[fpc-devel] Question on constref

[Ondrej Pokorny]

On 02.02.2023 11:00, Michael Van Canneyt via fpc-devel wrote:
> In userspace, the best seems
>
> Function FreeAndNil<T :TObject>(Obj : T) : T;
>
> begin
>   Obj.Free;
>   Result:=Nil;
> end;
>
> With automatic type inference for generics, this allows you to do
>
> A:=FreeAndNil(A);

Michael, bringing your idea to the next step, FPC can do it !!!

program test;

{$mode objfpc}{$h+}
{$modeswitch ImplicitFunctionSpecialization}

generic procedure FreeAndNil<T: TObject>(var Obj: T);
var
   Temp: TObject;
begin
   Temp := Obj;
   Obj := nil;
   Temp.Free;
end;

type
   TSomeObject = class(TObject);

var
   X: TSomeObject;
begin
   X := TSomeObject.Create;
   FreeAndNil(X);
   if Assigned(X) then
     Writeln('assigned')
   else
     Writeln('nil');
   ReadLn;
end.

-----

Delphi cannot do it. FPC rocks!

The only disadvantage is that you get a FreeAndNil copy for every type 
you pass into the parameter (?)

Do we want to change it in SysUtils? :)

Ondrej