I think you're assuming that when I said "polymorphism", I meant "inheritance and virtual functions", but "polymorphism" just means having one piece of code operate on different kinds of data. Templates are a kind of polymorphism, and that's what I'm referring to.
In the general C++ community, there is a sharp distinction between run-time and compile-time polymorphism, due to the 'zero-overhead' philosophy of C++, (ie. you don't pay for what you don't absolutely _have_ to pay for). Therefore, unqualified use of the term 'polymorphism' is normally assumed to mean run-time polymophism (simply because that was added to C++ first), although you are correct in your usage of it otherwise. The 'safe' term to use in this case is 'generic' code. Just FYI.
I'm fully aware of the distinction between compile-time and run-time polymorphism, but the notion that 'polymorphism' is assumed to mean 'run-time' is new to me (FWIW, Stroustrup suggests 'polymorphism' as a general term for both kinds). In what sense is 'generic' a safe term? I had always thought 'generic' referred specifically to compile-time polymorphism (Googling for C++ generic programming seems to back this up), but I was trying to talk about polymorphism as a general concept, apart from whether it was implemented at compile-time or run-time. If you're not saying 'generic' fills that need, what word should I have used?
In other words, can you give an example of how you see this library being used, in a way that wouldn't be possible (or easy) without templates?
consider a function that *someone* will need to use, that doesn't depend on the representation of the data:
// where GraphContext is a TwoDimContainer with a value_type // convertable to PixelRepr template <class PixelRepr, class GraphContext> void resample(const GraphContext& from, GraphContext& to) { // ... // Dumb aliasing resampling to[x][y] = from[x*x_scale][y*y_scale]; // ... }
But this function doesn't really use the proposed library, or need it. All it requires is that PixelRepr be assignable; it doesn't even have to be a color, much less a color answering to the proposed interface.