#include <unordered_set>

using namespace std;

struct MyType {
    int val;
};

struct MyTypeEquals {
    using is_transparent = void;
    bool operator()(MyType const& l, MyType const& r) const {
        return l.val == r.val;
    }
    bool operator()(int const l, MyType const& r) const {
        return l == r.val;
    }
    bool operator()(MyType const& l, int const r) const {
        return l.val == r;
    }
};

struct MyTypeHash {
    using transparent_key_equal = MyTypeEquals;

    std::size_t operator()(MyType const& s) const {
        return hash<int>()(s.val);
    }

    std::size_t operator()(int const& s) const {
        return hash<int>()(s);
    }
};

int main()
{
    unordered_set<MyType, MyTypeHash, MyTypeEquals> mytype_set;
    mytype_set.insert(MyType{1});
    mytype_set.equal_range(1);
    // As of 2020-02-14 this gives a compile error in GCC 10.0.1.20200 with -std=c++2a:
    // no known conversion for argument 1 from 'int' to 'const key_type&' {aka 'const MyType&'}
    // as
}