int already has an instance of Ord. SaltedOrd would be another one, thus non-coherence.
Geoffrey On Wed, Jan 7, 2015 at 5:59 PM, Keean Schupke <[email protected]> wrote: > Okay, I see what you are getting at now. I don't really see any problem with > the first C++ solution... How would non-coherent instances help? > > On 8 January 2015 at 01:24, Geoffrey Irving <[email protected]> wrote: >> >> On Wed, Jan 7, 2015 at 5:16 PM, Keean Schupke <[email protected]> wrote: >> > I'm probably being slow, but I don't see that. With sortBy you pass the >> > comparison function explicitly. With a 'view' the comparison function is >> > passed implicitly (by they type). That is the only difference. A view is >> > simply type that overrides the comparator. >> > >> > Where is the extra memory etc coming from? >> >> For concreteness, here's what it looks like in C++: >> >> template <class RandomAccessIterator> >> void sort (RandomAccessIterator first, RandomAccessIterator last); >> >> template <class RandomAccessIterator, class Compare> >> void sort (RandomAccessIterator first, RandomAccessIterator last, >> Compare comp); >> >> The first is sort, the second is sortBy. Say the comparison function >> looks like >> >> class SaltedCompare { >> HugeClass salt; >> bool operator()(int x, int y) const { return hash(salt,x) < >> hash(salt,y); } >> } >> >> where the salt is (for some reason) huge. In C++, we pass a single >> instance of SaltedCompare to the second version of sort, and the first >> two arguments can point directly into a flat array of ints. >> >> Instead, you propose making a SaltedInt type. At best, this would >> look something like >> >> class SaltedInt { >> HugeClass* salt; >> int x; >> bool operator<(...) { ... } >> } >> >> We either add another memory indirection or store a copy of HugeClass >> in every entry. In either case, we need to copy the array. >> >> Apologies if what I'm describing is different from the views you had in >> mind. >> >> Geoffrey >> _______________________________________________ >> bitc-dev mailing list >> [email protected] >> http://www.coyotos.org/mailman/listinfo/bitc-dev > > > > _______________________________________________ > bitc-dev mailing list > [email protected] > http://www.coyotos.org/mailman/listinfo/bitc-dev > _______________________________________________ bitc-dev mailing list [email protected] http://www.coyotos.org/mailman/listinfo/bitc-dev
