std::owner_less::operator()(C++11)

// shared_ptr特殊化版
bool operator()(const shared_ptr<T>& a, const shared_ptr<T>& b) const;          // (1) C++11
bool operator()(const shared_ptr<T>& a, const shared_ptr<T>& b) const noexcept; // (1) C++17

bool operator()(const shared_ptr<T>& a, const weak_ptr<T>& b) const;            // (2) C++11
bool operator()(const shared_ptr<T>& a, const weak_ptr<T>& b) const noexcept;   // (2) C++17

bool operator()(const weak_ptr<T>& a, const shared_ptr<T>& b) const;            // (3) C++11
bool operator()(const weak_ptr<T>& a, const shared_ptr<T>& b) const noexcept;   // (3) C++17

// weak_ptr特殊化版
bool operator()(const weak_ptr<T>& a, const weak_ptr<T>& b) const;              // (4) C++11
bool operator()(const weak_ptr<T>& a, const weak_ptr<T>& b) const noexcept;     // (4) C++17

bool operator()(const shared_ptr<T>& a, const weak_ptr<T>& b) const;            // (5) C++11
bool operator()(const shared_ptr<T>& a, const weak_ptr<T>& b) const noexcept;   // (5) C++17

bool operator()(const weak_ptr<T>& a, const shared_ptr<T>& b) const;            // (6) C++11
bool operator()(const weak_ptr<T>& a, const shared_ptr<T>& b) const noexcept;   // (6) C++17

// void特殊化版
template<class T, class U>
bool operator()(const shared_ptr<T>&, const shared_ptr<U>&) const noexcept;     // (7) C++17

template<class T, class U>
bool operator()(const shared_ptr<T>&, const weak_ptr<U>&) const noexcept;       // (8) C++17

template<class T, class U>
bool operator()(const weak_ptr<T>&, const shared_ptr<U>&) const noexcept;       // (9) C++17

template<class T, class U>
bool operator()(const weak_ptr<T>&, const weak_ptr<U>&) const noexcept;         // (10) C++17

a.owner_before(b)