language: C++ 4.7.2 (gcc-4.7.2)
date: 524 days 0 hours ago
link:
visibility: public 
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struct base {};  //In actual code, this is a template struct that holds data
template<class category, class valuetype>  
    struct any;  //In actual code, this is abstract base struct
template<class basetype, class category, class valuetype> 
    struct from; //In actual code, this is function definitions of any
 
template<class valuetype>
struct any<void,valuetype>
{ void a() {} };
template<class category, class valuetype>  
struct any
    : public any<void,valuetype> //commenting this line makes it compile
{ void b() {} };        
 
template<class basetype, class valuetype>
struct from<basetype,void,valuetype>
    : public base  //commenting out _either_ of these makes it compile
    , public any<void,valuetype>
{ void c() {} };
 
int main() {
    from<int, void, char> a;
    a.a();
    a.c();
    any<int, char> b;
    b.a();
    b.b();
    return 0;
}