写道
RAII
https://en.cppreference.com/w/cpp/language/raii
https://en.cppreference.com/w/cpp/language/raii
写道
Object lifetime and resource management (RAII)
https://docs.microsoft.com/en-us/cpp/cpp/object-lifetime-and-resource-management-modern-cpp?view=msvc-170
https://docs.microsoft.com/en-us/cpp/cpp/object-lifetime-and-resource-management-modern-cpp?view=msvc-170
智能指针
C++提供了几种智能指针的实现，包括auto_ptr、unique_ptr、shared_ptr、weak_ptr，它们都是一些类模版。其中auto_ptr自C++11开始已经废弃。
C++的智能指针为指针（主要是对象资源）提供了一种有限的垃圾回收（garbage collection）功能。相较于其他高级语言的GC支持，C++智能指针提供的这种有限的垃圾回收实在是低级。
如下面的示例中，不管是auto_ptr、unique_ptr或者shared_ptr，都不能保证对象资源能够被正确的释放回收。
int *i = new int(100);
std::***_ptr<int> p1(i);
std::***_ptr<int> p2(i);
unique_ptr
unique_ptr定义如下：
template <class T, class D = default_delete<T>>
class unique_ptr
{
public:
typedef see below pointer;
typedef T element_type;
typedef D deleter_type;
// constructors
constexpr unique_ptr() noexcept;
explicit unique_ptr(pointer p) noexcept;
unique_ptr(pointer p, see below d1) noexcept;
unique_ptr(pointer p, see below d2) noexcept;
unique_ptr(unique_ptr&& u) noexcept;
unique_ptr(nullptr_t) noexcept : unique_ptr() { }
template <class U, class E>
unique_ptr(unique_ptr<U, E>&& u) noexcept;
template <class U>
unique_ptr(auto_ptr<U>&& u) noexcept;
// destructor
~unique_ptr();
// assignment
unique_ptr& operator=(unique_ptr&& u) noexcept;
template <class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
unique_ptr& operator=(nullptr_t) noexcept;
// observers
typename add_lvalue_reference<T>::type operator*() const;
pointer operator->() const noexcept;
pointer get() const noexcept;
deleter_type& get_deleter() noexcept;
const deleter_type& get_deleter() const noexcept;
explicit operator bool() const noexcept;
// modifiers
pointer release() noexcept;
void reset(pointer p = pointer()) noexcept;
void swap(unique_ptr& u) noexcept;
};
这里需要注意下几个typedef，element_type、deleter_type这两个还好理解，对应模板参数中的T、D。pointer的定义就不好理解了，除了知道pointer是一个定义的类型之外，“see below”是什么东西？typedef see below pointer;这样的typedef感觉就不是个正经typedef，而且pointer和“see below”还出现了好几次。
上面定义中的“see below”让人感觉一头雾水，包括C++标准中很有很多这样的“see below”，可以看下面的定义。
pointer
定义如下：
typedef typename __pointer_type<_Tp, deleter_type>::type pointer;
pointer的类型定义为__pointer_type<_Tp, deleter_type>中的type类型。
其中__pointer_type定义如下：
template <class _Tp, class _Dp>
struct __pointer_type
{
typedef typename __pointer_type_imp::__pointer_type<_Tp, typename remove_reference<_Dp>::type>::type type;
};
这里的type类型定义为__pointer_type_imp::__pointer_type<_Tp, typename remove_reference<_Dp>::type>中的type类型。
在__pointer_type_imp命名空间中，__pointer_type定义如下：
template <class _Tp, class _Dp, bool = __has_pointer_type<_Dp>::value>
struct __pointer_type
{
typedef typename _Dp::pointer type;
};
下面是__pointer_type的一个模板特化，__pointer_type_imp::__pointer_type<_Tp, typename remove_reference<_Dp>::type>中的type类型就是下面的特化中的type类型，而这个type的类型其实就是模板参数_Tp的指针类型。
template <class _Tp, class _Dp>
struct __pointer_type<_Tp, _Dp, false>
{
typedef _Tp* type;
};
根据上面的分析，unique_ptr中的pointer类型其实就是模板参数T的指针类型。即
typedef see below pointer;
等价于
typedef T* pointer;
根据下面的定义，
template <class _T1, class _T2>
class __compressed_pair
: private __libcpp_compressed_pair_imp<_T1, _T2>
{
typedef __libcpp_compressed_pair_imp<_T1, _T2> base;
public:
typedef typename base::_T1_param _T1_param;
typedef typename base::_T2_param _T2_param;
typedef typename base::_T1_reference _T1_reference;
typedef typename base::_T2_reference _T2_reference;
typedef typename base::_T1_const_reference _T1_const_reference;
typedef typename base::_T2_const_reference _T2_const_reference;
_LIBCPP_INLINE_VISIBILITY __compressed_pair() {}
_LIBCPP_INLINE_VISIBILITY explicit __compressed_pair(_T1_param __t1)
: base(_VSTD::forward<_T1_param>(__t1)) {}
_LIBCPP_INLINE_VISIBILITY explicit __compressed_pair(_T2_param __t2)
: base(_VSTD::forward<_T2_param>(__t2)) {}
_LIBCPP_INLINE_VISIBILITY __compressed_pair(_T1_param __t1, _T2_param __t2)
: base(_VSTD::forward<_T1_param>(__t1), _VSTD::forward<_T2_param>(__t2)) {}
#if defined(_LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS) && !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
_LIBCPP_INLINE_VISIBILITY
__compressed_pair(const __compressed_pair& __p)
_NOEXCEPT_(is_nothrow_copy_constructible<_T1>::value &&
is_nothrow_copy_constructible<_T2>::value)
: base(__p) {}
_LIBCPP_INLINE_VISIBILITY
__compressed_pair& operator=(const __compressed_pair& __p)
_NOEXCEPT_(is_nothrow_copy_assignable<_T1>::value &&
