[out] and [in] in records

[efortier 0]

Hi all,

 

I'm trying to find what is the meaning of those and what the compiler does with variables declared with with either [out] or [in], like these:

TMyRecord = record
  [in] SrcPosition: TPoint;
  [out] DstPosition: TPoint;
end;

I've been trying to search on google and in the doc, but all I can find is references to the normal in and out keywords.

 

Thanks!

[David Heffernan 2345]

Where are the attributes defined? 

[Lars Fosdal 1792]

VCL.Forms, VCL.Printers and VCL.StdCtrls has a few of these, but for only for function parameters in CLR code.

{$IF DEFINED(CLR)}
type
  TMonitorEnumerator = class
    FList: TList;
    FEnumProc: TMonitorEnumProc; // reference to the delegate so the garbage collector doesnt free it
    constructor Create(List: TLIst);
    function EnumMonitorsProc(hm: HMONITOR; dc: HDC;
      [in] var r: TRect; Data: LPARAM): Boolean;
  end;
{$ENDIF}

and on the topic of CLR: https://stackoverflow.com/questions/2210122/why-are-there-so-many-if-definedclr-in-the-vcl-rtl

Yeah... that stuff really should be made to go away. 

 

[Uwe Raabe 2057]

Indeed ,NET has something called InAttribute and OutAttribute. AFAIK, there is no corresponding thing in Delphi.

[Remy Lebeau 1393]

On 8/19/2019 at 2:17 AM, Lars Fosdal said:

VCL.Forms, VCL.Printers and VCL.StdCtrls has a few of these, but for only for function parameters in CLR code.

Right, such examples are using [in] and [out] only for function parameters, not for record fields like in efortier's example.  I've never seen such attributes used on fields.

[Микола Петрівський 10]

In modern Delphi you can do that like this:

TMyRecord = record
private
  FSrcPosition: TPoint;
  function GetDestination: TPoint;
public
  property SrcPosition: TPoint write FSrcPosition;
  property DstPosition: TPoint read GetDestination;
end;