Correct way to dispose of TDictionary after sorting it into an array

Question

I have a TDictionary like

target_results : TDictionary<longint,double>;

After populating it I need to sort the results. I'm doing it like this

type
  TSearchResult = TPair<longint,double>;

var
 target_results_array : TArray<TSearchResult>;

target_results_array:= target_results.ToArray;
TArray.Sort<TSearchResult>(best_knowledge_search_results,
                    TComparer<TSearchResult>.Construct(
                              function(const L, R: TSearchResult): Integer
                              begin
                                if L.Value < R.Value then Result := 1 else if L.Value > R.Value then Result := -1 else Result := 0;
                              end
                    ));

It's all working as expected. My question is how do I dispose of the TDictionary and the TArray without any leaks? Currently I'm just doing

target_results.Free;

I don't understand why you use a dictionary. This looks like it should be TList. — David Heffernan, Aug 04 '13 at 12:19
@DavidHeffernan I'm performing a bunch of queries to determine a final score. Each query brings a set of sub-total scores. I use TDictionary.AddOrSetValue to add a new entry or add the sub-total to the existing key. Would you say this is the most efficient structure to fit this? Thanks! — Miguel E, Aug 04 '13 at 12:25
If you are performing key lookup then a dictionary is good. Of course, that aspect is not in the Q, hence my query. But it seems you've got the right data structure. — David Heffernan, Aug 04 '13 at 12:32
Just to make clear: AddOrSetValue doesn't add the sub-total to the existing value, it will simply overwrite any existing value with the new sub-total. — Uwe Raabe, Aug 04 '13 at 16:09
@UweRaabe Thanks. I'm using TryGetValue to retrieve a possible already existing value, before adding the sub-total. — Miguel E, Aug 04 '13 at 19:53
This just reminds me how poor our Collections unit is. :-( This problem cries out for a default dictionary implementation. Even without one if we had a function that returned a specified value if a key wasn't found you could just do your totals as: target_results.Items(index) := target_results.get(index, 0) + subtotal. Actually since items has an exception we'd target_results.AddOrSetValue(index, target_results.get(index, 0) + 1). Yuck.. TDictionary needs a lot of work. We also need a sort function that takes a key value rather than a custom comparison function so you could sort in just 1 line — alcalde, Aug 05 '13 at 06:04

score 6 · Accepted Answer · answered Aug 04 '13 at 12:16

Since your data is longints and doubles, which are both value types, freeing the dictionary will work fine. Your array will contain a copy of the original values, and you don't need to worry about losing or corrupting anything.

If you had object types instead, and you had a TObjectDictionary that owned the objects, then you'd have to worry about this sort of thing, but for purely numeric data, you're fine.

Correct way to dispose of TDictionary after sorting it into an array

1 Answers1