is_nothrow_copy_assignable<_T2>::value)
{
base::operator=(__p);
return *this;
}
_LIBCPP_INLINE_VISIBILITY
__compressed_pair(__compressed_pair&& __p)
_NOEXCEPT_(is_nothrow_move_constructible<_T1>::value &&
is_nothrow_move_constructible<_T2>::value)
: base(_VSTD::move(__p)) {}
_LIBCPP_INLINE_VISIBILITY
__compressed_pair& operator=(__compressed_pair&& __p)
_NOEXCEPT_(is_nothrow_move_assignable<_T1>::value &&
is_nothrow_move_assignable<_T2>::value)
{
base::operator=(_VSTD::move(__p));
return *this;
}
#endif // defined(_LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS) && !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
#ifndef _LIBCPP_HAS_NO_VARIADICS
template <class... _Args1, class... _Args2>
_LIBCPP_INLINE_VISIBILITY
__compressed_pair(piecewise_construct_t __pc, tuple<_Args1...> __first_args,
tuple<_Args2...> __second_args)
: base(__pc, _VSTD::move(__first_args), _VSTD::move(__second_args),
typename __make_tuple_indices<sizeof...(_Args1)>::type(),
typename __make_tuple_indices<sizeof...(_Args2) >::type())
{}
#endif // _LIBCPP_HAS_NO_VARIADICS
_LIBCPP_INLINE_VISIBILITY _T1_reference first() _NOEXCEPT {return base::first();}
_LIBCPP_INLINE_VISIBILITY _T1_const_reference first() const _NOEXCEPT {return base::first();}
_LIBCPP_INLINE_VISIBILITY _T2_reference second() _NOEXCEPT {return base::second();}
_LIBCPP_INLINE_VISIBILITY _T2_const_reference second() const _NOEXCEPT {return base::second();}
_LIBCPP_INLINE_VISIBILITY void swap(__compressed_pair& __x)
_NOEXCEPT_(__is_nothrow_swappable<_T1>::value &&
__is_nothrow_swappable<_T2>::value)
{base::swap(__x);}
};
_VSTD在/c++/v1/__config中定义为
#define _VSTD std::_LIBCPP_NAMESPACE
#define _VSTD std::_LIBCPP_NAMESPACE
#define _VSTD std
#define _VSTD std::_LIBCPP_NAMESPACE
__compressed_pair继承（private）了__libcpp_compressed_pair_imp
template <class _T1, class _T2, unsigned = __libcpp_compressed_pair_switch<_T1, _T2>::value> class __libcpp_compressed_pair_imp;
下面是__libcpp_compressed_pair_imp的几个模板特化
0
template <class _T1, class _T2>
class __libcpp_compressed_pair_imp<_T1, _T2, 0>
{
private:
_T1 __first_;
_T2 __second_;
public:
typedef _T1 _T1_param;
typedef _T2 _T2_param;
typedef typename remove_reference<_T1>::type& _T1_reference;
typedef typename remove_reference<_T2>::type& _T2_reference;
typedef const typename remove_reference<_T1>::type& _T1_const_reference;
typedef const typename remove_reference<_T2>::type& _T2_const_reference;
_LIBCPP_INLINE_VISIBILITY __libcpp_compressed_pair_imp() : __first_(), __second_() {}
_LIBCPP_INLINE_VISIBILITY explicit __libcpp_compressed_pair_imp(_T1_param __t1)
: __first_(_VSTD::forward<_T1_param>(__t1)), __second_() {}
_LIBCPP_INLINE_VISIBILITY explicit __libcpp_compressed_pair_imp(_T2_param __t2)
: __first_(), __second_(_VSTD::forward<_T2_param>(__t2)) {}
_LIBCPP_INLINE_VISIBILITY __libcpp_compressed_pair_imp(_T1_param __t1, _T2_param __t2)
: __first_(_VSTD::forward<_T1_param>(__t1)), __second_(_VSTD::forward<_T2_param>(__t2)) {}
#if defined(_LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS) && !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp(const __libcpp_compressed_pair_imp& __p)
_NOEXCEPT_(is_nothrow_copy_constructible<_T1>::value &&
is_nothrow_copy_constructible<_T2>::value)
: __first_(__p.first()),
__second_(__p.second()) {}
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp& operator=(const __libcpp_compressed_pair_imp& __p)
_NOEXCEPT_(is_nothrow_copy_assignable<_T1>::value &&
is_nothrow_copy_assignable<_T2>::value)
{
__first_ = __p.first();
__second_ = __p.second();
return *this;
}
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp(__libcpp_compressed_pair_imp&& __p)
_NOEXCEPT_(is_nothrow_move_constructible<_T1>::value &&
is_nothrow_move_constructible<_T2>::value)
: __first_(_VSTD::forward<_T1>(__p.first())),
__second_(_VSTD::forward<_T2>(__p.second())) {}
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp& operator=(__libcpp_compressed_pair_imp&& __p)
_NOEXCEPT_(is_nothrow_move_assignable<_T1>::value &&
is_nothrow_move_assignable<_T2>::value)
{
__first_ = _VSTD::forward<_T1>(__p.first());
__second_ = _VSTD::forward<_T2>(__p.second());
return *this;
}
#endif // defined(_LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS) && !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
#ifndef _LIBCPP_HAS_NO_VARIADICS
template <class... _Args1, class... _Args2, size_t... _I1, size_t... _I2>
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp(piecewise_construct_t __pc,
