Dear Vladimir, Thanks very much for the quick reply! Indeed, when I remove the calchash method, I get the expected result. So when writting to an archive, GiNaC will use the hash internally, and I still have a question, why does the first console output give the result: "read: {k1^2,k2^2}”? Thanks again! Best regards! Feng 在 2021年12月18日 19:10，Vladimir V. Kisil<V.Kisil@leeds.ac.uk> 写道：

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On Sat, 18 Dec 2021 16:22:22 +0800, Feng Feng <f.feng@outlook.com> said: FF> I got a strange behaviour while implementing the archive in FF> user-defined class, to make the behaviour more explicitly, let If you will delete the method Symbol::calchash() from your class you will get the expected behaviour. -- Vladimir V. Kisil http://www.maths.leeds.ac.uk/~kisilv/ Book: Geometry of Mobius Maps https://doi.org/10.1142/p835 Soft: Geometry of cycles http://moebinv.sourceforge.net/ Jupyter notebooks: https://github.com/vvkisil?tab=repositories >>>>> On Sat, 18 Dec 2021 16:22:22 +0800, Feng Feng <f.feng@outlook.com> said: FF> Dear all, FF> I got a strange behaviour while implementing the archive in FF> user-defined class, to make the behaviour more explicitly, let FF> me post the C++ code here: FF> #include <ginac/ginac.h> #include <fstream> FF> using namespace GiNaC; using namespace std; FF> class Symbol : public symbol { FF> GINAC_DECLARE_REGISTERED_CLASS(Symbol, symbol) public: FF> Symbol(const string &s); void archive(archive_node & n) const FF> override; void read_archive(const archive_node& n, lst& sym_lst) FF> override; unsigned calchash() const override; }; FF> GINAC_DECLARE_UNARCHIVER(Symbol); FF> GINAC_IMPLEMENT_REGISTERED_CLASS(Symbol, symbol) FF> GINAC_BIND_UNARCHIVER(Symbol); FF> const symbol & get_symbol(const string & s) { static map<string, FF> symbol> dict; if (dict.find(s) == dict.end()) dict[s] = FF> symbol(s); return dict[s]; } FF> Symbol::Symbol() { } Symbol::Symbol(const string &s) : FF> symbol(get_symbol(s)) { } int Symbol::compare_same_type(const FF> basic &other) const { const Symbol &o = static_cast<const Symbol FF> &>(other); int ret = get_name().compare(o.get_name()); FF> if(ret==0) return 0; else if(ret<0) return -1; else return 1; } FF> void Symbol::archive(archive_node & n) const { FF> inherited::archive(n); } FF> void Symbol::read_archive(const archive_node& n, lst& sym_lst) { FF> inherited::read_archive(n, sym_lst); *this = Symbol(get_name()); FF> } FF> unsigned Symbol::calchash() const { static auto hash = FF> symbol("_").gethash(); return hash; } FF> int main() { Symbol k1("k1"), k2("k2"); auto garfn = "tmp.gar"; FF> { archive ar; ex val = lst{ k1*k1, k2*k2 }; FF> ar.archive_ex(val, "key"); ofstream out(garfn); out << ar; FF> out.close(); cout << "writed: " << val << endl; } { archive ar; FF> ifstream in(garfn); in >> ar; in.close(); auto val = FF> ar.unarchive_ex(lst{}, "key"); cout << "read: " << val << endl; FF> } // console output is // writed: {k1^2,k2^2} // read: FF> {k1^2,k2^2} FF> { archive ar; ex val = lst{ k1*k1==0, k2*k2==0 }; FF> ar.archive_ex(val, "key"); ofstream out(garfn); out << ar; FF> out.close(); cout << "writed: " << val << endl; } { archive ar; FF> ifstream in(garfn); in >> ar; in.close(); auto val = FF> ar.unarchive_ex(lst{}, "key"); cout << "read: " << val << endl; FF> } // console output is // writed: {k1^2==0,k2^2==0} // read: FF> {k1^2==0,k1^2==0} // Note that the last line above, both items FF> are the same: k1^2==0 FF> return 0; } FF> Here I want to introduce a class Symbol, when one defines Symbol FF> a(“a”), b(“a”);, then a and b will be the same or equal, so I FF> override the method compare_same_type. FF> The last console output seems very strange to me, the both items FF> are the same, while the expected result is "read: FF> {k1^2==0,k2^2==0}”. FF> Thanks very much! FF> Best regards! Feng FF> ---------------------------------------------------- FF> Alternatives: FF> ---------------------------------------------------- FF> _______________________________________________ GiNaC-list FF> mailing list GiNaC-list@ginac.de FF> https://www.ginac.de/mailman/listinfo/ginac-list