Chapter 9 - Structures and Enumerations

Structures and Enumerations 1C# 30

C# 3.0C# 3.0

Chapter 9 Structures and EnumerationsEnumerations

Copyright SELA Software & Education Labs Ltd. 14-18 Baruch Hirsch St. Bnei Brak 51202 Israel

IntroductionStructures and Enumerations 2C# 30

Introduction Classes are good but we need more Classes are good, but we need more

types! Structures a limited, yet more efficient version of

classes Enumerations

These types are value-type user defined typestypes Delegates and interfaces (two new reference type types)

will be discussed laterwill be discussed later



SStructures


C# StructuresStructures and Enumerations 4C# 30

C# StructuresClasses might sometimes be too hea Classes might sometimes be too heavy Reference type variables and their manipulation

involves a lot of overhead

Structures (defined using the structkeyword) are value-type user defined typestypes They are derived from System.ValueType Are allocated and directly manipulated on the stack

(unless boxing is required)


A Structure Example: PointStructures and Enumerations 5C# 30

A Structure Example: Pointstruct Point{{

publicPoint(int x,int y){_x=x;y=y;_y y;

}publicint X{

get{return x;}get{return_x;}set{_x=value;}

}bli i t Y{publicint Y{get{return_y;}set{_y=value;}

}publicoverridestringToString(){

return"("+ x+","+ y+")";( _ , _y ) ;}privateint _x;privateint y;


privateint _y;}

A Structure Example: PointStructures and Enumerations 6C# 30

A Structure Example: Point

Structures can declare fields, methods, propertiesproperties

Structures can define constructors and can override virtual methods derived fromcan override virtual methods derived from System.ValueType


Structure LimitationsStructures and Enumerations 7C# 30

Structure Limitations Cannot be part of an inheritance tree: Cannot be part of an inheritance tree:

They cannot inherit from other classes They are implicitly sealed Virtual methods and protected members are irrelevant

f t tfor structures Cannot have a null value

Only references can be pointing to null

Cannot have a parameterless constructor Cannot have a parameterless constructor For performance reasons, it is not always called

Cannot have a finalizer Value types are not garbage collected (unless boxed)


yp g g ( )

Design GuidelinesStructures and Enumerations 8C# 30

Design GuidelinesStr ct res sho ld be sed for light eight Structures should be used for light-weight objects with value semanticsj Point, Complex number, the Systems decimal and DateTime types, etc.ate e types, etc

Users expect them to behave as primitive value-typesvalue-types Value semantics for equality, assignment, comparison No significant side effects


Structure Usage ExampleStructures and Enumerations 9C# 30

Structure Usage ExamplestaticvoidMain(){() {

Pointp=newPoint(0,0);Console.WriteLine(p);p.X =5;p.X 5;p.Y =10;Console.WriteLine(p);int i =p X;int i =p.X;i =p.Y;

}

Structure instances must be created using the new operatorthe new operator Or, you must initialize every field before using them


Fields Initialization NotesStructures and Enumerations 10C# 30

Fields Initialization Notes For a class: For a class:

You can define any constructor, including a parameter less oneparameter-less one

Fields that are not initialized in the constructor, automatically get a default value at run timeautomatically get a default value at run time

For a structure: You cannot define a parameter-less constructor All fields should be initialized in the constructors:

The default provided parameter-less constructor assigns all fields with their default valuesTh il k th t ll d fi d t t The compiler makes sure that all user-defined constructors provide all fields with initial values



N ll bl TNullable Types


The Need for Nullable TypesStructures and Enumerations 12C# 30

The Need for Nullable TypesReference types can have an value: n ll Reference types can have an value: null

Sometimes it is necessary to mark aSometimes it is necessary to mark a Value type as nullor undefined A Boolean field in a database can store the values

true or false, or it may contain neither

NET 2 0 introd ces N llable T pes .NET 2.0 introduces Nullable Types C# 2.0 introduces convenient syntaxC# 2.0 introduces convenient syntax


Nullable TypeStructures and Enumerations 13C# 30

Nullable TypeN llable t pes can represent the al es Nullable types can represent the values of an underlying value type, and an y g ypadditional null valueTh N ll bl T t t The Nullable type exposes two public properties:p p p HasValue Set to true when the variable contains a

non-null valuenon null value ValueIf HasValue is true, Valuecontains a

meaningful value Otherwise it throws anmeaningful value. Otherwise, it throws an InvalidOperationException


Using NullableStructures and Enumerations 14C# 30

Using Nullable//Nullable Integerver 1 0//Nullable Integerver 1.0NullablenInt =newNullable(5);nInt =nInt +5;

l i i ( )Console.WriteLine(nInt);...nInt =null;;if(nInt ==null){

......}if(nInt.HasValue){{

...}


Nullable ? ShorthandStructures and Enumerations 15C# 30

Nullable ? Shorthand//Nullable Integerver 2 0//Nullable Integerver 2.0int?nInt =5; //int?isNullablenInt =nInt +5;

l i i ( )Console.WriteLine(nInt);...nInt =null;;int?kInt =null;if(nInt ==kInt){{

...}


GetValueOrDefault ??Structures and Enumerations 16C# 30

GetValueOrDefault ??The GetVal eOrDefa lt method ret rns The GetValueOrDefault method returns the nullables value or the specified pdefault:publicTGetValueOrDefault(TdefaultValue);

