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

Report #: 75851

Status: Closed

TObjectDictionary.Remove frees wrong values

Project: Delphi

Build #: 12.0.3420.21218

Version: 12.1

Submitted By: David Muller

Report Type: Basic functionality failure

Date Reported: 7/16/2009 8:14:18 AM

Severity: Serious / Highly visible problem

Last Updated: 3/20/2012 2:24:39 AM

Platform: All platforms

Internal Tracking #: 269410

Resolution: Fixed (Resolution Comments)

Resolved in Build: : Delphi 2010

Duplicate of: None

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Total Votes: 6

Description

Calling TObjectDictionary.Remove when the dictionary owns values may result in the wrong value being freed.

Steps to Reproduce:

ype
  TObj = Class
  Private
    fName: String;
  Public
    Constructor Create(const aName: String);
    Destructor Destroy; override;
  End;

{ TObj }

constructor TObj.Create(const aName: String);
begin
  fName := aName;
end;

destructor TObj.Destroy;
begin
  Form1.Memo1.Lines.Add(fName + ' being destroyed');
  inherited;
end;

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
Var
  Dict: TObjectDictionary<String, TObj>;
begin
  Dict := TObjectDictionary<String, TObj>.Create([doOwnsValues]);
  Dict.Add('Part1', TObj.Create('Part1'));
  Dict.Add('Part2', TObj.Create('Part2'));
  Dict.Add('Part3', TObj.Create('Part3'));
  Dict.Add('Part4', TObj.Create('Part4'));
  Dict.Remove('Part1');
  Memo1.Lines.Add('----');
  Dict.Free;
end;

Expected Output:
Part1 being destroyed
----
.
.
.

Actual Output:
Part3 being destroyed
-----
.
.
.

+ Exception thrown when the dictionary tries to double free Part3.

Workarounds

Use a StringList instead - but no automatic lifetime management & lots of casting required.

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