CODEWITHSUNDEEP
delphi
zeus
zeus

Reputation: 13367

What exactly is Tclass?

In my program I do:

var aObj: Tobject;
var aObjClassType: Tclass;
....
aObjClassType := aObj.ClassType;
....
aObj.free;
aObj := nil;
....
showmessage(aObjClassType.Classname);

this work but I m not quite sure If this is correct, especially when i read the function TObject.ClassType

function TObject.ClassType: TClass;
begin
  Pointer(Result) := PPointer(Self)^;
end;

So does freeing aObj will not also free the aObjClassType ?

Upvotes: 1

Views: 985

Answers (1)

David Heffernan
David Heffernan

Reputation: 612993

A TClass is a class. A TObject is an instance. So obj.ClassType returns the class, that is the type, of the instance obj.

Note that this is the runtime type of the instance rather than the type of the obj reference variable. This is relevant when using polymorphism. So if you write 

var
  shape: TShape;
.... 
shape := TSquare.Create;

Then shape.ClassType returns TSquare even though the shape variable is TShape.

So does freeing aObj will not also free the aObjClassType?

No. Classes are static and created when the module loads and destroyed when the module unloads.

For more detail read the documentation: http://docwiki.embarcadero.com/RADStudio/en/Classes_and_Objects_(Delphi)#TObject_and_TClass

Upvotes: 6

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