So when you say, "there's not meaningful way to generically clone an object in meaningful way", the emphasis is on "generically". That is, the semantics of cloning an object are specific to the object, not generic. If that's what you mean, then I'd agree.
Vince > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Sean Corfield > Sent: Friday, May 13, 2005 6:11 PM > To: [email protected] > Subject: Re: [CFCDev] Confusion about persistent CFCs > > On 5/13/05, Vince Bonfanti <[EMAIL PROTECTED]> wrote: > > I'm not sure I understand what you mean by this. By "state" > you mean > > the object attributes (instance variables). Wouldn't > cloning an object > > merely copy the current state? Isn't this how > Object.clone() works in > > Java--thus inherently supporting a way to "generically 'clone' an > > object in (a) meaningful way"? > > But that's a default behavior that any vaguely complex class > needs to override. Most objects of any complexity have two > types of state - one you can (and should) clone and one that > needs to be reset or recalculated as part of a cloning > operation. I know there's a few whitepapers out there that > cover this issue but I'm coming up blank right now. > > Consider composition. A car has-a engine. So you create an > engine object and you create a car object and store a > reference to the engine inside the car. Now you clone the > car. The clone has to copy all of the car's state and *clone* > the engine - otherwise two cars will share the same physical > engine object! Now consider that your car has a reference to > a manufacturer object. You don't want to clone that when you > copy the car, you just want to copy the reference - the > manufacturer is a singleton and all Mercedes should refer to > the same Mercedes manufacturer object. Even if you just say > that clone() should copy simple data and call clone() on > complex data, you then have > engine.clone() that returns a copy of itself but > manufacturer.clone() returns itself, not a copy. > > Does that example help? > -- > Sean A Corfield -- http://corfield.org/ > Team Fusebox -- http://fusebox.org/ > Got Gmail? -- I have 50, yes 50, invites to give away! > > "If you're not annoying somebody, you're not really alive." > -- Margaret Atwood > ---------------------------------------------------------- You are subscribed to cfcdev. To unsubscribe, send an email to [email protected] with the words 'unsubscribe cfcdev' as the subject of the email. CFCDev is run by CFCZone (www.cfczone.org) and supported by CFXHosting (www.cfxhosting.com). CFCDev is supported by New Atlanta, makers of BlueDragon http://www.newatlanta.com/products/bluedragon/index.cfm An archive of the CFCDev list is available at www.mail-archive.com/[email protected]
