Re: [boost] matrix and vector iterators

From: Andrew Lumsdaine (lums_at_[hidden])
Date: 2001-06-11 20:56:52

> >   *i  ??    // returns a matrix or vector element object.
> >   value(i)  // return the element value
> >   row(i)    // returns the row index
> >   column(i) // return the column index
> >   index(i)  // return the index (for vectors)
>
> Yes, I like this.

One thing Jeremy and I had tossed around some time ago while trying to get a
handle on what is a matrix is that a matrix could be viewed as a
doubly-indexed associative container.  If this seems like an interesting or
reasonable view of a matrix, then the iterator interface might look
something like std::map, but in this case the value type would be a triple
(key1, key2, value) instead of a pair.  The tuple library might have some
bearing on the interface in this case.

So here is a question.  Are the following semantically equivalent (is the
difference only syntax)?  Is there any reason to choose one over the other?

*i.first
row(*i)
row(i)

*i.second
col(*i)
col(i)

*i.third
val(*i)
val(i)

I think the third option (row(i), col(i), val(i)) makes for the more general
case of a triple, but perhaps it would be too general?

Again, it might be interesting to throw some algorithms around to see if
anything interesting falls out in comparing and contrasting these.