“Left side cannot be assigned to” for record type properties in Delphi

Question

I\'m curious to know why Delphi treats record type properties as read only:

  TRec = record
    A : integer;
    B : string;
  end;

  TForm1 = class(TForm)
         


        

Answer 1

A solution I frequently use is to declare the property as a pointer to the record.

type
  PRec = ^TRec;
  TRec = record
    A : integer;
    B : string;
  end;

  TForm1 = class(TForm)
  private
    FRec : TRec;

    function GetRec: PRec;
    procedure SetRec(Value: PRec);
  public
    property Rec : PRec read GetRec write SetRec; 
  end;

implementation

function TForm1.GetRec: PRec;
begin
  Result := @FRec;
end;  

procedure TForm1.SetRec(Value: PRec);
begin
  FRec := Value^;
end;

With this, directly assigning Form1.Rec.A := MyInteger will work, but also Form1.Rec := MyRec will work by copying all the values in MyRec to the FRec field as expected.

The only pitfall here is that when you wish to actually retrieve a copy of the record to work with, you will have to something like MyRec := Form1.Rec^