[GiNaC-devel] Subclassing symbol

[Jan Rheinländer]

Hi,

something must be wrong with my subclass, but I don't understand it. I
subclassed symbol to get a non-commutative version:

---------- HEADER  --------------
#include <ginac/symbol.h>

namespace GiNaC {

class ncsymbol: public symbol {
public:
    ncsymbol(const symbol& s);
    explicit ncsymbol(const std::string & initname);
    ncsymbol(const std::string & initname, const std::string & texname);
       
     unsigned return_type() const { return
return_types::noncommutative_composite; }
};
GINAC_DECLARE_UNARCHIVER(ncsymbol);
}

---------- IMPLEMENTATION -------------
#include <ginac/ginac.h>

namespace GiNaC {

// non-commutative symbol
ncsymbol::ncsymbol() : symbol() { }

ncsymbol::ncsymbol(const symbol& s) : symbol(s) { }

ncsymbol::ncsymbol(const std::string & initname) : symbol(initname) { }

ncsymbol::ncsymbol(const std::string & initname, const std::string &
texname) : symbol(initname, texname) { }

GINAC_BIND_UNARCHIVER(ncsymbol);
--------------------------------------

But when I execute the following code the program crashes when printing x:

symbol x("x");
x = ncsymbol("y");
std::cout << x << std::endl;

It does not crash if I print ncsymbol("y") directly (without assigning
it to x first). Can anybody explain why? Did I forget to implement an
essential method?

Thanks!
Jan