I went and looked at the assembly code for this - you are right - this will not cause an exception (I even tried it).
The main reason it works is that Delphi does not need a valid object pointer to call .Free - it is not a virtual method. If Free were a virtual method, then a valid object pointer would be required to call free. Doug Totoliciu Denis Dan wrote: > When I have posted that the following lines: > > Obj := Nil; > Obj.Free(); > > do not raise an exception, I didn't have Delphi at > hand; but I knew that inside TObject.Free() it is > written something like this: > > procedure TObject.Free(); > begin > if Self <> Nil then > Self.Destroy; > end; > > The call to Free() through Obj (that is Nil) goes OK > because: > 1. Free() is not a virtual method; and as we all know, > the binding is done at compile time. That means there > is no need to access a VMT. > 2. Every method of a class has a hidden parameter; and > that parameter is Self. When calling Free, there is > no need that Obj is different then Nil as Obj (named > Self inside the method Free()) is passed as parameter. > > Obj.Free() would raise an error when Obj points to a > zone of memory that is not allowed to be accessed. >
