> On 4 Nov 2019, at 07:52, Akim Demaille <a...@lrde.epita.fr> wrote: > >> Le 4 nov. 2019 à 05:27, Matthew Fernandez <matthew.fernan...@gmail.com> a >> écrit : >> >> I recently had a use case for comparing source positions coming out of a C++ >> Bison-produced parser. While operator== and operator!= are implemented on >> the position class [0], the ordering operators (<, <=, >, >=) are not. It >> was relatively straightforward to implement these myself, but I was >> wondering if these were of wider use and should live upstream in Bison’s >> position implementation. Perhaps there is some history behind this or some >> deliberate omission of these operators? Just wanted to ask if there’s a >> reason these don’t already exist before thinking about posting a patch. I’m >> not subscribed to the list, so please CC me in replies. > > The semantics for line and columns are quite clear, so comparing Positions in > the same file is quite well defined. > > But what should you do when the files are different? (And Locations are > intervals, so there's no way to compare them totally in a natural order.) > > What we can do, though, is offer implementations for std::less, that would > blindly apply the lexicographic order in both cases. > > But the case of file names remains troublesome: should we compare the pointer > addresses (super fast, but non deterministic) or the pointees (super slow, > but deterministic)?
As it is not semantically well defined, but that one might want a total order for use in types like std::map, a pointer comparison might be used. Also containers like std::unordered_set have a total order through the iterators, so it fits with C++ paradigms, I would think.
