Christopher Harvey skrev:
This is a pretty simple question, so I'll just go ahead and paste the test case i wrote. The compile errors are right below it.
(boost version: 1.34.1-r2)
#include <utility> #include
class Filter { public: virtual void blah() const = 0; };
class SpecificFilter : public Filter { public:
SpecificFilter() : Filter() {} void blah() const { } };
int main() { boost::ptr_map
map; map[0].blah(); }
/usr/include/boost/ptr_container/ptr_map_adapter.hpp:168: error: cannot allocate an object of abstract type 'Filter' main.cc:5: note: because the following virtual functions are pure within 'Filter': main.cc:7: note: virtual void Filter::blah() const
I'm surprised it's not happy about the fact that blah is pure virtual because this is a pointer container so I thought that wouldn't be a problem.
No matter what, then you can't create an object of abstract type. operator[]() needs to create a default argument.
Side note: What happens when I try to access an element that doesn't exist, and what happens when I insert two elements with the same key?
with operator[](), a default constructed element is inserted. With at(key), an exception is thrown. As for double insertions, then the same happens as in a normal map. -Thorsten