Re^3: Object Method Call

But there is a slightly difference between display($self) and $self->display(), when a class XY inherits from MyTest and implements it's own display() method. display($self) calls MyTest::display() even when invoked on an instance of XY, whereas $self->display() calls XY::display() when invoked on an instance of XY. So, one could say that display($self) breaks inheritance. This is often bad, but sometimes, it can be a useful trick.

Alexander

--
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)

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Re^4: Object Method Call by ikegami (Patriarch) on Jul 27, 2009 at 19:40 UTC
That usually occurs when you're overriding a method, in which case `$self->SUPER::display();` will do the trick.	[reply] [d/l]
Re^5: Object Method Call by afoken (Chancellor) on Jul 27, 2009 at 19:54 UTC
Yes, SUPER:: is the usual way to access the super method. But the evil trick of invoking a method as a function with the object as first argument is different. It completely prevents overriding that method, no matter how deep the inheritance tree is. I know it is evil, confuses everyone, and is a sure sign of a broken design. But in very rare cases, it can be useful, even if it breaks the design even more. See Re^5: Object Method Call. Alexander -- Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)	[reply]
Re^4: Object Method Call by AnomalousMonk (Archbishop) on Jul 27, 2009 at 14:56 UTC
So, one could say that `display($self)` breaks inheritance. It certainly does that if `display` is a method. This is often bad, but sometimes, it can be a useful trick. Hm. Well, I would agree with the word bad, but I think I would delete often unless the goal of the trick is to confuse the heck out of yourself and everyone else. For me, it's hard enough to keep everything in OO programming straight without deliberately trying to trick myself. I'm curious: Can you give an example of how this trick might be productively used?	[reply] [d/l] [select]
Re^5: Object Method Call by afoken (Chancellor) on Jul 27, 2009 at 19:33 UTC
Hmmm, I remember having used that trick only once in my life, but the project has been administrated to dead (long story about clueless interns working as admins, dieing harddisks, missing monitoring systems, and insufficient backups). It was a crude class hierarchie that should have been refactored. At one point, the usual inheritance would have broken things if a certain method was overwritten. I don't remember the details and the sources are lost, but it was nasty and had a comment marking that trick as "evil but required". Alexander -- Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)	[reply]
Re^6: Object Method Call by AnomalousMonk (Archbishop) on Jul 28, 2009 at 06:55 UTC
evil but required Ah, yes. Now I know just the code you are talking about.	[reply]