For your second feature request it just needs a method added to THashSet<T> that retrieves the stored item based on the passed key.
> On 27/03/2025 12:28 CET Martin Frb via fpc-devel > <fpc-devel@lists.freepascal.org> wrote: > > > There are 2 features, I am missing. > > And I can't see a way to add them via subclassing, as the internal > FItems array is private, and neither TItem, nor TPair can be gotten by > the integer index into that array. > > 1) AddOrGetPointerToEmpty > This would actually just be to try and see if it gives any benefit in > performance. > > There is TryAdd() > But, the caller must already have a new value, that it can pass for that > key. > > However, if the dictionary already has a value for that key, then the > existing value may be enough, > So the caller ends up > NewVal := CreaterNewValSpendingTime; > if not Dictionary.TryAdd(TheKey, NewVal) then > NewVal.Destroy; > > Alternatively the caller can do > If not Dictionary.ContainsKey(TheKey) then ... > > But the latter then means, that "TheKey" need to be hashed twice, if a > new value needs to be added (Even though the hash could already be known). > > If there was a function > GetItemPointer(AKey: TKey; out APtr: PValue): boolean; > > which returns True, if Akey was found and therefore APtr points to > existing Data, while otherwise APtr points to the empty slot, where the > data can be copied to. > > > > 2) Key and Data to be the same. > > Lets say I have lots of data, to which I have pointers (e.g. instances > of some object). > Now when I have such a pointer, I want to know if I had a previous > pointer to the same data. (even if the new pointer points to a copy of > the data at a new location). > > I could do TDictionary<TMyClass, TMClass> > I need to have my own IEqualityComparer, so I don't compare the > pointers, but the data in the object. (That I can do). > > But now I need to do > MyDict.Add(val, val); > Which means the same value is stored as pointer and data => doubling mem > requirements. > > What I would need is > - set TData to "record end" (zero size) > - be able to retrieve the existing key, for another key that returns > equal to the stored key > > So instead of > MyVal := Dict.Items[AKey]; > > I need > ExsitingKey := Dict.Keys[ANewKey]; > > Obviously since the key is the data, my IEqualityComparer can do proper > comparison, so even if the hash clashes, the pointed to data can be > compared. > _______________________________________________ > fpc-devel maillist - fpc-devel@lists.freepascal.org > https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel _______________________________________________ fpc-devel maillist - fpc-devel@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
