Problems with constructors

What is translated > Types > Records, Classes, Interfaces > Class > Constructors > Problems with constructors

Summarizing, there remain two problems for which the translated constructors have to be checked:

TCoordinate = class(TObject)

public

  constructor CreateRectangular(AX, AY: Double);

  constructor CreatePolar(Radius, Angle: Double);

private

  x,y : Double;  

end;

constructor TCoordinate.CreateRectangular(AX, AY: Double);

begin

  x := AX;

  y := AY;

end

constructor TCoordinate.CreatePolar(Radius, Angle: Double);

begin

  x := Radius * cos(Angle);

  y := Radius * sIn(Angle);

end

After translation the two constructors become ambiguous: 

__fastcall TCoordinate::TCoordinate( double AX, double AY )

 : x(AX),

   y(AY)

{

}

__fastcall TCoordinate::TCoordinate( double Radius, double Angle )

 : x(Radius * cos( Angle )),

   y(Radius * sin( Angle ))

{

}

They not only have the same signature now, but also the same name. In such cases the conflict has to be avoided manually. For example you can remove the second constructor and define a static function instead:

TCoordinate* __fastcall TCoordinate::CreatePolar( double Radius, double Angle )

{

  return new TCoordinate(Radius * cos( Angle ), Radius * sin( Angle )

}

At all positions, where the second constructor shall be used, the new function has to be used instead. This positions can be found easily, because Delphi2Cpp II inserts the original name of the constructor as a comment into the translated code, if the Verbose option is enabled and if the name is not written exactly as "Create".

P = /*CreatePolar*/ new TCoordinate( AX, AY );

->

P = TCoordinate::CreatePolar( AX, AY );

4. Calls of virtual constructors are allowed in Delphi, but in C++ such calls should be avoided in C++

As example the TPolygon class and the derived classes TTriangle and TSquare as defined here

http://www.delphibasics.co.uk/RTL.asp?Name=Abstract

can be taken:

  TPolygon = class

  ...

  protected

     procedure setArea; Virtual; Abstract;  // Cannot code until sides known

  ...

  TTriangle = class(TPolygon)

  protected

    procedure setArea; override;   // Override the abstract method

  TSquare = class(TPolygon)

  protected

    procedure setArea; override;   // Override the abstract method

constructor TPolygon.Create(sides, length : Integer);

begin

  ...

  setArea;

end;

In Delphi the setAres-procedure of the derived classes will be called in their constructors. With C++Builder this works well too, but other C++ compilers always try to call the setArea-procedure of TPolygon. Manual post-processing is necessary then. E.g. setArea could be made accessible and called after construction:

triangle = new TTriangle(3, 10);

triangle->setArea();

This page belongs to the DelphiXE2Cpp11 Documentation