On Thu, 08 May 2014, Stephen wrote: > Looking at the thread "New syntax for using variables arguments in a > function call" I realized that I needed to really brush up on my > somewhat marginal understanding of the evolving (a good thing) GAMBAS > and OOP. Not fully understanding "SUPER" (I've never used it but can see > a use for it) I trotted off to Google and the GAMBAS documentation, > where much reading was done, and (as usual) more questions raised.
If you write a class and inherit from another class, you can override methods and properties in your inheriting class. However, sometimes the inherited class does a pretty good job already and you don't want to reinvent the wheel for doing something. That's when Super comes into play because Super knows where the method and property implementations of the inherited class (the super class) are. So you can still call methods of the super class in your subclass that you have actually just overridden. In the example below, you want to skim data in ListBox' Add() method but you don't want to implement the actual addition of a new element so you resort to the original ListBox' Add() implementation - which is available as Super.Add() and knows how to do the thing. > Studying the "SUPER" example at http://gambasdoc.org/hemp/lang/super, > I wondered at the purpose of a collection that seems not to be used but > once and some syntax in it's use in the example, which didn't make any > sense to my old brain. Below is a snippet from the example (where $cPos > is a collection, $aKey an Array of String Objects (I think) and Key a > string object; > > $cPos.Clear > $cPos[Key] = $aKey.Count > $aKey.Add(Key) > > OK, the first line clears the collection, got it, and the last line > adds the contents of "String" to $aKey, got that.... but what does the > second line do? It looks like it is adding the count of elements in > $aKey to the collection $cPos... but in OOP I would use a method call > i.e. $cPos.Add(Key,Key). Oh, and in trying to implement the example > GAMBAS (3.5.3) complained that "ListBox.Add is incorrectly overridden". > $cPos[Key] = $aKey.Count followed by $aKey.Add(Key) will store the *index* of Key in the $aKey array in the $cPos collection, indexed by the *value* of the key. (Think about it.) That means if the user gives you a Key, you can look up the index of that key in the $aKey array using $cPos[Key], i.e. the statement $aKey[$cPos[Key]] will always return Key (or raise an error, but see below for that). This also explains why the Collection is named $cPos. Not sure what that implies or what we can do with it and how $cPos.Clear() fits into the picture because it already deletes that additional information we collected... Either I don't get it or the example is just broken (I'd prefer the second option, of course :-)). Regards, Tobi -- "There's an old saying: Don't change anything... ever!" -- Mr. Monk ------------------------------------------------------------------------------ Is your legacy SCM system holding you back? Join Perforce May 7 to find out: • 3 signs your SCM is hindering your productivity • Requirements for releasing software faster • Expert tips and advice for migrating your SCM now http://p.sf.net/sfu/perforce _______________________________________________ Gambas-user mailing list Gambas-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/gambas-user
