[fpc-pascal] TFPGMap retrieving values

Ryan Joseph genericptr at gmail.com
Fri May 1 16:12:59 CEST 2020

I've been starting to use the RTL so I'm not very familiar with it but I thought TFPGMap was supposed to be a hash table for fast lookup, so why does TFPSMap.Find using a binary search instead of computing a hash key and indexing into the array like that? Is this not the type I should be using in the RTL for a generic hash table? What even is TFPGMap supposed to be if it isn't a hash table?

function TFPSMap.Find(AKey: Pointer; out Index: Integer): Boolean;
{ Searches for the first item <= Key, returns True if exact match,
  sets index to the index of the found string. }
  I,L,R,Dir: Integer;
  Result := false;
  Index := -1;
  if not Sorted then
    raise EListError.Create(SErrFindNeedsSortedList);
  // Use binary search.
  L := 0;
  R := FCount-1;
  while L<=R do
    I := L + (R - L) div 2;
    Dir := FOnKeyPtrCompare(Items[I], AKey);
    if Dir < 0 then
      L := I+1
    else begin
      R := I-1;
      if Dir = 0 then
        Result := true;
        if Duplicates <> dupAccept then
          L := I;
  Index := L;

	Ryan Joseph

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