Delphi:Bitfield Booleans

type TExplainThat =class(TObject)
private
   FFlags:Cardinal;
   function GetFlags(Index:Integer):Integer;
  procedure SetFlags(Index:Integer;Value:Boolean);
public
    property Flags[Index:Integer]:Boolean read GetFlags writeSetFlags;
end;

function TExplainThat.GetFlags(Index:Integer):Integer;
begin
Result:=(FFlags and (1 shl Index) > 0);
end;

procedure TExplainThat.SetFlags(Index:Integer;Value:Boolean);
begin
    FFlags:=(FFlags xor ($7FFFFFFF and (1 shl Index))) or (ord(Value) shl Index);
end;

• The GetFlags method is easy to understand. We simply check to see if the bit at position Index is turned on.
• SetFlags is rather more complicated. In the first part - before the or - we turn off the bit at position Index. With this done we then turn it on again if Value is true. Doing some math on ord(Value) is more efficient than testing Value in an if..then..else block.

This technique enables up to 31 booleans to be stored in a 4 byte integer - a saving of 27 bytes! The performance hit incurred by doing some additional math is never noticeable - not even in the most complex of applications.