generics - Delphi XE8 bug in TList<T>, need workaround

Question

After upgrading to XE8 some of our projects start to break data. Looks like a bug in TList realization.

program XE8Bug1;
{$APPTYPE CONSOLE}

uses
  System.SysUtils, Generics.Collections;

type
  TRecord = record
    A: Integer;
    B: Int64;
  end;

var
  FRecord: TRecord;
  FList: TList<TRecord>;

begin
  FList := TList<TRecord>.Create;
  FRecord.A := 1;
  FList.Insert(0, FRecord);
  FRecord.A := 3;
  FList.Insert(1, FRecord);
  FRecord.A := 2;
  FList.Insert(1, FRecord);
  Writeln(IntToStr(FList[0].A) + IntToStr(FList[1].A) + IntToStr(FList[2].A));

end.

This code prints "123" in XE7 and before (as it should be), but in XE8 it prints "120". Maybe someone know a quickfix for this?

Update: unofficial fix is here

question from:https://stackoverflow.com/questions/29906723/delphi-xe8-bug-in-tlistt-need-workaround

Answer 1

I found that now the TList<T>.Insert method call TListHelper.InternalInsertX depends on the data size, in my case:

procedure TListHelper.InternalInsertN(AIndex: Integer; const Value);
var
  ElemSize: Integer;
begin
  CheckInsertRange(AIndex);

  InternalGrowCheck(FCount + 1);
  ElemSize := ElSize;
  if AIndex <> FCount then
    Move(PByte(FItems^)[AIndex * ElemSize], PByte(FItems^)[(AIndex * ElemSize) + 1], (FCount - AIndex) * ElemSize);
  Move(Value, PByte(FItems^)[AIndex * ElemSize], ElemSize);
  Inc(FCount);
  FNotify(Value, cnAdded);
end;

I see the problem in the first Move call. Destination should be:

PByte(FItems^)[(AIndex + 1) * ElemSize]

not

PByte(FItems^)[(AIndex * ElemSize) + 1]

Aaargh!

Finally, I've used the System.Generics.Defaults.pas and System.Generics.Collections.pas units from Delphi XE7 in my projects, and now all works as expected.

Update: as I see, RTL not affected, as it isn't use TList<T>.Insert for T with SizeOf > 8 (or maybe I miss something?)