tuple<_Args1...> __first_args,
tuple<_Args2...> __second_args,
__tuple_indices<_I1...>,
__tuple_indices<_I2...>)
: __first_(_VSTD::forward<_Args1>(_VSTD::get<_I1>(__first_args))...),
__second_(_VSTD::forward<_Args2>(_VSTD::get<_I2>(__second_args))...)
{}
#endif // _LIBCPP_HAS_NO_VARIADICS
_LIBCPP_INLINE_VISIBILITY _T1_reference first() _NOEXCEPT {return __first_;}
_LIBCPP_INLINE_VISIBILITY _T1_const_reference first() const _NOEXCEPT {return __first_;}
_LIBCPP_INLINE_VISIBILITY _T2_reference second() _NOEXCEPT {return __second_;}
_LIBCPP_INLINE_VISIBILITY _T2_const_reference second() const _NOEXCEPT {return __second_;}
_LIBCPP_INLINE_VISIBILITY void swap(__libcpp_compressed_pair_imp& __x)
_NOEXCEPT_(__is_nothrow_swappable<_T1>::value &&
__is_nothrow_swappable<_T2>::value)
{
using _VSTD::swap;
swap(__first_, __x.__first_);
swap(__second_, __x.__second_);
}
};
1
template <class _T1, class _T2>
class __libcpp_compressed_pair_imp<_T1, _T2, 1>
: private _T1
{
private:
_T2 __second_;
public:
typedef _T1 _T1_param;
typedef _T2 _T2_param;
typedef _T1& _T1_reference;
typedef typename remove_reference<_T2>::type& _T2_reference;
typedef const _T1& _T1_const_reference;
typedef const typename remove_reference<_T2>::type& _T2_const_reference;
_LIBCPP_INLINE_VISIBILITY __libcpp_compressed_pair_imp() : __second_() {}
_LIBCPP_INLINE_VISIBILITY explicit __libcpp_compressed_pair_imp(_T1_param __t1)
: _T1(_VSTD::forward<_T1_param>(__t1)), __second_() {}
_LIBCPP_INLINE_VISIBILITY explicit __libcpp_compressed_pair_imp(_T2_param __t2)
: __second_(_VSTD::forward<_T2_param>(__t2)) {}
_LIBCPP_INLINE_VISIBILITY __libcpp_compressed_pair_imp(_T1_param __t1, _T2_param __t2)
: _T1(_VSTD::forward<_T1_param>(__t1)), __second_(_VSTD::forward<_T2_param>(__t2)) {}
#if defined(_LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS) && !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp(const __libcpp_compressed_pair_imp& __p)
_NOEXCEPT_(is_nothrow_copy_constructible<_T1>::value &&
is_nothrow_copy_constructible<_T2>::value)
: _T1(__p.first()), __second_(__p.second()) {}
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp& operator=(const __libcpp_compressed_pair_imp& __p)
_NOEXCEPT_(is_nothrow_copy_assignable<_T1>::value &&
is_nothrow_copy_assignable<_T2>::value)
{
_T1::operator=(__p.first());
__second_ = __p.second();
return *this;
}
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp(__libcpp_compressed_pair_imp&& __p)
_NOEXCEPT_(is_nothrow_move_constructible<_T1>::value &&
is_nothrow_move_constructible<_T2>::value)
: _T1(_VSTD::move(__p.first())), __second_(_VSTD::forward<_T2>(__p.second())) {}
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp& operator=(__libcpp_compressed_pair_imp&& __p)
_NOEXCEPT_(is_nothrow_move_assignable<_T1>::value &&
is_nothrow_move_assignable<_T2>::value)
{
_T1::operator=(_VSTD::move(__p.first()));
__second_ = _VSTD::forward<_T2>(__p.second());
return *this;
}
#endif // defined(_LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS) && !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
#ifndef _LIBCPP_HAS_NO_VARIADICS
template <class... _Args1, class... _Args2, size_t... _I1, size_t... _I2>
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp(piecewise_construct_t __pc,
