[fpc-devel] Copy/move operator

[Ben Grasset]

On Mon, Jun 17, 2019 at 5:57 PM Ryan Joseph <genericptr at gmail.com> wrote:

> The copy operator is always called on all assignments. Try actually
> running that and you’ll see. :)
>

Yeah, I noticed that afterwards once I checked. I'm not sure how much sense
that actually makes when the TList<T> is a function *result* as it is in
the static class function version of Create, though (i.e, you're not
assigning an existing TList<T> variable to another, you're returning a
brand new one.)

The version of Copy in my last comment was missing a SetLength, also, and
called `Move` incorrectly. Something like this is what I was going for:

program Test;

{$mode ObjFPC}
{$modeswitch AdvancedRecords}

type
  generic TList<T> = record
  public
    Data: array of T;
    class operator Copy(constref Src: TList; var Dest: TList); inline;
    class function Create(const Num: Integer): TList; static; inline;
  end;

  class operator TList.Copy(constref Src: TList; var Dest: TList);
  var Len: SizeInt;
  begin
    Len := Length(Src.Data);
    SetLength(Dest.Data, Len);
    Move(Src.Data[0], Dest.Data[0], SizeOf(T) * Len);
  end;

  class function TList.Create(const Num: Integer): TList;
  begin
    SetLength(Result.Data, Num);
  end;

begin
  // Do whatever here.
end.

Don't forget about your constant generics feature, also... can help in
avoiding "constructorish" things altogether quite a bit.
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