----- Original Message -----
I've been mulling this over, and I have an idea that is starting to grow on me.
What if we left insertion() and deletion() (and substitution) as-is: they continue to receive individual sequence elements, and operation scores. But we *do* modify the equality() method to take two ranges, in the manner you suggested above. It would introduce an asymmetry of equality() with respect to the other methods, but I think there are some real arguments for it:
[snip]
*) Runs of 'equal' dominate the script in most larger-scale applications of interest. Actual insertions, deletions, etc, are relatively small.
I can't agree with that; for me, a common case is where the two inputs are entirely different.
Something of a tangent, but I'm curious how that works for you. When two strings are entirely different, the algorithm cost is O(NxM). On larger data, say a million elements, that's terabytes of working data, and tera-ops.
Here's another possibility: don't pass ranges, but do pass iterators:
struct output {
ITER pending; enum ... last_action; void insertion(ITER i, int) { if (last_action != insert) { do_something_with(pending,i); pending = i; last_action = insert; } } // etc.
};
The point here is that I just need to store the iterator for the start of the range until I get a different action; in contrast, if the value is passed I need to accumulate a copy of the range.
That seems promising. It makes it straightforward to handle the script data either as it appears, or save up an iterator range. I could use a similar variation on the 'diff' example, and not bother to copy the file data, just refer back to the original for output.