Date: Sun, 8 Mar 2020 19:36:52 -0400

... And only the classes with the proper declarations would take

advantage of the generic template 'this':

advantage of the generic template 'this':

-- *Phil Bouchard* Founder C.: (819) 328-4743 Fornux Logo <http://www.fornux.com> On 3/8/20 7:34 PM, Phil Bouchard wrote: > > What I have in mind is to clean up the dispatch fiasco that is done > with either the constructors or the cast operator right now. > Conversions, comparisons, ... should be simplified as well. For example: > > struct X > > { > > int value; > > > template <typename T> > > X(T const & T); > > template <typename T> > > operator T (); > > }; > > struct Y > > { > > int value; > > > template <typename T> > > Y(T const & T); > > template <typename T> > > operator T (); > > }; > > template <typename Class, typename T> > > inline Class::operator T () { return T(* this); } // generic > constructor wrapper > > template <typename Class, typename T> > > inline Class::Class(T const &t) { value = t.value; } // cast > operation really done here > > > And normal specializations here: > > template <typename T> > > inline X::X(T const &t) { value = t.value; } // specialized cast > operation done here > > > Also if we had a way to iterate all members (which would be another > important proposal) then we could also have a generic "operator <<" as > well: > > template <typename Class> > > ostream & Class::operator << (ostream & out) > > { > > for (member_iterator<Class> i = > member_iterator<Class>::begin(); i != member_iterator<Class>::end(); ++ i) > > { > > if (i != member_iterator<Class>::begin()) > > out << ", "; > > out << this->*i; > > } > > return out; > > } > > The aforementioned should also remove the need for these global friend > function overloads. > > > -- > > *Phil Bouchard* > Founder > C.: (819) 328-4743 > > Fornux Logo <http://www.fornux.com> > > > On 3/8/20 6:03 PM, Jake Arkinstall wrote: >> For me, this approach has some merits, but this particular example is >> something that, to me, makes much more sense as a free function. >> >> Do you have further examples? >> >> On Sun, 8 Mar 2020, 21:55 Phil Bouchard via Std-Proposals, >> <std-proposals_at_[hidden] >> <mailto:std-proposals_at_[hidden]>> wrote: >> >> Well I believe a proposal should be open for debate, just like a >> thesis. >> >> We both agree these overloads should be simplified but we >> disagree on the syntax. >> >> I saw the recursive lambda thing and I think I already talked to >> you before regarding CV overloads but we were proposing the >> following syntax: >> >> struct A >> >> { >> >> template <bool BC> >> >> void foo() bool<BC> >> >> { >> >> } >> >> }; >> >> And regarding the this generic overloading I still believe the >> following syntax is cleaner: >> >> struct A >> >> { >> >> template <typename T> >> >> bool compare(T const &); >> >> }; >> >> template <typename C, typename T> >> >> void C::compare(C const &) >> >> { >> >> ... >> >> } >> >> Because with your syntax I could technically reassign "self": >> >> struct A >> >> { >> >> template <typename C, typename T> >> >> bool compare(this C & c, T const &); >> >> }; >> >> template <typename C, typename T> >> >> bool C::compare(this C & c, T const &) // redundant C here >> >> { >> >> static C sc = C(); >> >> c = sc; // in theory we could do this unless you patch >> the compilers with a new error for that specific case >> >> } >> >> >> -- >> >> *Phil Bouchard* >> Founder >> C.: (819) 328-4743 >> >> Fornux Logo <http://www.fornux.com> >> >> >> On 3/8/20 5:37 AM, Gašper Ažman wrote: >>> I meant that you should consider the incremental value of your >>> proposal over p0847, which is on track for c++23 unless serious >>> issues crop up >>> >>> On Sat, Mar 7, 2020, 19:04 Phil Bouchard <phil_at_[hidden] >>> <mailto:phil_at_[hidden]>> wrote: >>> >>> The syntaxes are way different: >>> >>> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p0847r4.html >>> >>> In your case the compiler will have to change all of its >>> rules for the number of parameters "operator" overloads. For >>> example: >>> >>> struct A >>> >>> { >>> >>> int value; >>> >>> ... >>> >>> template <typename Self> >>> >>> bool operator < (this Self && self, A const & a) // >>> 2 parameters... ok >>> >>> { >>> >>> return self.value < a.value; >>> >>> } >>> >>> >>> bool operator < (A const & a) // 1 parameter... ok >>> >>> { >>> >>> return value < a.value; >>> >>> } >>> >>> }; >>> >>> >>> -- >>> >>> *Phil Bouchard* >>> Founder >>> C.: (819) 328-4743 >>> >>> Fornux Logo <http://www.fornux.com> >>> >>> >>> On 3/7/20 1:35 PM, Gašper Ažman wrote: >>>> P0847 >>>> >>>> On Sat, Mar 7, 2020, 18:33 Phil Bouchard via Std-Proposals >>>> <std-proposals_at_[hidden] >>>> <mailto:std-proposals_at_[hidden]>> wrote: >>>> >>>> Alright, I'm pretty sure this is not implemented yet. >>>> Suppose you have: >>>> >>>> struct A >>>> >>>> { >>>> >>>> int value; >>>> >>>> ... >>>> >>>> template <typename T> >>>> >>>> int compare(T const & t) const; >>>> >>>> } >>>> >>>> >>>> struct B >>>> >>>> { >>>> >>>> int value; >>>> >>>> ... >>>> >>>> template <typename T> >>>> >>>> int compare(T const & t) const; >>>> >>>> } >>>> >>>> >>>> Then a generic way to define the same functionality for >>>> all classes would be to have a "template 'this'": >>>> >>>> template <typename C, typename T> >>>> >>>> inline int C::compare(T const & t) const >>>> >>>> { >>>> >>>> return value == t.value ? 0 : value < >>>> t.value ? -1 : 1; >>>> >>>> } >>>> >>>> >>>> (Please include my email address in your replies) >>>> >>>> >>>> -- >>>> >>>> *Phil Bouchard* >>>> Founder >>>> C.: (819) 328-4743 >>>> >>>> Fornux Logo <http://www.fornux.com> >>>> -- >>>> Std-Proposals mailing list >>>> Std-Proposals_at_[hidden] >>>> <mailto:Std-Proposals_at_[hidden]> >>>> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals >>>> >> -- >> Std-Proposals mailing list >> Std-Proposals_at_[hidden] >> <mailto:Std-Proposals_at_[hidden]> >> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals >>

Received on 2020-03-08 18:39:40