On 06/12/01 14:50, David Abrahams wrote:
----- Original Message ----- From: "Larry Evans" <jcampbell3@prodigy.net>
David Abrahams wrote:
One problem with this is that it requires much more of the iterator in some cases than it otherwise might. In an array stored as vectors of vectors of... vectors, each iterator would need to have references to all of the containing vectors.
Couldn't the iterator just contain a vector of indices of length == rank, and a pointer to the vector of vectors of... vectors (VofV), and then just index into the VofV with the vector of indices.
When you start talking about iterators containing vectors, I get worried.
I guess bad thing about that is that it takes longer.
That's putting it mildly. Iterators should be lightweight.
-Dave
Another type of iterator which essentially flattens a multi-dimensional array and *may* be more lightweight is implemented here: http://svn.boost.org/svn/boost/sandbox/variadic_templates/sandbox/stepper/bo... and demonstrated here: http://svn.boost.org/svn/boost/sandbox/variadic_templates/sandbox/stepper/li... A more realistic demonstration is in the Partial Differential Equation example here: http://svn.boost.org/svn/boost/sandbox/variadic_templates/sandbox/stepper/li... which uses an axes rotation feature that, IIUC, was requested by Petros here: http://article.gmane.org/gmane.comp.lib.boost.user/68017 Its also used here: http://svn.boost.org/svn/boost/sandbox/variadic_templates/sandbox/stepper/li... which is probably a bit easier to follow than the array_dyn.diff_pde.cpp one ;) I've done no benchmarks; hence, I can't say how lightweight it is; however, since all it does is keep a stack of indices in a data structure instead of on the stack, I would think it wouldn't be that much more heavyweight than simply a nested for loop nested N deep where N is the array dimensionality. BTW, Petros, in a private email to me, has indicated he has some other method for solving the rotated axes problem; however, I've no idea if that's more or less lightweight than this one. -regards, Larry I've run no benchmarks to show how lightweight it may be. Petros, in a private email to me, says he has another way of