tuple<_Args1...> __first_args,
tuple<_Args2...> __second_args,
__tuple_indices<_I1...>,
__tuple_indices<_I2...>)
: _T1(_VSTD::forward<_Args1>(_VSTD::get<_I1>(__first_args))...),
__second_(_VSTD::forward<_Args2>(_VSTD::get<_I2>(__second_args))...)
{}
#endif // _LIBCPP_HAS_NO_VARIADICS
_LIBCPP_INLINE_VISIBILITY _T1_reference first() _NOEXCEPT {return *this;}
_LIBCPP_INLINE_VISIBILITY _T1_const_reference first() const _NOEXCEPT {return *this;}
_LIBCPP_INLINE_VISIBILITY _T2_reference second() _NOEXCEPT {return __second_;}
_LIBCPP_INLINE_VISIBILITY _T2_const_reference second() const _NOEXCEPT {return __second_;}
_LIBCPP_INLINE_VISIBILITY void swap(__libcpp_compressed_pair_imp& __x)
_NOEXCEPT_(__is_nothrow_swappable<_T1>::value &&
__is_nothrow_swappable<_T2>::value)
{
using _VSTD::swap;
swap(__second_, __x.__second_);
}
};
2
template <class _T1, class _T2>
class __libcpp_compressed_pair_imp<_T1, _T2, 2>
: private _T2
{
private:
_T1 __first_;
public:
typedef _T1 _T1_param;
typedef _T2 _T2_param;
typedef typename remove_reference<_T1>::type& _T1_reference;
typedef _T2& _T2_reference;
typedef const typename remove_reference<_T1>::type& _T1_const_reference;
typedef const _T2& _T2_const_reference;
_LIBCPP_INLINE_VISIBILITY __libcpp_compressed_pair_imp() : __first_() {}
_LIBCPP_INLINE_VISIBILITY explicit __libcpp_compressed_pair_imp(_T1_param __t1)
: __first_(_VSTD::forward<_T1_param>(__t1)) {}
_LIBCPP_INLINE_VISIBILITY explicit __libcpp_compressed_pair_imp(_T2_param __t2)
: _T2(_VSTD::forward<_T2_param>(__t2)), __first_() {}
_LIBCPP_INLINE_VISIBILITY __libcpp_compressed_pair_imp(_T1_param __t1, _T2_param __t2)
_NOEXCEPT_(is_nothrow_move_constructible<_T1>::value &&
is_nothrow_move_constructible<_T2>::value)
: _T2(_VSTD::forward<_T2_param>(__t2)), __first_(_VSTD::forward<_T1_param>(__t1)) {}
#if defined(_LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS) && !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp(const __libcpp_compressed_pair_imp& __p)
_NOEXCEPT_(is_nothrow_copy_constructible<_T1>::value &&
is_nothrow_copy_constructible<_T2>::value)
: _T2(__p.second()), __first_(__p.first()) {}
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp& operator=(const __libcpp_compressed_pair_imp& __p)
_NOEXCEPT_(is_nothrow_copy_assignable<_T1>::value &&
is_nothrow_copy_assignable<_T2>::value)
{
_T2::operator=(__p.second());
__first_ = __p.first();
return *this;
}
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp(__libcpp_compressed_pair_imp&& __p)
_NOEXCEPT_(is_nothrow_move_constructible<_T1>::value &&
is_nothrow_move_constructible<_T2>::value)
: _T2(_VSTD::forward<_T2>(__p.second())), __first_(_VSTD::move(__p.first())) {}
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp& operator=(__libcpp_compressed_pair_imp&& __p)
_NOEXCEPT_(is_nothrow_move_assignable<_T1>::value &&
is_nothrow_move_assignable<_T2>::value)
{
_T2::operator=(_VSTD::forward<_T2>(__p.second()));
__first_ = _VSTD::move(__p.first());
return *this;
}
#endif // defined(_LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS) && !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
#ifndef _LIBCPP_HAS_NO_VARIADICS
template <class... _Args1, class... _Args2, size_t... _I1, size_t... _I2>
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp(piecewise_construct_t __pc,
tuple<_Args1...> __first_args,
tuple<_Args2...> __second_args,
__tuple_indices<_I1...>,
__tuple_indices<_I2...>)
: _T2(_VSTD::forward<_Args2>(_VSTD::get<_I2>(__second_args))...),
__first_(_VSTD::forward<_Args1>(_VSTD::get<_I1>(__first_args))...)
{}
#endif // _LIBCPP_HAS_NO_VARIADICS
_LIBCPP_INLINE_VISIBILITY _T1_reference first() _NOEXCEPT {return __first_;}
_LIBCPP_INLINE_VISIBILITY _T1_const_reference first() const _NOEXCEPT {return __first_;}
_LIBCPP_INLINE_VISIBILITY _T2_reference second() _NOEXCEPT {return *this;}
_LIBCPP_INLINE_VISIBILITY _T2_const_reference second() const _NOEXCEPT {return *this;}
_LIBCPP_INLINE_VISIBILITY void swap(__libcpp_compressed_pair_imp& __x)
_NOEXCEPT_(__is_nothrow_swappable<_T1>::value &&
__is_nothrow_swappable<_T2>::value)
{
using _VSTD::swap;
swap(__first_, __x.__first_);
}
};
3
template <class _T1, class _T2>
class __libcpp_compressed_pair_imp<_T1, _T2, 3>
: private _T1,
private _T2
{
public:
typedef _T1 _T1_param;
typedef _T2 _T2_param;
typedef _T1& _T1_reference;
typedef _T2& _T2_reference;
typedef const _T1& _T1_const_reference;
typedef const _T2& _T2_const_reference;
_LIBCPP_INLINE_VISIBILITY __libcpp_compressed_pair_imp() {}
_LIBCPP_INLINE_VISIBILITY explicit __libcpp_compressed_pair_imp(_T1_param __t1)
: _T1(_VSTD::forward<_T1_param>(__t1)) {}
_LIBCPP_INLINE_VISIBILITY explicit __libcpp_compressed_pair_imp(_T2_param __t2)
: _T2(_VSTD::forward<_T2_param>(__t2)) {}
_LIBCPP_INLINE_VISIBILITY __libcpp_compressed_pair_imp(_T1_param __t1, _T2_param __t2)
: _T1(_VSTD::forward<_T1_param>(__t1)), _T2(_VSTD::forward<_T2_param>(__t2)) {}
#if defined(_LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS) && !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp(const __libcpp_compressed_pair_imp& __p)
_NOEXCEPT_(is_nothrow_copy_constructible<_T1>::value &&
is_nothrow_copy_constructible<_T2>::value)
: _T1(__p.first()), _T2(__p.second()) {}
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp& operator=(const __libcpp_compressed_pair_imp& __p)
_NOEXCEPT_(is_nothrow_copy_assignable<_T1>::value &&
is_nothrow_copy_assignable<_T2>::value)
{
_T1::operator=(__p.first());
_T2::operator=(__p.second());
return *this;
}
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp(__libcpp_compressed_pair_imp&& __p)
_NOEXCEPT_(is_nothrow_move_constructible<_T1>::value &&
is_nothrow_move_constructible<_T2>::value)
: _T1(_VSTD::move(__p.first())), _T2(_VSTD::move(__p.second())) {}
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp& operator=(__libcpp_compressed_pair_imp&& __p)
_NOEXCEPT_(is_nothrow_move_assignable<_T1>::value &&
is_nothrow_move_assignable<_T2>::value)
{
_T1::operator=(_VSTD::move(__p.first()));
_T2::operator=(_VSTD::move(__p.second()));
return *this;
}
#endif // defined(_LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS) && !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
#ifndef _LIBCPP_HAS_NO_VARIADICS
template <class... _Args1, class... _Args2, size_t... _I1, size_t... _I2>
_LIBCPP_INLINE_VISIBILITY
__libcpp_compressed_pair_imp(piecewise_construct_t __pc,
tuple<_Args1...> __first_args,
tuple<_Args2...> __second_args,
__tuple_indices<_I1...>,
__tuple_indices<_I2...>)
: _T1(_VSTD::forward<_Args1>(_VSTD::get<_I1>(__first_args))...),
_T2(_VSTD::forward<_Args2>(_VSTD::get<_I2>(__second_args))...)
