#include <set>
struct S {
  template<class T, class U>
  bool operator()(T& a, U& b) const { return a < b; }
};
struct Man {
  int id_;
  auto operator<=>(const Man&) const = default;
};
struct ManComp {
  bool operator()(const Man &l,const int& r)const
  {
    return l.id_ < r;
  }
  bool operator()(const int& l, const Man& r)const
  {
    return l < r.id_;
  }
  bool operator()(const Man& l, const Man& r)const
  {
    return l.id_ < r.id_;
  }
};
void f() {
  std::set<Man,ManComp> m;
  m.find(11);//将报错
}
void g()
{
std::set<Man,folly::transparent<ManComp>> m;
  m.find(11);
}