C# offers a short-hand for this method:

publicTGetValueOrDefault(TdefaultValue);

C# offers a short-hand for this method:int?x=null;int y=x??21;//y==21x=42;y=x??21;//y==42y x??21;//y 42


Nullables SummaryStructures and Enumerations 17C# 30

Nullables SummaryN llable t pes are sed to create al e Nullable types are used to create value types that can contain null as a valueyp The syntax T? is shorthand for System.Nullable The HasValue property returns true if the variable The HasValue property returns true if the variable

contains a value, or false if it is nullThe Value property returns a value if one is assigned The Value property returns a value if one is assigned, or throws an exceptionTh d f lt l f ll bl t i bl t The default value for a nullable type variable sets HasValue to false. The Value is undefined

This is a valid C# statement:int x=y>z?a??10:b??20;


int x y>z?a??10:b??20;


E iEnumerations


Enumerations IntroductionStructures and Enumerations 19C# 30

Enumerations IntroductionThe en meration concept in C# is similar The enumeration concept in C# is similar to the C/C++ enumerated type:yp Defining a set of symbolic names and integral values

Using enums is recommended: Using enums is recommended: Improves readability and maintainability Improves type safety

NET enums are first class citizens in the .NET enums are first-class citizens in the type system Enums derive from System.Enum, which derives from System.ValueType


Enum DefinitionStructures and Enumerations 20C# 30

Enum DefinitionenumFruit{

Apple,Banana,Banana,Orange

}//Dontprefixenumvalueswiththeenumname

The default underlying type of an enumerator type is int but it can beenumerator type is int, but it can be defined to be any other integral typeenumFruit:byte //Thisdoesntmeanderives{

Apple Apple,Banana,Orange


}

Manipulating Enum ObjectsStructures and Enumerations 21C# 30

Manipulating Enum Objects//Gettingallenum'snames//Gettingallenum snamesstring[]fruits=Enum.GetNames(typeof(Fruit));

// f l t di l ll ibl ti//Usefultodisplayallpossibleenumoptionsforeach(stringfruitNameinfruits)

Console.WriteLine(fruiteName);( )

Console.WriteLine("Enteryourfavoritefruit:");try{try{

strings=Console.ReadLine();//ConvertingasymbolintoanenuminstanceFruitf=(Fruit)Enum Parse(typeof(Fruit) s);Fruitf=(Fruit)Enum.Parse(typeof(Fruit),s);

}catch(ArgumentException){

C l W it Li ("S i lidf it")Console.WriteLine("Sorry,aninvalidfruit");}


Manipulating Enum ObjectsStructures and Enumerations 22C# 30

Manipulating Enum Objects//Checkingifavalueisdefinedforanenum//Checkingifavalueisdefinedforanenumif(!Enum.IsDefined(typeof(Fruit),5))

Console.WriteLine(5isnotdefined");

//Gettingtheenumeratedtypeunderlyingtype.Console.WriteLine("TheunderlyingtypeofFruit:"+

Enum.GetUnderlyingType(typeof(Fruit)));}


Bit Flag TypesStructures and Enumerations 23C# 30

Bit Flag Types Enumerated types can also be used to Enumerated types can also be used to

define bit flag types A bit flag enum can have multiple flags on and off

A numeric value must be explicitlyA numeric value must be explicitly assigned to each symbol:[Fl ][Flags]enum Characteristics{

Smart =0x0001, //Bit0setCalm =0x0002, //Bit1setTall =0x0004, //Bit2set, //Kind =0x0008, //Bit3setGentle =0x0010, //Bit4setGorgeous =0x001F //Allbitsset


Gorgeous =0x001F //Allbitsset}

Bit Flag Type Usage ExampleStructures and Enumerations 24C# 30

Bit Flag Type Usage ExampleclassPersonclassPerson{

publicPerson(stringname,Characteristicscharacter){{

_name=name;_character=character;

}}publicvoidSet(Characteristicscharacter){

_character|= character;}publicoverridestringToString()pub c o e de st g oSt g(){

return_name+"is:"+_character;}}privatestring_name;privateCharacteristics_character;

}


}

Bit Flag Type Usage ExampleStructures and Enumerations 25C# 30

Bit Flag Type Usage ExamplestaticvoidMain(){staticvoidMain(){

Personjerry=newPerson("Jerry",Characteristics.Tall |Characteristics.Kind);

C l W it Li (j )Console.WriteLine(jerry);

jerry.Set(Characteristics.Gentle |Characteristics.Calm |Characteristics.Smart);

Console.WriteLine(jerry);}}

And the output is: Jerry is: Tall, KindJerry is: Gorgeous


Bit Flags String FormattingStructures and Enumerations 26C# 30

Bit Flags String FormattingEn m ToString() provided a comma Enum.ToString() provided a comma-separated list of set flagsp g

There are two ways to get this behavior:1 Decorate the enum with the [Flags] attribute1. Decorate the enum with the [Flags] attribute2. Call the ToString() method on with an additional

formater parameter Fformater parameter F


Chapter SummaryStructures and Enumerations 27C# 30

Chapter SummaryUser defined al e t pes User-defined value types Structs are:

Derived from System.ValueType and sealed Have a pre-defined non-overridable parameterless ctor Can override Objects methods Can not be null (use Nullable)

Enums are: Similar to C++ enums Define a scope for their constants values Have methods to show & parse strings May be marked with [Flags]


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Chapter 9 - Structures and Enumerations