A Set encodes many values from an enumeration into an Ordinal type.
For example let's consider this enumaration:
TSpeed = (spVerySlow,spSlow,spAVerage,spFast,spVeryFast);
And this set:
TPossibleSpeeds = set of TSpeed
The TPossibleSpeeds can be defined as constant in right brackets:
const RatherSlow = [spVerySlow,spSlow]; RatherFast = [spFast,spVeryFast];
RatherSlow and RatherFast are some Set of TSpeed.
Usually two compiler functions are used to manipulate a set: Include(ASet,AValue) and Exclude(ASet,AValue).
var SomeSpeeds = TPossibleSpeeds; begin SomeSpeeds := ; Include(SomeSpeeds,spVerySlow); Include(SomeSpeeds,spVeryFast); end;
Sets cannot be directly manipulated if they are published. You usually have to make a local copy, change the local copy and then to call the setter.
procedure TSomething.DoSomething(Sender: TFarObject); var LocalCopy = TPossibleSpeeds; begin LocalCopy := Sender.PossibleSpeeds; // getter to local Include(LocalCopy,spVerySlow); Sender.PossibleSpeeds := LocalCopy; // local to setter. end;
The Keyword in is also used to test if a value is in a set. It's usually used in this fashion:
var CanBeSlow: Boolean; const SomeSpeeds = [Low(TPossibleSpeeds)..High(TPossibleSpeeds)]; begin CanBeSlow := (spVerySlow in SomeSpeeds) or (spSlow in SomeSpeeds); end;