Question

Hello i get error E2197: [DCC Error] proj1.pas(34): E2197 Constant object cannot be passed as var parameter:

unit proj1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, AdvEdit;

type
  TForm1 = class(TForm)
    AdvEdit1: TAdvEdit;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure SetEditText(const instr: string; out outstr: string);
begin
  outstr := instr;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  SetEditText('Pippo', AdvEdit1.Text);
end;

end.

Of course, i can solve writing:

procedure TForm1.Button1Click(Sender: TObject);
var sText: string
begin
  SetEditText('Pippo', sText);
  AdvEdit1.Text := sText;
end;

But when i have many AdvEdit, then it is hard. Then i ask, is possible solve the problem in some mode giving directly TAdvEdit.Text as parameter in mine procedure?
Thanks very much.

Answer 1

I presume that Text is a property. And you cannot pass a property to a var or out parameter. You can only pass variables to parameters of those kinds.

You’ll need to find a different way to write your code. You’ve come up with one such idea, but it seems needlessly complex to me. I cannot see anything simpler than:

AdvEdit1.Text := 'Pippo';

How could there be any code simpler than this? You need to specify at a bare minimum the following:

• The target control.
• That we are dealing with the Text property.
• The fact that we are assigning.
• The new value.

The code above does that and nothing more.