TDictionary weird behavior in delphi

Question

I have the following problem:

I fill in the dictionary with some values ​​and would like to return them in the exact exact order in which I filled them.

Somehow this does not work when I repeat the elements, they are sorted in an illogical order (IMDO).

After starting the following program:

program Project1; {$APPTYPE CONSOLE} {$R *.res} uses System.SysUtils, System.Generics.Collections; var Dictionary: TDictionary<LongWord, string>; aPair: TPair<LongWord, string>; begin Dictionary := TDictionary<LongWord, string>.Create; Dictionary.add(1, 'First Item'); Dictionary.add(2, 'Second Item'); Dictionary.add(3, 'Third Item'); Dictionary.add(4, 'Forth Item'); Dictionary.add(5, 'Fifth Item'); Dictionary.add($FFFFFFFF, 'Longword Item'); for aPair in Dictionary do writeln(aPair.Value); readln; end. 

I got the following results:

 Forth Item Longword Item First Item Third Item Second Item Fifth Item 

Am I doing something wrong?

Tested on XE5 and Rad Studio Berlin, same results.

Thanks for the help.

Answer 1

The Delphi dictionary class is unordered. It behaves as designed. If you want to keep an order, you need to use an ordered data structure. For example, an array or a list.

If you want to have ordered access as well as O (1) search, you will need to support two collections in tandem. One array or list for ordered access and in the tandem dictionary for O (1) search. Or, alternatively, find a library that offers an ordered implementation of a dictionary.