“Documented” in Delphi 2010, [Archive.is] Generics.Collections.TDictionary.ExtractPair – RAD Studio VCL Reference, and functioning bug-free since Delphi XE2, but still hardly documented, [Archive.is] System.Generics.Collections.TDictionary.ExtractPair – XE2 API Documentation is the easiest way to get a value out of a dictionary and updating it, even if it does not exist.
ExtractPair extracts the TPair<TKey, TValue> if it exists (and removes it from the dictionary) or returns a Default initialised one if not. Though Default is still not documented, you can find an example at [WayBack] How to properly free records that contain various types in Delphi at once? – Stack Overflow.
Example code for ExtractPair:
FEceptionDictionary := TDictionary<TExceptionKey, Integer>.Create();
...
var
ExceptionCountPair: TPair<TExceptionKey,Integer>;
begin
TMonitor.Enter(FEceptionDictionary);
try
ExceptionCountPair := FEceptionDictionary.ExtractPair(ExceptObj.ClassType); // extracts and removed from dictionary!
FEceptionDictionary.Add(ExceptionCountPair.Key, ExceptionCountPair.Value + 1); // use Value as count
finally
TMonitor.Exit(FEceptionDictionary);
end;
end;
In Delphi 2010 and XE it was buggy (see [WayBack] QualityCentral 80947: TDictionary.ExtractPair Fails and creates memory leak via [WayBack] generics – Delphi TPair Exception – Stack Overflow), but since then it works fine, and now is properly documented:
[WayBack] System.Generics.Collections.TDictionary.ExtractPair – RAD Studio API Documentation
Returns the
TPair<TKey,TValue>pair with the specifiedKeyand [WayBack] removes the returned pair from a dictionary.If the dictionary does not contain the specified
Key, the returned pair contains a defaultTValue.
–jeroen
The Wiert Corner - irregular stream of stuff 