[fpc-pascal] TList: newbie question

[Paul Nicholls]

----- Original Message ----- 
From: "Bart" <bartjunk64 at gmail.com>
To: "FPC-Pascal users discussions" <fpc-pascal at lists.freepascal.org>
Sent: Wednesday, April 01, 2009 10:12 PM
Subject: [fpc-pascal] TList: newbie question


> Hi,
> 
> I never used TList before, so I'm not sure if this is correct.
> 
> I constructed a TlcTextCache class that basically stores objects of
> type TLcText in a TList.
> A TlcText object is create with TLcText.Create(FileName).
> 
> My questions:
> - I add my TlcText objects to the list by TList.Add(SomeTlcTextObject)
> - I read from the list by SomeTlcTextObjetc :=
> TlcText(TList.Items[Index]) (casting it at compiletime)
> Is this the way I am supposed to do that and is it safe explicitly
> casting the TList.Item[Index] to the TlcText type (I know I only add
> this type of objects to the list).
> 
> Here's the relevant part of the code:
> 
>  TLcText = class
>  [snip]
> 
>  TLcTextCache = class
>  private
>    FCacheList: TList;
>  protected
>    function IsCached(const FileName: String): Boolean;
>    function CacheIndex(const FileName: String): Integer;
>    function AddFile(const FileName: String): Boolean;
>    function GetCacheCount: Integer;
>    function GetLcText(const FileName: String): TLcText;
>  public
>    constructor Create; virtual;
>    destructor Destroy; override;
>    property Count: Integer read GetCacheCount;
>  end;
> 
> { TLcTextCache }
> 
> function TLcTextCache.IsCached(const FileName: String): Boolean;
> begin
>  Result := CacheIndex(FileName) >= 0;
> end;
> 
> function TLcTextCache.CacheIndex(const FileName: String): Integer;
> var
>  i: Integer;
>  LcText: TLcText;
> begin
>  Result := -1;
>  for i := 0 to FCacheList.Count - 1 do
>  begin
>    LcText := TLcText(FCacheList.Items[i]);
>    if LcText.FileName = FileName then
>    begin
>      Result := i;
>      Break;
>    end;
>  end;
> end;
> 
> function TLcTextCache.AddFile(const FileName: String): Boolean;
> begin
>  Result := FCacheList.Add(TLcText.Create(FileName)) >= 0;
> end;
> 
> function TLcTextCache.GetCacheCount: Integer;
> begin
>  Result := FCacheList.Count;
> end;
> 
> function TLcTextCache.GetLcText(const FileName: String): TLcText;
> var Index: Integer;
> begin
> Index := CacheIndex(FileName);
> if (Index >= 0) then
>   Result := TlcText(FCacheList.Items[Index])
> else
>   Result := nil;
> end;
> 
> constructor TLcTextCache.Create;
> begin
>  inherited Create;
>  FCacheList := TList.Create;
> end;
> 
> destructor TLcTextCache.Destroy;
> var
>  i: Integer;
>  LcText: TLcText;
> begin
>  for i := FCacheList.Count - 1 downto 0 do
>  begin
>    LcText := TLcText(FCacheList.Items[i]);
>    LcText.Free;
>    LcText := nil;
>  end;
>  FCacheList.Free;
>  inherited Destroy;
> end;
> 
> 
> So far testing this construction gave no obvious errors (but as we all
> know that is no garantee that the code is not flawed at some point)
> and no memory leaks (using heaptrc).
> 
> Bart

As far as I can see it all looks A-OK :)
cheers,
Paul