{}
#endif // _LIBCPP_HAS_NO_VARIADICS
_LIBCPP_INLINE_VISIBILITY _T1_reference first() _NOEXCEPT {return *this;}
_LIBCPP_INLINE_VISIBILITY _T1_const_reference first() const _NOEXCEPT {return *this;}
_LIBCPP_INLINE_VISIBILITY _T2_reference second() _NOEXCEPT {return *this;}
_LIBCPP_INLINE_VISIBILITY _T2_const_reference second() const _NOEXCEPT {return *this;}
_LIBCPP_INLINE_VISIBILITY void swap(__libcpp_compressed_pair_imp&)
_NOEXCEPT_(__is_nothrow_swappable<_T1>::value &&
__is_nothrow_swappable<_T2>::value)
{
}
};
构造
constexpr unique_ptr() noexcept;
_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR unique_ptr() _NOEXCEPT
: __ptr_(pointer())
{
static_assert(!is_pointer<deleter_type>::value,
"unique_ptr constructed with null function pointer deleter");
}
explicit unique_ptr(pointer p) noexcept;
_LIBCPP_INLINE_VISIBILITY explicit unique_ptr(pointer __p) _NOEXCEPT
: __ptr_(_VSTD::move(__p))
{
static_assert(!is_pointer<deleter_type>::value,
"unique_ptr constructed with null function pointer deleter");
}
unique_ptr(pointer p, see below d1) noexcept;
unique_ptr(pointer p, see below d2) noexcept;
unique_ptr(unique_ptr&& u) noexcept;
unique_ptr(nullptr_t) noexcept : unique_ptr() { }
还有两个构造函数是函数模板，构造函数是模板的不多见。
template <class U, class E> unique_ptr(unique_ptr<U, E>&& u) noexcept;
template <class U> unique_ptr(auto_ptr<U>&& u) noexcept;
template <class _Tp, class _Dp = default_delete<_Tp> >
class _LIBCPP_TYPE_VIS_ONLY unique_ptr
{
public:
typedef _Tp element_type;
typedef _Dp deleter_type;
typedef typename __pointer_type<_Tp, deleter_type>::type pointer;
private:
__compressed_pair<pointer, deleter_type> __ptr_;
#ifdef _LIBCPP_HAS_NO_RVALUE_REFERENCES
unique_ptr(unique_ptr&);
template <class _Up, class _Ep>
unique_ptr(unique_ptr<_Up, _Ep>&);
unique_ptr& operator=(unique_ptr&);
template <class _Up, class _Ep>
unique_ptr& operator=(unique_ptr<_Up, _Ep>&);
#endif // _LIBCPP_HAS_NO_RVALUE_REFERENCES
struct __nat {int __for_bool_;};
typedef typename remove_reference<deleter_type>::type& _Dp_reference;
typedef const typename remove_reference<deleter_type>::type& _Dp_const_reference;
public:
_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR unique_ptr() _NOEXCEPT
: __ptr_(pointer())
{
static_assert(!is_pointer<deleter_type>::value,
"unique_ptr constructed with null function pointer deleter");
}
_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR unique_ptr(nullptr_t) _NOEXCEPT
: __ptr_(pointer())
{
static_assert(!is_pointer<deleter_type>::value,
"unique_ptr constructed with null function pointer deleter");
}
_LIBCPP_INLINE_VISIBILITY explicit unique_ptr(pointer __p) _NOEXCEPT
: __ptr_(_VSTD::move(__p))
{
static_assert(!is_pointer<deleter_type>::value,
"unique_ptr constructed with null function pointer deleter");
}
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
_LIBCPP_INLINE_VISIBILITY unique_ptr(pointer __p, typename conditional<
is_reference<deleter_type>::value,
deleter_type,
typename add_lvalue_reference<const deleter_type>::type>::type __d)
_NOEXCEPT
: __ptr_(__p, __d) {}
_LIBCPP_INLINE_VISIBILITY unique_ptr(pointer __p, typename remove_reference<deleter_type>::type&& __d)
_NOEXCEPT
: __ptr_(__p, _VSTD::move(__d))
{
static_assert(!is_reference<deleter_type>::value, "rvalue deleter bound to reference");
}
_LIBCPP_INLINE_VISIBILITY unique_ptr(unique_ptr&& __u) _NOEXCEPT
: __ptr_(__u.release(), _VSTD::forward<deleter_type>(__u.get_deleter())) {}
template <class _Up, class _Ep>
_LIBCPP_INLINE_VISIBILITY
unique_ptr(unique_ptr<_Up, _Ep>&& __u,
typename enable_if
<
!is_array<_Up>::value &&
is_convertible<typename unique_ptr<_Up, _Ep>::pointer, pointer>::value &&
is_convertible<_Ep, deleter_type>::value &&
