Lovely little discussion which would be great for beginning OO programmers to see. The question of whether to return 0 for an empty collection is interesting. While other things can be summed, we tend to think of sums returning numbers. In that sense, 0 is a great default return. On the other hand, having a specific object for a generic sum function is problematic (+1). There is a real tension and that would be a great discussion for people to have. Either way, the need for sumIfEmpty: is obvious.
Cheers, Jeff On Tue, Dec 1, 2015 at 11:19 AM Ben Coman <[email protected]> wrote: > On Tue, Dec 1, 2015 at 10:24 PM, Sven Van Caekenberghe <[email protected]> > wrote: > > Doru, > > > >> On 01 Dec 2015, at 15:11, Tudor Girba <[email protected]> wrote: > >> > >> Hi, > >> > >>> On Dec 1, 2015, at 12:52 PM, Sven Van Caekenberghe <[email protected]> > wrote: > >>> > >>> > >>>> On 01 Dec 2015, at 12:45, Stephan Eggermont <[email protected]> wrote: > >>>> > >>>> On 01-12-15 11:46, Sven Van Caekenberghe wrote: > >>>>> The basic question for me is, what should > >>>>> > >>>>> #() sum > >>>>> > >>>>> return. Right now, it is an error, I would very much like that for > this common case the result would be 0. There is a lot of power (easy of > use) in a unary selector, we should not destroy that with semantics that > force a test before using it. > >>>> > >>>> I like the error, it aligns with most of our collection protocol. > >>> > >>> I hate the error, a lot ;-) > >>> > >>>> It shows the need for #sum:ifEmpty: though > >>> > >>> Yes, as long as #() sum == 0 > >> > >> That won’t work :). > > > > Why ? Please explain. > > > >>> I want the simplest case to be simple, having a non-0 default is a > special case IMHO > >> > >> That is why you have sumNumbers:. We could also add > Collection>>sumNumbers. > >> > >> We had this discussion at length before Pharo 4, and this is when we > agreed to add sumNumbers: and let sum: be generic (like the name says it > should be) and not assume that it should work with Numbers. > > > > It is not about numbers or not, you are still using #+ in your generic > case, that is numeric in my book. It is about the zero element and how to > deal with an empty collection. > > > > The current solution, which was indeed recently added, leaves the > problem of what to do with an empty collection. There is no general > solution, you have to specify a zero element. > > > > But for most people in most cases that will be effectively 0, so lets > make the unary #sum respect that. (And unary #sum will also work for > non-empty non-zero based objects). The less common case can then use the > longer message. > > https://en.wikipedia.org/wiki/Empty_sum > >
