openvrml-develop

[openvrml-develop] Considering renaming node_class

[Braden M. <br...@en...>]

I've been reminded recently that the distinction between "node_class" 
and "node_type" can be confusing; and I'm inclined to believe this is 
mostly because of how they're named. OOP tends to treat the terms 
"class" and "type" as synonyms. But in OpenVRML, a node_class is very 
different from a node_type.

I believe node_type is pretty accurately named. It corresponds to what 
the VRML97 spec calls a "node type". node_class, on the other hand, 
doesn't exactly correspond to anything in the spec. A concrete 
node_class provides a sort of foundation for the implementation of a 
suite of node_types that share that implementation. As such, it is 
closest to the VRML spec's concept of a PROTO. However, while a PROTO 
could be considered a "kind of" node_class (and in fact OpenVRML 
implements PROTOs that way), not all node_classes are PROTOs.

So I am considering renaming "node_class". The frontrunner in my mind at 
the moment is "node_metatype". This class is responsible for creating 
node_types; and it can create n! distinct node_types, where n is the 
number of node interfaces supported by the node implementation.

"node_type_factory" has also been suggested. It is accurate; this class 
is a factory for node_types. However, it strikes me as less expressive 
than "node_metatype".

Opinions? Other suggestions?

Braden

Re: [openvrml-develop] Considering renaming node_class

[Reed H. <re...@in...>]

I looked at node_class a bit but don't remember exactly how it works,
but "factory" does imply a specific way of operating.  Could a
node_metatype in fact be a kind of node_type? Then you could just have
"nothing but node_types all the way down" :)

Either way, but yes, I did find the whole idea of node_class a bit
mysterious at first, partly because I didn't know what _class meant.
Most of us openvrml users won't need to deal with node_class anyway if
we're not creating new types of nodes, right?  So the documentation
could just say so and we could skip over it.

Reed



Braden McDaniel wrote:
> I've been reminded recently that the distinction between "node_class"
> and "node_type" can be confusing; and I'm inclined to believe this is
> mostly because of how they're named. OOP tends to treat the terms
> "class" and "type" as synonyms. But in OpenVRML, a node_class is very
> different from a node_type.
> 
> I believe node_type is pretty accurately named. It corresponds to what
> the VRML97 spec calls a "node type". node_class, on the other hand,
> doesn't exactly correspond to anything in the spec. A concrete
> node_class provides a sort of foundation for the implementation of a
> suite of node_types that share that implementation. As such, it is
> closest to the VRML spec's concept of a PROTO. However, while a PROTO
> could be considered a "kind of" node_class (and in fact OpenVRML
> implements PROTOs that way), not all node_classes are PROTOs.
> 
> So I am considering renaming "node_class". The frontrunner in my mind at
> the moment is "node_metatype". This class is responsible for creating
> node_types; and it can create n! distinct node_types, where n is the
> number of node interfaces supported by the node implementation.
> 
> "node_type_factory" has also been suggested. It is accurate; this class
> is a factory for node_types. However, it strikes me as less expressive
> than "node_metatype".
> 
> Opinions? Other suggestions?
> 
> Braden
> 
> 
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Re: [openvrml-develop] Considering renaming node_class

[Braden M. <br...@en...>]

On Sat, 2005-11-19 at 16:25 -0500, Reed Hedges wrote:
> I looked at node_class a bit but don't remember exactly how it works,
> but "factory" does imply a specific way of operating.  Could a
> node_metatype in fact be a kind of node_type? Then you could just have
> "nothing but node_types all the way down" :)

A node_class is a factory for node_types. node_class and node_type have
distinct roles. A node_type identifies a subset of the interfaces that
can be supported by a node implementation and is a factory for nodes
that have those interfaces. The node_class gives the node implementation
identity and provides a way of creating node_types.

Different node types can share implementation logic--that's not unique
to OpenVRML; that's just the way VRML97 works. node_class is a place to
hang that shared implementation logic.

> Either way, but yes, I did find the whole idea of node_class a bit
> mysterious at first, partly because I didn't know what _class meant.

I agree it's vague. So is _metatype better? If not, then what?

> Most of us openvrml users won't need to deal with node_class anyway if
> we're not creating new types of nodes, right?  So the documentation
> could just say so and we could skip over it.

That's true to an extent; though API changes that will be going in soon
will raise its visibility a bit: I'll be making it possible to add and
retrieve node_classes to/from a browser instance. Most casual users
probably won't be interested in this functionality; but it does expose a
rather important dimension of flexibility to those who need it.

-- 
Braden McDaniel                           e-mail: <br...@en...>
<http://endoframe.com>                    Jabber: <br...@ja...>