(
!is_reference<deleter_type>::value ||
is_same<deleter_type, _Ep>::value
),
__nat
>::type = __nat()) _NOEXCEPT
: __ptr_(__u.release(), _VSTD::forward<_Ep>(__u.get_deleter())) {}
template <class _Up>
_LIBCPP_INLINE_VISIBILITY unique_ptr(auto_ptr<_Up>&& __p,
typename enable_if<
is_convertible<_Up*, _Tp*>::value &&
is_same<_Dp, default_delete<_Tp> >::value,
__nat
>::type = __nat()) _NOEXCEPT
: __ptr_(__p.release())
{
}
_LIBCPP_INLINE_VISIBILITY unique_ptr& operator=(unique_ptr&& __u) _NOEXCEPT
{
reset(__u.release());
__ptr_.second() = _VSTD::forward<deleter_type>(__u.get_deleter());
return *this;
}
template <class _Up, class _Ep>
_LIBCPP_INLINE_VISIBILITY
typename enable_if
<
!is_array<_Up>::value &&
is_convertible<typename unique_ptr<_Up, _Ep>::pointer, pointer>::value &&
is_assignable<deleter_type&, _Ep&&>::value,
unique_ptr&
>::type
operator=(unique_ptr<_Up, _Ep>&& __u) _NOEXCEPT
{
reset(__u.release());
__ptr_.second() = _VSTD::forward<_Ep>(__u.get_deleter());
return *this;
}
#else // _LIBCPP_HAS_NO_RVALUE_REFERENCES
_LIBCPP_INLINE_VISIBILITY operator __rv<unique_ptr>()
{
return __rv<unique_ptr>(*this);
}
_LIBCPP_INLINE_VISIBILITY unique_ptr(__rv<unique_ptr> __u)
: __ptr_(__u->release(), _VSTD::forward<deleter_type>(__u->get_deleter())) {}
template <class _Up, class _Ep>
_LIBCPP_INLINE_VISIBILITY unique_ptr& operator=(unique_ptr<_Up, _Ep> __u)
{
reset(__u.release());
__ptr_.second() = _VSTD::forward<deleter_type>(__u.get_deleter());
return *this;
}
_LIBCPP_INLINE_VISIBILITY unique_ptr(pointer __p, deleter_type __d)
: __ptr_(_VSTD::move(__p), _VSTD::move(__d)) {}
template <class _Up>
_LIBCPP_INLINE_VISIBILITY
typename enable_if<
is_convertible<_Up*, _Tp*>::value &&
is_same<_Dp, default_delete<_Tp> >::value,
unique_ptr&
>::type
operator=(auto_ptr<_Up> __p)
{reset(__p.release()); return *this;}
#endif // _LIBCPP_HAS_NO_RVALUE_REFERENCES
_LIBCPP_INLINE_VISIBILITY ~unique_ptr() {reset();}
_LIBCPP_INLINE_VISIBILITY unique_ptr& operator=(nullptr_t) _NOEXCEPT
{
reset();
return *this;
}
_LIBCPP_INLINE_VISIBILITY typename add_lvalue_reference<_Tp>::type operator*() const
{return *__ptr_.first();}
_LIBCPP_INLINE_VISIBILITY pointer operator->() const _NOEXCEPT {return __ptr_.first();}
_LIBCPP_INLINE_VISIBILITY pointer get() const _NOEXCEPT {return __ptr_.first();}
_LIBCPP_INLINE_VISIBILITY _Dp_reference get_deleter() _NOEXCEPT
{return __ptr_.second();}
_LIBCPP_INLINE_VISIBILITY _Dp_const_reference get_deleter() const _NOEXCEPT
{return __ptr_.second();}
_LIBCPP_INLINE_VISIBILITY
_LIBCPP_EXPLICIT operator bool() const _NOEXCEPT
{return __ptr_.first() != nullptr;}
_LIBCPP_INLINE_VISIBILITY pointer release() _NOEXCEPT
{
pointer __t = __ptr_.first();
__ptr_.first() = pointer();
return __t;
}
_LIBCPP_INLINE_VISIBILITY void reset(pointer __p = pointer()) _NOEXCEPT
{
pointer __tmp = __ptr_.first();
__ptr_.first() = __p;
if (__tmp)
__ptr_.second()(__tmp);
}
_LIBCPP_INLINE_VISIBILITY void swap(unique_ptr& __u) _NOEXCEPT
{__ptr_.swap(__u.__ptr_);}
};
参考libstdc++-v3/include/bits/unique_ptr.h
template <typename _Tp, typename _Dp = default_delete<_Tp>>
class unique_ptr
{
template <typename _Up>
using _DeleterConstraint =
typename __uniq_ptr_impl<_Tp, _Up>::_DeleterConstraint::type;
__uniq_ptr_data<_Tp, _Dp> _M_t;
public:
using pointer = typename __uniq_ptr_impl<_Tp, _Dp>::pointer;
using element_type = _Tp;
using deleter_type = _Dp;
private:
// helper template for detecting a safe conversion from another
// unique_ptr
template<typename _Up, typename _Ep>
using __safe_conversion_up = __and_<
is_convertible<typename unique_ptr<_Up, _Ep>::pointer, pointer>,
__not_<is_array<_Up>>
>;
public:
// Constructors.
