G'day tusker,

Welcome to the Monastery.

Using class names like A, B, C and D, doesn't make it easy to visualise your overall class structure.

In general terms, A::B::C doesn't imply that B inherits from A nor that C inherits from A::B; it does, however, imply that B is somehow related to A and C is somehow related to A::B.

Having said that, it often makes sense to use naming to logically separate concerns. For instance, A might compose B::C or B::D while both B::C and B::D inherit from B.

Consider these contrived classes: 

Building
Building::House
Building::Shed
Building::Garage
Vehicle
Vehicle::Car
Vehicle::Train
Vehicle::Motorcycle
Door
Door::Hinged
Door::Sliding
Door::Roller

[download]

The various Building::* and Vehicle::* classes could compose zero, one or more Door::* classes.

By sticking with your current class structure, you could end up with a huge number of classes such as this: 

Building
Building::House
Building::House::Door
Building::House::Door::Hinged
Building::House::Door::Sliding
Building::Shed
Building::Shed::Door
Building::Shed::Door::Hinged
...
Vehicle
Vehicle::Train
Vehicle::Train::Door
Vehicle::Train::Door::Hinged
Vehicle::Train::Door::Sliding
...

[download]

This quickly starts to become unmanageable. Building::House::Door, Building::Shed::Door and Vehicle::Train::Door will probably have duplicated code; as will Building::House::Door::Hinged, Building::Shed::Door::Hinged, Vehicle::Train::Door::Hinged, and so on. Throw in a variety of Lock, Handle, etc. subclasses and you're facing a maintenance nightmare.

I'd recommend spending a bit more time on your class design before writing any code. Class names with duplicated portions will probably equate to duplicated code which you should endeavour to avoid.

[A note on nomenclature. You used the term "composition" in your question and I continued its use; however, in the strictest sense, that may be inappropriate in some cases. There are other types of relationships (e.g. "aggregation", "association", "delegation"): at times, it's important to be specific about which you're referring to. You may already know about these; if not, most introductory OO texts will describe them.]

— Ken

In reply to Re: Perl modules hierarchy and composition by kcott
in thread Perl modules hierarchy and composition by tusker

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