23.associative.stdcxx-16.cpp

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#include <set>
#include <map>
#include <cassert>
 
template <class T>
struct RuntimeCmp
{
    enum cmp_mode {normal, reverse};
 
    cmp_mode mode;
 
    RuntimeCmp (cmp_mode m = normal) : mode (m) { }
 
    bool operator() (const T& t1, const T& t2) const {
        return mode == normal ? t1 < t2 : t2 < t1;
    }
};
 
template <class T>
bool operator== (const RuntimeCmp <T>& lc, const RuntimeCmp <T>& rc) {
    return lc.mode == rc.mode;
}
 
typedef std::set <int, RuntimeCmp <int> > IntSet;
typedef std::map <int, int, RuntimeCmp <int> > IntMap;
 
int main ()
{
    RuntimeCmp <int> reverse_order (RuntimeCmp<int>::reverse);
 
    IntSet set1;
    IntSet set2 (reverse_order);
    set1 = set2;
    assert (set1.key_comp () == set2.key_comp ());
    assert (set1.value_comp () == set2.value_comp ());
 
    IntMap map1;
    IntMap map2 (reverse_order);
    map1 = map2;
    assert (map1.key_comp () == map2.key_comp ());
 
    return 0;
}