Associative arrays with a class type as key

[simone]

Sometimes I need to implement associative arrays. For this purpose, as far as I know, I should use TFPGMap available in FGL unit or TDictionary present in rtl-generics unit. However I noticed that TFPGMap does not allow TKey to be a class in the pair <TKey,TValue>. Did I understand correctly? Thanks in advance for responses.

[LemonParty]

You can use this construction if the type of values is the same:

Code: Pascal  [Select][+][-]

1. type
2.  TKeys = (apple,orange,banana);
3.  TAsArray = array[TKeys]of String;
4. var A: TAsArray;
5. begin
6.  A[apple]:= '1';
7.  A[banana]:= 'monkey';
8.  Writeln(A[apple],A[banana]);
9.  readln;
10. end.
11.  

[Thaddy]

You mean:

Code: Pascal  [Select][+][-]

1. {$ifdef fpc}{$mode delphi}{$H+}{$endif}
2. uses generics.collections;
3. type TMyClassMap = TObjectDictionary<Tobject, string>; // a map is a dictionary!
4. var
5.   map:TMyClassmap;
6. begin
7.   map := TMyClassmap.Create([doOwnsKeys, doOwnsValues]);    
8.   try
9.     //
10.   finally
11.     map.free;
12.   end;    
13. end.

That would be possible in  fgl too, but there you need to overload some operators, so it is more work.

[simone]

Thanks Thaddy. In the past I used rtl-generics as in your example, for associative arrays/maps/dictionaries. Although rtl-generics is better than FGL, I generally tend to use the latter as it is part of the standard distribution of Lazarus. I hope in the future also rtl-generics will be included.

[Thaddy]

rtl-generics is already in trunk. for 3.0.4. the OPM has a version.

[simone]

This is good news. Thanks for the update.