Ryan Joseph <generic...@gmail.com> schrieb am Fr., 7. Juni 2019, 14:00:
> > > > On Jun 7, 2019, at 2:51 AM, Michael Van Canneyt <mich...@freepascal.org> > wrote: > > > > What kind of behaviour are you referring to. > > Something wrong with my mail server causing your server to block me (Jonas > said my server didn’t handle greylisting correctly). Easier to just re-sub > using gmail for now. > Michael meant this: > But my point is Pascal allows this kind of behavior so why are properties > different? > > > >> Who cares if there is an additional level of indirection? > > > > Because the indirection may not be there. The compiler cannot guarantee > that, thus leading to access violations. > > > > You can use a getter function to get the desired property. In the getter > you > > can decide what to do: create the b instance (sometimes a valid choice) > or raise an error. > > > > But the compiler cannot take this decision for you, so b.x is not > allowed. > > I really have to question the wisdom of this. The code below works in > 3.0.4 and is completely safe. I understand there was delphi compatibility > and problems with published properties however but that could have been > worked around easily. Maybe it’s a not big deal in the grand scheme of > things but writing boiler plate like getters/setters is not fun. > > type > TB = class > x: integer; > end; > > type > TA = class > private > b: TB; > public > property x: integer read b.x write b.x; > procedure AfterConstruction; override; > end; > > > procedure TA.AfterConstruction; > begin > b := TB.Create; > end; > > var > a: TA; > begin > a := TA.Create; > a.x := 100; > writeln(a.x); > end. > Only because this example appears safe does not mean that the whole concept is safe. A class might initialize b only later on and with a direct property you'll only get an access violation. So you'll need a getter anyway to provide a better exception type. Or to dynamically create the object instance. I see no reason to revert this change. Regards, Sven >
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