#include <iostream>
#include <unordered_set>
#include <string>

namespace uset {
typedef struct PeopleInfo {
  std::string name;
  int age;
} PInfo, *PInfo_ptr;

typedef bool(*info_com)(const PInfo&, const PInfo&);
// std::function<bool(const PInfo&, const PInfo&)> info_com;

bool info_compare(const PInfo& left, const PInfo& right) {
  return left.age > right.age;
}

struct PeopleInfoCompare {
  bool operator()(const PInfo& left, const PInfo& right) const {
    return left.age > right.age;
  }
};
}  // end of namespace uset

namespace std {
  template <>
  struct hash<uset::PInfo> {
    size_t operator()(const uset::PInfo& self) const {
	  return std::hash<std::string>()(self.name) + std::hash<int>()(self.age);
	}
  };
}  // end of namespace std


int main()
{
  // std::hash<uset::PInfo> 类型， std::hash<uset::PInfo>()可调用对象
  std::unordered_set<uset::PInfo, std::hash<uset::PInfo>, uset::info_com> a(2, std::hash<uset::PInfo>(), &uset::info_compare);
  uset::PInfo obj1({"xiaoming", 18});
  a.insert(obj1);
  a.insert({"xiaohuang", 19});
  for (const auto& key : a) {
    std::cout << key.age << std::endl;
  }
  std::cout << "aaaa" << std::endl;
  std::unordered_set<uset::PInfo, std::hash<uset::PInfo>, uset::PeopleInfoCompare> b;
  b.insert({"xiaoming1", 18});
  b.insert({"xiaohuang1", 19});
  for (const auto& key : b) {
    std::cout << key.age << std::endl;
  }
  return 0;
}

结果：

19
18
aaaa
19
18