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implicit typecasting

Posted on 2001-06-22
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Last Modified: 2010-04-06
Hi

I have created a new type TMyType. Now I want to have a random number of this type in a list, array, etc.

I first used a TObjectList, which worked fine, but I got some ugly code, because I had to typecast to my type the whole time.
Like this (ObjectList[i] as TMyType).SomeProperty

I could use an array to make the code a bit nicer, but as I add and remove objects an array won't do.

Is it possible to create an ObjectList that works with TMyType.
It would be perfect if something like templates from C++ were around.
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Question by:bnz
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4 Comments
 
LVL 8

Expert Comment

by:TOndrej
ID: 6217458
You can derive your own TMyTypeList from TList to hold TMyType type elements just as TObjectList does for TObject type elements...
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LVL 9

Accepted Solution

by:
ITugay earned 300 total points
ID: 6217872
Hi bnz,

here is a short sample how to create list to keep your objects

  // your object
   TMyType = class(TObject)
     Name: String;
   ...
   end;

  // list that keeps your objects
  TMyTypes = class(TObjectList)
  private
      function GetItem(Index: Integer): TMyType;
  public
     property Items[Index: Integer] read GetItem; defsult;
  end;

implementation

function TMyTypes.GetItem(Index: Integer): TMyType;
begin
  Result := TMyType(Inherited Items[Index]);
end;

......
var
  MList: TMyTypes;
......
  MList[10].Name := 'Some name';
 
-------
Igor.  
0
 
LVL 14

Expert Comment

by:AvonWyss
ID: 6220383
Another way to do implicit typecasts instead of explicit ones it to use a normal TList and to have a temporary variable of TMyType. Since TList deals with generic pointers, you can assign them to and from a TMyType variable without typecast, thus making Delphi do an invisible typecast.
0
 
LVL 4

Expert Comment

by:DMN
ID: 6220463
Also it's possible to use TCollection and TCollectionItem
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