Chapter94:Structs

Section94.1:Declaringa struct

publicstructVector

{

publicintX;

publicintY;

publicintZ;

}

publicstructPoint

{

publicdecimalx,y;

publicPoint(decimalpointX,decimalpointY)

{

x=pointX;

y=pointY;

}

}

• structinstancefieldscanbesetviaaparametrizedconstructororindividuallyafterstructconstruction.
• Privatememberscanonlybeinitializedbytheconstructor.
• structdefines a sealed type that implicitly inherits from System.ValueType.
• Structs cannot inherit from any other type, but they can implement interfaces.
• Structsarecopiedonassignment,meaningalldataiscopiedtothenewinstanceandchangestooneofthem are not reflected by the other.
• Astructcannotbenull,althoughitcanusedasanullabletype:

Vectorv1=null;//illegal

Vector?v2=null;//OK

Nullable<Vector>v3=null//OK

• Structscanbeinstantiatedwithorwithoutusingthenewoperator.

//Bothoftheseareacceptable

Vectorv1=newVector();v1.X=1;

v1.Y=2;

v1.Z=3;

Vectorv2;

v2.X=1;

v2.Y=2;

v2.Z=3;

However,thenewoperatormust be usedin orderto usean initializer:

Vectorv1=newMyStruct{X=1,Y=2,Z=3};//OK

Vectorv2{X=1,Y=2,Z=3};//illegal

Astructcandeclareeverythingaclasscandeclare,withafewexceptions:

• Astructcannotdeclareaparameterlessconstructor.structinstancefieldscanbesetviaaparameterized constructororindividuallyafterstructconstruction.Privatememberscanonlybeinitializedbythe constructor.
• Astructcannotdeclaremembersasprotected,sinceitisimplicitlysealed.
• . Struct fields can only be initialized if they are const or static.

Section94.2:Structusage

Withconstructor:

Vectorv1=newVector();

v1.X=1;

v1.Y=2;

v1.Z=3;

Console.WriteLine(“X={0},Y={1},Z={2}”,v1.X,v1.Y,v1.Z);

//OutputX=1,Y=2,Z=3

Vectorv1=newVector();

//v1.Xisnotassigned

v1.Y=2;

v1.Z=3;

Console.WriteLine(“X={0},Y={1},Z={2}”,v1.X,v1.Y,v1.Z);

//OutputX=0,Y=2,Z=3

Pointpoint1=newPoint();

point1.x=0.5;

point1.y=0.6;

Pointpoint2=newPoint(0.5,0.6);

Withoutconstructor:

Vectorv1;

v1.Y=2;

v1.Z=3;

Console.WriteLine(“X={0},Y={1},Z={2}”,v1.X,v1.Y,v1.Z);

//OutputERROR“Useofpossiblyunassignedfield’X’

Vectorv1;

v1.X=1;

v1.Y=2;

v1.Z=3;

Console.WriteLine(“X={0},Y={1},Z={2}”,v1.X,v1.Y,v1.Z);

//OutputX=1,Y=2,Z=3

Pointpoint3;

point3.x=0.5;

point3.y=0.6;

If we use a struct with its constructor, we aren’t going to have problems with unassigned field (each unassigned field has null value).

Unlike classes, a struct doesn’t have to be constructed, i.e. there is no need to use the new keyword, unless you need to call one of the constructors. A struct does not require the new keyword because is a value-type and thus cannot be null.

Section94.3:Structsarecopiedonassignment

Sinse structs are value types all the data is copiedon assignment, and any modification to the new copy does not changethedatafortheoriginalcopy.Thecodesnippetbelowshowsthatp1iscopiedtop2andchangesmadeon p1does not affect p2instance.

varp1=newPoint{ x=1,

y=2

};

Console.WriteLine($”{p1.x}{p1.y}”);//12

varp2=p1;

Console.WriteLine($”{p2.x}{p2.y}”);//Sameoutput:12

p1.x=3;

Console.WriteLine($”{p1.x}{p1.y}”);//32

Console.WriteLine($”{p2.x}{p2.y}”);//p2remainthesame:12

Section94.4:Structimplementinginterface

publicinterfaceIShape

{

decimalArea();

}

publicstructRectangle:IShape

{

publicdecimalLength{get;set;}

publicdecimalWidth{get;set;}

publicdecimalArea()

{

returnLength*Width;

}

}