implementazione safe_ptr

Question

Sto provando ad implementare una versione sicura di std :: shared_ptr, chiamata "safe_ptr" che garantisce "non-nullness".

MODIFICA: domanda rimossa. Vedi modifica se interessati. Pubblicazione della soluzione finale a chiunque sia interessato:

Questo codice è ora ospitato su google code.

#pragma once 

#include <memory> 
#include <type_traits> 
#include <exception> 

template<typename T> 
class safe_ptr 
{ 
    template <typename> friend class safe_ptr; 
public: 
    typedef T element_type; 

    safe_ptr() : impl_(std::make_shared<T>()){} 

    safe_ptr(const safe_ptr<T>& other) : impl_(other.impl_){} 

    template<typename U> 
    safe_ptr(const safe_ptr<U>& other, typename std::enable_if<std::is_convertible<U*, T*>::value, void*>::type = 0) : impl_(other.impl_){} 

    template<typename U>  
    safe_ptr(const U& impl, typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, T*>::value, void>::type* = 0) 
     : impl_(std::make_shared<U>(impl)) {} 

    template<typename U, typename D>   
    safe_ptr(const U& impl, D dtor, typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, T*>::value, void>::type* = 0) 
     : impl_(new U(impl), dtor) {} 

    template<typename U>  
    safe_ptr(U&& impl, typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, T*>::value, void>::type* = 0) 
     : impl_(std::make_shared<U>(std::forward<U>(impl))) {} 

    template<typename U, typename D>  
    safe_ptr(U&& impl, D dtor, typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, T*>::value, void>::type* = 0) 
     : impl_(new U(std::forward<U>(impl)), dtor) {} 

    template<typename U>  
    explicit safe_ptr(const std::shared_ptr<U>& impl, typename std::enable_if<std::is_convertible<U*, T*>::value, void*>::type = 0) : impl_(impl) 
    { 
     if(!impl_) 
      throw std::invalid_argument("impl"); 
    } 

    template<typename U>  
    explicit safe_ptr(std::shared_ptr<U>&& impl, typename std::enable_if<std::is_convertible<U*, T*>::value, void*>::type = 0) : impl_(std::move(impl)) 
    { 
     if(!impl_) 
      throw std::invalid_argument("impl"); 
    } 

    template<typename U>  
    explicit safe_ptr(U* impl, typename std::enable_if<std::is_convertible<U*, T*>::value, void*>::type = 0) : impl_(impl) 
    { 
     if(!impl_) 
      throw std::invalid_argument("impl"); 
    } 

    template<typename U, typename D>  
    explicit safe_ptr(U* impl, D dtor, typename std::enable_if<std::is_convertible<U*, T*>::value, void*>::type = 0) : impl_(impl, dtor) 
    { 
     if(!impl_) 
      throw std::invalid_argument("impl"); 
    } 

    template<typename U> 
    typename std::enable_if<std::is_convertible<U*, T*>::value, safe_ptr<T>&>::type 
    operator=(const safe_ptr<U>& other) 
    { 
     safe_ptr<T> temp(other); 
     temp.swap(*this); 
     return *this; 
    } 

    template <typename U> 
    typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, T*>::value, safe_ptr<T>&>::type 
    operator=(U&& impl) 
    { 
     safe_ptr<T> temp(std::forward<T>(impl)); 
     temp.swap(*this); 
     return *this; 
    } 

    T& operator*() const { return *impl_.get();} 

    T* operator->() const { return impl_.get();} 

    T* get() const { return impl_.get();} 

    bool unique() const { return impl_.unique();} 

    long use_count() const { return impl_.use_count();} 

    void swap(safe_ptr& other) { impl_.swap(other.impl_); } 

    operator std::shared_ptr<T>() const { return impl_;} 

    template<class U> 
    bool owner_before(const safe_ptr<T>& ptr){ return impl_.owner_before(ptr.impl_); } 

    template<class U> 
    bool owner_before(const std::shared_ptr<U>& ptr){ return impl_.owner_before(ptr); } 

    template<class D, class U> 
    D* get_deleter(safe_ptr<U> const& ptr) { return impl_.get_deleter(); } 

private:  
    std::shared_ptr<T> impl_; 
}; 

template<class T, class U> 
bool operator==(const safe_ptr<T>& a, const safe_ptr<U>& b) 
{ 
    return a.get() == b.get(); 
} 

template<class T, class U> 
bool operator!=(const safe_ptr<T>& a, const safe_ptr<U>& b) 
{ 
    return a.get() != b.get(); 
} 

template<class T, class U> 
bool operator<(const safe_ptr<T>& a, const safe_ptr<U>& b) 
{ 
    return a.get() < b.get(); 
} 

