Set

Introduction

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.

Manipulating sets

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(TSpeed)..High(TSpeed)];
  begin
    CanBeSlow := (spVerySlow in SomeSpeeds) or (spSlow in SomeSpeeds);
  end;