Question

I have an unordered_set of a class ActiveStatusEffect The set is declared as follows:

boost::unordered_set<StatusEffects::ActiveStatusEffect> ActiveStatusEffects;

ActiveStatusEffect is defined as follows:

class ActiveStatusEffect
    {
    public:
        StatusEffect* effect;
        int ReminaingTurns;
        bool operator<(const ActiveStatusEffect& ase) const
        {
            return *effect < *ase.effect;
        }
        bool operator>(const ActiveStatusEffect& ase) const
        {
            return *effect > *ase.effect;
        }
        bool operator==(const ActiveStatusEffect& ase) const
        {
            return *effect == *ase.effect;
        }
        bool operator!=(const ActiveStatusEffect& ase) const
        {
            return !((*this) == ase);
        }
    };

The comparison between StatusEffect’s is a comparison between a unique integer assinged to each instance of a status effect.

However, if I try to sort the effects like follows:

std::sort(statusSet.begin(), statusSet.end(), [](StatusEffects::ActiveStatusEffect const &se1, StatusEffects::ActiveStatusEffect const &se2){return se1.effect->GetPriority() < se2.effect->GetPriority();});

I get many errors in the algorithm header file such as

Error 198 error C2784:
‘_Base1::difference_type std::operator
-(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2>
&)’ : could not deduce template
argument for ‘const
std::_Revranit<_RanIt,_Base> &’ from
‘boost::unordered_detail::hash_const_iterator’ c:\program
files (x86)\microsoft visual studio
10.0\vc\include\algorithm 3806

Error 199 error C2784:
‘_Base1::difference_type std::operator
-(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2>
&)’ : could not deduce template
argument for ‘const
std::_Revranit<_RanIt,_Base> &’ from
‘boost::unordered_detail::hash_const_iterator’ c:\program
files (x86)\microsoft visual studio
10.0\vc\include\algorithm 3806

Why am I not able to sort the set? I’m quite certain this is something about unordered_set as removing attempts to sort or changing it to a vector does not generate errors.

Answer 1

boost::unordered_set<Foo> a;
a.insert(...);
...

std::set<Foo> b(a.begin(), a.end());

std::set<Foo> c;
std::copy(a.begin(), a.end(), std::inserter(c, c.end());

Voilà, a sorted set.