Simonson, Lucanus J wrote:
Joel wrote:
That's very good. I'm not quite sure about inheritance though.
You can override it with your own, of course, through the template inheritance generic interface.
P.S. my point2d data structure is a class encapsulated array of size
With the restriction that it has to be indexable by a runtime int? That is a severely limited concept of a point, I would say. And, again, I find the need for inheritance dubious. Inheritance gives you tight coupling. Something that you'd want to avoid when adopting a 3rd party type. It is possible to adopt a 2d-point from library A and library B without ever touching them. That's the very essence of generic programming.
I put a lot of thought into the implications of inheritance, believe me. There is no restrition that it has to be indexable by a runtime int.
Hmm. I was confused by your earlier post, it seems:
Moreover, the technique you are proposing works fine at compile time, but won't work if the axis of the coordinate you are accessing is a runtime parameter: int my_axis = 0; get<my_axis>(pt); will throw an error. We specify the axis we access at run time. If we specify a constant it should compile away and be light weight. gcc 4.2.1 still needs us to play with the compiler flags to get decent inlining. pt.get(orient.getPerpendicular()); //orientation determined at run time. My scanline algorithm actually parameterizes the orientation of the scanline at runtime, so you can sweep left to right or bottom to top.
[snip]
All this seems like overkill with simple point2d data types but when you have polygons that are sequences of vertices it becomes a Rosetta stone of type inter-compatibility and a mechanism for getting legacy data in and out of algorithms in a generic, zero cost of abstraction way that is minimal effort and very productive (not error prone.) When you realize that my Polygon concept class uses my Point concept class to interact with its vertices the whole picture suddenly becomes clear. Sometimes it is useful to have a polygon that is a linked list of points. Sometimes it is useful to have a vector, sometime it is useful to have a compressed storage for polygon data. The polygon concept class is the glue that can really tie everything together and make it all work together as smooth as butter.
By the way if you have a 3D point you can view it as a 2D point (because conceptually it is a 2D point with extra semantics.) I do that all the time, and use it to refactor my higher dimension code instead of templating the dimensionality.
It might have been better if I called it the Geometry Concepts Library, since the term template is too *ahem* generic.
I'll refrain on commenting on actual concept classes before I see any real code. Seems like an interesting concept; pun intentional, but I won't really know unless I see it and get to know the pros and cons of such an approach. I still doubt the inheritance approach, fwiw. Regards, -- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net