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Report From: Delphi-BCB/RTL/Delphi/Other RTL [ Add a report in this area ]

Report #: 104609

Status: Reported

Stringlist assignment to itselft clears content

Project: Delphi

Build #: XE, XE2

Version: 16.4

Submitted By: Christian Holzner

Report Type: Minor failure / Design problem

Date Reported: 4/4/2012 1:24:49 AM

Severity: Infrequently encountered problem

Last Updated: 4/4/2012 11:26:31 PM

Platform: All versions

Internal Tracking #:

Resolution: None

Resolved in Build: : None

Duplicate of: None

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Description

An assignment of a TStringlist to itself clears its contents. Same behavior with a TList.

[System.Classes.pas]
------------
...
procedure TStrings.Assign(Source: TPersistent);
begin
  if Source is TStrings then
  begin
    BeginUpdate;
    try
      Clear;
...
------------

Steps to Reproduce:

Execute the following code and see that after the "SL.Assign(SL2)" the stringlist(s) are empty.

------------
var
  SL: TStringList;
  SL2: TStringList;
begin
  SL := TStringList.Create;
  try
    SL2 := SL;
    SL2.Add('Foo');
    ShowMessage(Format('SL.Count: %d;  SL2.Count: %d', [SL.Count, SL2.Count]));
    SL.Assign(SL2);          // Clears the stringlist.   "SL.Text := SL2.Text;" would work
    ShowMessage(Format('SL.Count: %d;  SL2.Count: %d', [SL.Count, SL2.Count]));
  finally
    SL.Free;
  end;
------------

Workarounds

Assign to a copy of the stringlist.

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