CODEWITHSUNDEEP
delphidelphi-xe7
ThisGuy
ThisGuy

Reputation: 1415

Array of Colors

I am trying to work with an array of colors that is a constant. But Delphi keeps giving me compiling errors. I can't seem to figure out what I'm doing wrong... 

const
  Statuses : array[0..3] of TAlphaColors =
                            (
                              TAlphaColors.Lightgray, //error here: says insert a '(', even though I already have one
                              TAlphaColors.Yellow,
                              TAlphaColors.Limegreen,
                              TAlphaColors.Blue
                             );

Upvotes: 2

Views: 3227

Answers (1)

David Heffernan
David Heffernan

Reputation: 612824

The problem you face is that TAlphaColor.Lightgray, and indeed all the other TAlphaColor.XXX that you name are ordinal true constant. Whereas TAlphaColors is a record type.

Let's take a look at the relevant definitions:

type
  TAlphaColor = type Cardinal;

  TAlphaColorRec = record
  const
    Alpha = TAlphaColor($FF000000);
    Aliceblue = Alpha or TAlphaColor($F0F8FF);
    Antiquewhite = Alpha or TAlphaColor($FAEBD7);
    .... many more color constant omitted
    constructor Create(const Color: TAlphaColor);
    class var ColorToRGB: function (Color: TAlphaColor): Longint;
    case LongWord of
      0:
        (Color: TAlphaColor);
      2:
        (HiWord, LoWord: Word);
      3:
{$IFDEF BIGENDIAN}
        (A, R, G, B: System.Byte);
{$ELSE}
        (B, G, R, A: System.Byte);
{$ENDIF}
  end;

So the constants are not of type TAlphaColorRec. Indeed it's one of the great frustrations of the language that you cannot declare nested constants in a record that are of that record type. These constants are ordinal true constants.

Note that the record itself has data in a variant part of the record. And the field of interest is the Color field. So, you could declare your constant array like so:

const
  Statuses : array[0..3] of TAlphaColors = (
    (Color: TAlphaColors.Lightgray),
    (Color: TAlphaColors.Yellow),
    (Color: TAlphaColors.Limegreen),
    (Color: TAlphaColors.Blue)
  );

If only Embarcadero had had the foresight to allow us to write code like this:

type
  TMyRecord = record
  public
    const
      MyConst: TMyRecord = ();
  end;

Upvotes: 3

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