Dynamic arrays and copying

[Jacek Laskowski 57]

 

I create an array of arrays, then assign the data in whole rows (array).

 

Example code:

 

program Project1;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;

var
  lValues: array of TArray<Variant>;

procedure TestAddRowData();
var
  lRow : TArray<Variant>;
begin
  SetLength(lRow, 3);
  SetLength(lValues, 3);

  lRow[0] := 'one';
  lRow[1] := 1;
  lRow[2] := '1one';
  lValues[0] := lRow;

  lRow[0] := 'two';
  lRow[1] := 2;
  lRow[2] := '2two';
  lValues[1] := lRow;

  lRow[0] := 'three';
  lRow[1] := 3;
  lRow[2] := '3three';
  lValues[2] := lRow;
end;


begin
    TestAddRowData();
    Writeln(lValues[0, 0]);
    Writeln(lValues[0, 1]);
    Writeln(lValues[0, 2]);
    Writeln(lValues[1, 0]);
    Writeln(lValues[1, 1]);
    Writeln(lValues[1, 2]);
    Writeln(lValues[2, 0]);
    Writeln(lValues[2, 1]);
    Writeln(lValues[2, 2]);
    Readln;
end.

Results:

three
3
3three
three
3
3three
three
3
3three

 

I expected to get all the data according to their addition...

 

Isn't there a Copy on Write rule for arrays?

[Pawel Piotrowski 18]

The copy on write rule is only for strings.

Arrays are reference counted and that's it.

If you need to copy the content of the array, you need to use the copy() function. It will create a new instance of your array.

 

[David Heffernan 2290]

This issue is covered explicitly by the documentation: http://docwiki.embarcadero.com/RADStudio/Sydney/en/Structured_Types_(Delphi)#Dynamic_Arrays

[Stefan Glienke 1901]

procedure TestAddRowData();
begin
  lValues := [
    ['one', 1, '1one'],
    ['two', 2, '2two'],
    ['three', 3, '3three']
  ];

  // or
  SetLength(lValues, 3, 3);

  lValues[0,0] := 'one';
  lValues[0,1] := 1;
  lValues[0,2] := '1one';

  lValues[1,0] := 'two';
  lValues[1,1] := 2;
  lValues[1,2] := '2two';

  lValues[2,0] := 'three';
  lValues[2,1] := 3;
  lValues[2,2] := '3three';
end;