template<class T, class U> 
bool operator>(const safe_ptr<T>& a, const safe_ptr<U>& b) 
{ 
    return a.get() > b.get(); 
} 

template<class T, class U> 
bool operator>=(const safe_ptr<T>& a, const safe_ptr<U>& b) 
{ 
    return a.get() >= b.get(); 
} 

template<class T, class U> 
bool operator<=(const safe_ptr<T>& a, const safe_ptr<U>& b) 
{ 
    return a.get() <= b.get(); 
} 

template<class E, class T, class U> 
std::basic_ostream<E, T>& operator<<(std::basic_ostream<E, T>& out, const safe_ptr<U>& p) 
{ 
    return out << p.get(); 
} 

template<class T> 
void swap(safe_ptr<T>& a, safe_ptr<T>& b) 
{ 
    a.swap(b); 
} 

template<class T> 
T* get_pointer(safe_ptr<T> const& p) 
{ 
    return p.get(); 
} 

template <class T, class U> 
safe_ptr<T> static_pointer_cast(const safe_ptr<U>& p) 
{ 
    return safe_ptr<T>(std::static_pointer_cast<T>(std::shared_ptr<U>(p))); 
} 

template <class T, class U> 
safe_ptr<T> const_pointer_cast(const safe_ptr<U>& p) 
{ 
    return safe_ptr<T>(std::const_pointer_cast<T>(std::shared_ptr<U>(p))); 
} 

template <class T, class U> 
safe_ptr<T> dynamic_pointer_cast(const safe_ptr<U>& p) 
{ 
    auto temp = std::dynamic_pointer_cast<T>(std::shared_ptr<U>(p)); 
    if(!temp) 
     throw std::bad_cast(); 
    return safe_ptr<T>(temp); 
} 

template<typename T> 
safe_ptr<T> make_safe() 
{ 
    return safe_ptr<T>(); 
} 

template<typename T, typename P0> 
safe_ptr<T> make_safe(P0&& p0) 
{ 
    return safe_ptr<T>(std::make_shared<T>(std::forward<P0>(p0))); 
} 

template<typename T, typename P0, typename P1> 
safe_ptr<T> make_safe(P0&& p0, P1&& p1) 
{ 
    return safe_ptr<T>(std::make_shared<T>(std::forward<P0>(p0), std::forward<P1>(p1))); 
} 

template<typename T, typename P0, typename P1, typename P2> 
safe_ptr<T> make_safe(P0&& p0, P1&& p1, P2&& p2) 
{ 
    return safe_ptr<T>(std::make_shared<T>(std::forward<P0>(p0), std::forward<P1>(p1), std::forward<P2>(p2))); 
} 

template<typename T, typename P0, typename P1, typename P2, typename P3> 
safe_ptr<T> make_safe(P0&& p0, P1&& p1, P2&& p2, P3&& p3) 
{ 
    return safe_ptr<T>(std::make_shared<T>(std::forward<P0>(p0), std::forward<P1>(p1), std::forward<P2>(p2), std::forward<P3>(p3))); 
} 

template<typename T, typename P0, typename P1, typename P2, typename P3, typename P4> 
safe_ptr<T> make_safe(P0&& p0, P1&& p1, P2&& p2, P3&& p3, P4&&) 
{ 
    return safe_ptr<T>(std::make_shared<T>(std::forward<P0>(p0), std::forward<P1>(p1), std::forward<P2>(p2), std::forward<P3>(p3), std::forward<P3>(p4))); 
} 

Answer 1

Hai ottenuto gli argomenti a is_convertible indietro. Si vuole controllare Y*-T* che si esprime come:

std::is_convertible<Y*, T*> 

Per quanto riguarda la modifica: sì, avete bisogno di un amico dichiarazione

// Within the body of the class 
template <typename> friend class safe_ptr; // the syntax is peculiar... 

Inoltre, si potrebbe voler fornire un costruttore predefinito per safe_ptr, quale naturalmente predefinito costruisce l'oggetto. Avevo dimenticato di invocare il costruttore predefinito dell'oggetto indicato nella mia risposta alla domanda precedente :)

Answer 2

Penso che si sta utilizzando is_convertible backwarks. Prova

template<typename Y> 
safe_ptr(const safe_ptr<Y>& other, typename std::enable_if<std::is_convertible<Y*, T*>::value, void*>::type = 0) : impl_(other.impl_){} 

Answer 3

Per l'accesso del membro privato impl_, è necessario fare amicizia con diverse istanze del modello safe_ptr.

template <class Y> friend class safe_ptr; 

Answer 4

template<class Y> friend class safe_ptr;