/// Default constructor, creates a unique_ptr that owns nothing.
template<typename _Del = _Dp, typename = _DeleterConstraint<_Del>>
constexpr unique_ptr() noexcept
: _M_t()
{ }
/** Takes ownership of a pointer.
*
* @param __p A pointer to an object of @c element_type
*
* The deleter will be value-initialized.
*/
template<typename _Del = _Dp, typename = _DeleterConstraint<_Del>>
_GLIBCXX23_CONSTEXPR
explicit
unique_ptr(pointer __p) noexcept
: _M_t(__p)
{ }
/** Takes ownership of a pointer.
*
* @param __p A pointer to an object of @c element_type
* @param __d A reference to a deleter.
*
* The deleter will be initialized with @p __d
*/
template<typename _Del = deleter_type,
typename = _Require<is_copy_constructible<_Del>>>
_GLIBCXX23_CONSTEXPR
unique_ptr(pointer __p, const deleter_type& __d) noexcept
: _M_t(__p, __d) { }
/** Takes ownership of a pointer.
*
* @param __p A pointer to an object of @c element_type
* @param __d An rvalue reference to a (non-reference) deleter.
*
* The deleter will be initialized with @p std::move(__d)
*/
template<typename _Del = deleter_type,
typename = _Require<is_move_constructible<_Del>>>
_GLIBCXX23_CONSTEXPR
unique_ptr(pointer __p,
__enable_if_t<!is_lvalue_reference<_Del>::value,
_Del&&> __d) noexcept
: _M_t(__p, std::move(__d))
{ }
template<typename _Del = deleter_type,
typename _DelUnref = typename remove_reference<_Del>::type>
_GLIBCXX23_CONSTEXPR
unique_ptr(pointer,
__enable_if_t<is_lvalue_reference<_Del>::value,
_DelUnref&&>) = delete;
/// Creates a unique_ptr that owns nothing.
template<typename _Del = _Dp, typename = _DeleterConstraint<_Del>>
constexpr unique_ptr(nullptr_t) noexcept
: _M_t()
{ }
// Move constructors.
/// Move constructor.
unique_ptr(unique_ptr&&) = default;
/** @brief Converting constructor from another type
*
* Requires that the pointer owned by @p __u is convertible to the
* type of pointer owned by this object, @p __u does not own an array,
* and @p __u has a compatible deleter type.
*/
template<typename _Up, typename _Ep, typename = _Require<
__safe_conversion_up<_Up, _Ep>,
__conditional_t<is_reference<_Dp>::value,
is_same<_Ep, _Dp>,
is_convertible<_Ep, _Dp>>>>
_GLIBCXX23_CONSTEXPR
unique_ptr(unique_ptr<_Up, _Ep>&& __u) noexcept
: _M_t(__u.release(), std::forward<_Ep>(__u.get_deleter()))
{ }
#if _GLIBCXX_USE_DEPRECATED
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
/// Converting constructor from @c auto_ptr
template<typename _Up, typename = _Require<
is_convertible<_Up*, _Tp*>, is_same<_Dp, default_delete<_Tp>>>>
unique_ptr(auto_ptr<_Up>&& __u) noexcept;
#pragma GCC diagnostic pop
#endif
/// Destructor, invokes the deleter if the stored pointer is not null.
#if __cplusplus > 202002L && __cpp_constexpr_dynamic_alloc
constexpr
#endif
~unique_ptr() noexcept
{
static_assert(__is_invocable<deleter_type&, pointer>::value,
"unique_ptr's deleter must be invocable with a pointer");
auto& __ptr = _M_t._M_ptr();
if (__ptr != nullptr)
get_deleter()(std::move(__ptr));
__ptr = pointer();
}
// Assignment.
/** @brief Move assignment operator.
*
* Invokes the deleter if this object owns a pointer.
*/
unique_ptr& operator=(unique_ptr&&) = default;
/** @brief Assignment from another type.
*
* @param __u The object to transfer ownership from, which owns a
* convertible pointer to a non-array object.
*
* Invokes the deleter if this object owns a pointer.
*/
template<typename _Up, typename _Ep>
_GLIBCXX23_CONSTEXPR
typename enable_if< __and_<
__safe_conversion_up<_Up, _Ep>,
is_assignable<deleter_type&, _Ep&&>
>::value,
unique_ptr&>::type
operator=(unique_ptr<_Up, _Ep>&& __u) noexcept
{
reset(__u.release());
get_deleter() = std::forward<_Ep>(__u.get_deleter());
return *this;
}
/// Reset the %unique_ptr to empty, invoking the deleter if necessary.
_GLIBCXX23_CONSTEXPR
unique_ptr&
operator=(nullptr_t) noexcept
{
reset();
return *this;
}
// Observers.
/// Dereference the stored pointer.
_GLIBCXX23_CONSTEXPR
typename add_lvalue_reference<element_type>::type
operator*() const noexcept(noexcept(*std::declval<pointer>()))
{
__glibcxx_assert(get() != pointer());
return *get();
}
/// Return the stored pointer.
_GLIBCXX23_CONSTEXPR
pointer
operator->() const noexcept
{
_GLIBCXX_DEBUG_PEDASSERT(get() != pointer());
return get();
}
/// Return the stored pointer.
