Square newSq;

newSq.sideLength = sideLength; return newSq;

}

public static explicit operator int (Square s) {return s.sideLength; }

}

Wild, huh? To be honest, the need to convert from a Square into a System.Int32 may not be the most

conversion routines: The compiler does not care what you convert to or from, as long as you have written

Apress © 2003 (1200 pages)

syntactically correct code. Thus, as with overloading operators, just because you can create an explicit

This comprehensive text starts with a brief overview of the

cast operation for a given type does not mean you should. Typically this technique will be most helpful

C# language and then quickly moves to key technical and

when creating .NET structure types, given that they are unable to participate in classical inheritance architectural issues for .NET developers.

(where casting comes for free).

Table of Contents

C# and the .NET Platform, Second Edition

Introduction

Part One - Introducing C# and the .NET Platform

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

Part Two - The C# Programming Language

Chapter 3 - C# Language Fundamentals

Chapter 4 - Object-Oriented Programming with C#

Chapter 5 - Exceptions and Object Lifetime

Chapter 6 - Interfaces and Collections

Chapter 7 - Callback Interfaces, Delegates, and Events

Chapter 8 - Advanced C# Type Construction Techniques

Part Three - Programming with .NET Assemblies

Chapter 9 - Understanding .NET Assemblies

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Chapter 14 - A Better Painting Framework (GDI+)

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

Index

List of Figures

List of Tables

Defining ImplicitC# and theConversion.NET Platf rm,RoutinesSecond Edition

Thus far, you have equipped your Rectangle type to honor explicit conversions between Square types.

Apress © 2003 (1200 pages)

However, what about the following implicit conversion?

This comprehensive text starts with a brief overview of the

C# language and then quickly moves to key technical and

architectural issues for .NET developers.

// Attempt to make an implicit cast.

Square s3;

s3.sideLength= 83;

Table of Contents

Rectangle rect2 = s3;

C# and the .NET Platform, Second Edition

Introduction

PartAs youOnemight- Introducingexpect, C#thisandcodethewill.NETnotPlatformcompile, given that you have not provided an implicit conversion Chapterroutine1for-theTheRectanglePhilosophytypeof ..NETNow here is the catch: It is illegal to define explicit and implicit conversion

Chapterfunctions2 on- Buildingthe sameC#type,A plicationsif they do not differ by their return type or parameter set. This might seem like

Partlimitation;Two - Thehowever,C# Programmingthe secondLanguagecatch is that when a type defines an implicit conversion routine, it is legal

Chapterfor the 3caller- C#toLanguagemake useFundamof the explicitntals cast syntax!

Chapter 4 - Object-Oriented Programming with C#

Confused? To clear things up, let's begin by modifying the existing conversion routine for the Rectangle to

Chapter 5 - Exceptions and Object Lifetime

make use of the C# "implicit" keyword:

Chapter 6 - Interfaces and Collections

Chapter 7 - Callback Interfaces, Delegates, and Events

public static implicit operator Rectangle(Square s)

Chapter 8 - Advanced C# Type Construction Techniques

{

Part Three - Programming with .NET Assemblies

Rectangle r;

Chapter 9 - Understanding .NET Assemblies

r.height = s.sideLength;

Chapter 10 - Processes, AppDomains, Contexts, and Threads r.width = s.sideLength;

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming return r;

Part Four - Leveraging the .NET Libraries

}

Chapter 12 - Object Serialization and the .NET Remoting Layer Chapter 13 - Building a Better Window (Introducing Windows Forms)

ChapterWith this14update,- A B tteryouPareintinowg Frablem wtorkconvert(GDI+)between types as follows:

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

// Implicit cast OK!

Chapter 17 - Data Access with ADO.NET

Square s3;

Part Five - Web Applications and XML Web Services

s3.sideLength= 83;

Chapter 18 - ASP.NET Web Pages and Web Controls

Rectangle rect2 = s3;

ChapterConsole19.-WriteLine("rect2ASP.NET b Applications= {0}", rect2);

ChapterDrawThisRect(s3);20 - XML Web Services

Index// Explicit cast syntax still OK!

