Class hierarchy problem

[BrJohan]

On 06/08/2013 16:02, Chris Angelico wrote:

>> My classhierarchy is like a multilevel tree where each non-leaf node (class)
>> is given knowledge about its nearest subclasses and their 'capacities'.
>>
>> So, my idea is to let the 'upper' class recursively choose which of its
>> nearest subclasses is the 'correct' one, until approaching a 'leaf' class
>> from which the instance should be created. And, given my knowledge that a
>> solution along the lines of this idea has been designed and was working, I'm
>> still hopeful ... (or I'll have to investigate all those old backup-DVDs)
>
> [ responding on-list - I hope it was mere oversight that had this come
> privately to me alone ]
>
> This is code smell; this recursive search for the "right" class seems
> likely to be wrong. Can you have the classes perhaps register
> themselves in some way? On what basis is a superclass to determine
> that one of its subclasses should handle this request?
>
> ChrisA
>


Consider a botanical classification system (somewhat analogous to my 
'problem' as it effectively is related to classification of entities):

A Domain should know about its Kingdoms,
a Kingdom should know about its Phylums,
...
a Genus should know about its Species.

Of course it is possible to implement such a decision tree as a 
'factory'. However, I would rather prefer to encapsulate those decisions 
at the class level where they 'belong'.

BrJohan