_GLIBCXX23_CONSTEXPR
pointer
get() const noexcept
{ return _M_t._M_ptr(); }
/// Return a reference to the stored deleter.
_GLIBCXX23_CONSTEXPR
deleter_type&
get_deleter() noexcept
{ return _M_t._M_deleter(); }
/// Return a reference to the stored deleter.
_GLIBCXX23_CONSTEXPR
const deleter_type&
get_deleter() const noexcept
{ return _M_t._M_deleter(); }
/// Return @c true if the stored pointer is not null.
_GLIBCXX23_CONSTEXPR
explicit operator bool() const noexcept
{ return get() == pointer() ? false : true; }
// Modifiers.
/// Release ownership of any stored pointer.
_GLIBCXX23_CONSTEXPR
pointer
release() noexcept
{ return _M_t.release(); }
/** @brief Replace the stored pointer.
*
* @param __p The new pointer to store.
*
* The deleter will be invoked if a pointer is already owned.
*/
_GLIBCXX23_CONSTEXPR
void
reset(pointer __p = pointer()) noexcept
{
static_assert(__is_invocable<deleter_type&, pointer>::value,
"unique_ptr's deleter must be invocable with a pointer");
_M_t.reset(std::move(__p));
}
/// Exchange the pointer and deleter with another object.
_GLIBCXX23_CONSTEXPR
void
swap(unique_ptr& __u) noexcept
{
static_assert(__is_swappable<_Dp>::value, "deleter must be swappable");
_M_t.swap(__u._M_t);
}
// Disable copy from lvalue.
unique_ptr(const unique_ptr&) = delete;
unique_ptr& operator=(const unique_ptr&) = delete;
};
示例
#include <iostream>
#include <memory>
int main()
{
int *i = new int(100);
std::unique_ptr<int> p(i);
std::cout<<"i="<<*p<<std::endl;
return 0;
}
shared_ptr
template<class T>
class shared_ptr
{
public:
typedef T element_type;
// constructors:
constexpr shared_ptr() noexcept;
template<class Y> explicit shared_ptr(Y* p);
template<class Y, class D> shared_ptr(Y* p, D d);
template<class Y, class D, class A> shared_ptr(Y* p, D d, A a);
template <class D> shared_ptr(nullptr_t p, D d);
template <class D, class A> shared_ptr(nullptr_t p, D d, A a);
template<class Y> shared_ptr(const shared_ptr<Y>& r, T *p) noexcept;
shared_ptr(const shared_ptr& r) noexcept;
template<class Y> shared_ptr(const shared_ptr<Y>& r) noexcept;
shared_ptr(shared_ptr&& r) noexcept;
template<class Y> shared_ptr(shared_ptr<Y>&& r) noexcept;
template<class Y> explicit shared_ptr(const weak_ptr<Y>& r);
template<class Y> shared_ptr(auto_ptr<Y>&& r);
template <class Y, class D> shared_ptr(unique_ptr<Y, D>&& r);
shared_ptr(nullptr_t) : shared_ptr() { }
// destructor:
~shared_ptr();
// assignment:
shared_ptr& operator=(const shared_ptr& r) noexcept;
template<class Y> shared_ptr& operator=(const shared_ptr<Y>& r) noexcept;
shared_ptr& operator=(shared_ptr&& r) noexcept;
template<class Y> shared_ptr& operator=(shared_ptr<Y>&& r);
template<class Y> shared_ptr& operator=(auto_ptr<Y>&& r);
template <class Y, class D> shared_ptr& operator=(unique_ptr<Y, D>&& r);
// modifiers:
void swap(shared_ptr& r) noexcept;
void reset() noexcept;
template<class Y> void reset(Y* p);
template<class Y, class D> void reset(Y* p, D d);
template<class Y, class D, class A> void reset(Y* p, D d, A a);
// observers:
T* get() const noexcept;
T& operator*() const noexcept;
T* operator->() const noexcept;
long use_count() const noexcept;
bool unique() const noexcept;
explicit operator bool() const noexcept;
template<class U> bool owner_before(shared_ptr<U> const& b) const;
template<class U> bool owner_before(weak_ptr<U> const& b) const;
};
weak_ptr
template<class T>
class weak_ptr
{
public:
typedef T element_type;
// constructors
constexpr weak_ptr() noexcept;
template<class Y> weak_ptr(shared_ptr<Y> const& r) noexcept;
weak_ptr(weak_ptr const& r) noexcept;
template<class Y> weak_ptr(weak_ptr<Y> const& r) noexcept;
weak_ptr(weak_ptr&& r) noexcept; // C++14
template<class Y> weak_ptr(weak_ptr<Y>&& r) noexcept; // C++14
// destructor
~weak_ptr();
// assignment
weak_ptr& operator=(weak_ptr const& r) noexcept;
template<class Y> weak_ptr& operator=(weak_ptr<Y> const& r) noexcept;
template<class Y> weak_ptr& operator=(shared_ptr<Y> const& r) noexcept;
weak_ptr& operator=(weak_ptr&& r) noexcept; // C++14
template<class Y> weak_ptr& operator=(weak_ptr<Y>&& r) noexcept; // C++14
// modifiers
void swap(weak_ptr& r) noexcept;
void reset() noexcept;
// observers
long use_count() const noexcept;
bool expired() const noexcept;
shared_ptr<T> lock() const noexcept;
template<class U> bool owner_before(shared_ptr<U> const& b) const;
template<class U> bool owner_before(weak_ptr<U> const& b) const;
};
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