Difference between revisions of "Set"
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Revision as of 21:26, 27 April 2013
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;
simple data types |
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complex data types |