Usage of pascal variant record - pascal

Question

I need help from those who know the pascal very well.
I need (teachers requirement) to use a variant record. Those variant record are defined like this:
Temperature = record
case scale : TemperatureScale of
celsius : (celsius_value : ScaleCelsius);
kelvin : (kelvin_value : ScaleKelvin);
end;
According to primary sources I found during my research about this topic, I could not find how to use variant record, only how to declare it.
My primary sources: google search(found nothing), Case-Freepascal and Record-Freepascal
Edit for those who wonder what i must use in implementation it is exacly this:
type
UkPolozka = ^Polozka;
UkHodnota = ^Hodnota;
TypUdaj=(typretez, typcele, typrealne, typlogik, typpole, typobjekt);
VarZaznam = record
case Udaj: TypUdaj of
typretez: (retez: string);
typcele: (cele: word);
typrealne: (realne: single);
typlogik: (logik: boolean);
typpole: (pole: UkHodnota);
typobjekt: (objekt: UkPolozka);
end;
Polozka = record
Nazev: string;
Hodn: VarZaznam;
Dalsi: UkPolozka
end;
Hodnota = record
Hodn: VarZaznam;
Dalsi: UkHodnota
end;

Answer 1

Consider example record from Delphi Help. I modified it with tag.
Tag usage is optional and usually is not used and doesn't provide useful information.
Note that the first line outputs radius with the same value as height - they share the same memory.
Then I explicitly set tag (but fields stay the same)
Also note size difference for no-tag record and tagged one.
Note again - in most cases programmers don't define or use tag value. It might be unsafe to rely on tag (until you follow strict rules in assigning tags). I did not set rectangle tag, but program consider zero tag as the first variant.
Just assign needed field by name. Just read needed field by name. For your example varVarZaznam.retez:= 'test';
type
TShapeList = (Rectangle, Triangle, Circle, Ellipse, Other);
TFigure = record
case shape: TShapeList of
Rectangle: (Height, Width: Real);
Triangle: (Side1, Side2, Angle: Real);
Circle: (Radius: Real);
Ellipse, Other: ();
end;
TFigureNoTag = record
case TShapeList of
Rectangle: (Height, Width: Real);
Triangle: (Side1, Side2, Angle: Real);
Circle: (Radius: Real);
Ellipse, Other: ();
end;
var
Fig: TFigure;
begin
Fig.Height := 5;
Fig.Width := 3;
//default tag is zero = Rectangle
if Fig.shape = Rectangle then
Writeln('Rect ', Fig.Height:3:0, Fig.Width:3:0, Fig.Radius:3:0)
else
Writeln('not Rect');
Fig.shape := Circle;
if Fig.shape <> Rectangle then
Writeln('not Rect');
Writeln('Fig size ', SizeOf(TFigure), ' noTag size ', SizeOf(TFigureNoTag));
Readln;
output in Delphi:
Rect 5 3 5
not Rect
Fig size 32 noTag size 24