If I have read you right then your base class has foreknowledge of your subclasses. The reason being you can either instantiate the sub class or pass a parameter to the base class and it decides what class to give you.

Assuming this is correct:

This would be my reason why you should avoid putting your base class and your factory in the same class. The purpose of a class hierarchy, in my opinion, is that if you were to line them up (single level for simplicity): 
A     (base)
|
B      inherits
|
C      inherits

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Then as you go down the chain, you should be adding functionality and your classes become more *specific*.

Each class should have knowledge of its parent(s) but surely have none of its children? Your structure requires that the base class has knowledge of all classes that inherit from it (and possibly, its deepest descendants <-- though I doubt it).

I would argue that you need to think deeper regarding why you would want to merge a factory and your base class together. IMHO its better to have a separate factory that has 'knowledge' of the chain in question and can 'do the right thing'.

Of course, YMMV as it depends on your class hierarchy. I've only done horizontal class factories: 
         A
         |
  +---+--+---+---+
  B   C      D   E     <---------- Factory picks b,c,d or e

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Whereas yours looks like: 
A     (base)
|
B     -+
|      |
C      |-- Factory can handle the chain (only B and C shown)
      -+

[download]
But thats another story ;).

In reply to Re: Constructor/Factory Orthodoxy by simon.proctor
in thread Constructor/Factory Orthodoxy by mojotoad

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