Square s4;

List of Figures

s4.sideLength = 3;

List of Tables

Rectangle rect3 = (Rectangle)s4;

Console.WriteLine("rect3 = {0}", rect3);

Do be aware that it is permissible to define explicit and implicit conversion routines for the same type as long as their signatures differ. Thus, you would update the Square as follows:

public struct Square

{

//Can call as:

//Square sq2 = (Square)90;

//or as:

//Square sq2 = 90;

public static implicit operator Square(int sideLength)

{

Square newSq;

C# and the .NET Platform, Second Edition newSq.sideLength = sideLength;

}Apress © 2003 (1200 pages)

This comprehensive text starts with a brief overview of the

//Must call as:

C# language and then quickly moves to key technical and

// int side = (Square)mySquare; architectural issues for .NET developers.

public static explicit operator int (Square s)

{ return s.sideLength; }

}

Table of Contents

C# and the .NET Platform, Second Edition

Introduction

Part One - Introducing C# and the .NET Platform

SOURCE The UserDefinedConversions project is located under the Chapter 8 subdirectory.

Chapter 1 - The Philosophy of .NET

CODE

Chapter 2 - Building C# Applications

Part Two - The C# Programming Language

Chapter 3 - C# Language Fundamentals

Chapter 4 - Object-Oriented Programming with C#

Chapter 5 - Exceptions and Object Lifetime

Chapter 6 - Interfaces and Collections

Chapter 7 - Callback Interfaces, Delegates, and Events

Chapter 8 - Advanced C# Type Construction Techniques

Part Three - Programming with .NET Assemblies

Chapter 9 - Understanding .NET Assemblies

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Chapter 14 - A Better Painting Framework (GDI+)

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

Index

List of Figures

List of Tables

The InternalC#Representationand the .NET Platf rm,ofSecondCustomEditionConversion Routines

Before moving on, you have one more conversion detail to contend with. Like overloaded operators,

Apress © 2003 (1200 pages)

methods that are qualified with the "implicit" or "explicit" keywords have "special" names in terms of CIL:

This comprehensive text starts with a brief overview of the op_implicit and opC#_explicit,languagerespectivelyand then quickly(Figuremoves8-4). to key technical and

architectural issues for .NET developers.

Table

C# and

Part

Chapter

Chapter

Part

Chapter

Chapter

Chapter

Figure 8-4: CIL representation of user-defined conversion routines

Chapter 7 - Callback Interfaces, Delegates, and Events

Chapter 8 - Advanced C# Type Construction Techniques

PartAs youThreemight- Programmingimagine, youwithcannot.NET guaranteeAssembli sthat a given .NET language will be able to interact with a Chaptertype's set9 of- Understandicustom conversiong .NET Assembliesfunctions, given that the () cast operator is a C#-ism. However, you would

Chapterstill be 10able- toProcesses,interact withAppDomains,these membersContexts,usinga d theirThreadsunderlying CIL representation:

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Part Four - Leveraging the .NET Libraries

Module UserConvApp

Chapter 12 - Object Serialization and the .NET Remoting Layer

Sub Main()

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Dim s As Square

Chapter 14 - A sBetter.sideLengthPainting Framework= 83 (GDI+)

Chapter 15 - ProgrammingDim rect withAs WindowsRectangleForms=ControlsRectangle.op_Implicit(s)

Chapter 16 - TheConsoleSy tem..IOWriteLine("rectNamespace = {0}", rect)

End Sub

Chapter 17 - Data Access with ADO.NET

End Module

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

That wraps up our examination of defining custom conversion routines (and this chapter). Remember that

Chapter 20 - XML Web Services

this bit of syntax is simply a shorthand notation for "normal" member functions, and in this light is always

Index optional.

List of Figures

List ofSOURCETables The UserConvLib and VbNetUserConvClient projects are located under the Chapter 8

CODE subdirectory.