cascaded record constants
lazarus / 62-General

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lt.col.blair · 2014-10-24 17:33

Hi,

Is it possible to define constants that are made up of records which
again contain records?

My structures are like this:
Code: [Select]RDartPolar = record
  Radius: NRadius;
  Field: NField;
end;

RBoardPosition = record
  BoardPos: RPolar;
  RectPos: TPoint;
end;

const
  PolarNULL: RDartPolar=(Radius: radMissed; Field: fld20);
  PointNULL: TPoint = (X: -1000; Y: -1000);
  DartNULL: RBoardPosition=(BoardPos: PolarNULL; RectPos: PointNULL);
//raises compiler error '"(" expected but identifier PolarNULL found.'

Is this an illegal construction or do I have some other error in my
code?

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Blaazen · 2014-10-24 21:12

Isn't it type mismatch? RBoardPosition.BoardPos is type RPolar while
PolarNULL is type RDartPolar.

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lt.col.blair · 2014-10-25 12:22

Sorry, that was a typo in my post - happens, when you copy paste one
part and type the other...
In my original code the BoardPos is also defined as RDartPolar.

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User137 · 2014-10-25 13:31

Well, i tried at least. Suspecting compiler just won't allow it? I
went a bit further but it's giving me a vague "illegal expression",
putting cursor ^ here:
(BoardPos: (Radius: PolarNULL.Radius^; Field: PolarNULL.Field);

Code: [Select]  NRadius = single;
  NField = string;

  RDartPolar = record
    Radius: NRadius;
    Field: NField;
  end;

  RBoardPosition = record
    BoardPos: RDartPolar;
    RectPos: TPoint;
  end;

const
  radMissed = 1;
  fld20 = '20';
  PolarNULL: RDartPolar = (Radius: radMissed; Field: fld20);
  PointNULL: TPoint = (X: -1000; Y: -1000);

  //DartNULL: RBoardPosition = (BoardPos: PolarNULL; RectPos:
PointNULL);
  DartNULL: RBoardPosition =
    (BoardPos: (Radius: PolarNULL.Radius; Field: PolarNULL.Field);
     RectPos: (x: PointNULL.x; y: PointNULL.y));

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taazz · 2014-10-25 13:36

It has to do with writable constants that FPC supports. Although the
default is not writable the compiler will not allow to use record
constants as values for other record constants.

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marcov · 2014-10-26 09:27

Probably the reason that the compiler does this is because of
equality.

If a structured constant A could be added to a constant C (say as
field B)   then C.B<>A since they are located on a different address.