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regarded and expertly designed C++ library projects in the
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Coding Standards
Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
intrusive_ptr class template
Introduction
Synopsis
Members
Free Functions
The intrusive_ptr class template stores a pointer to an object with an embedded reference count. Every new intrusive_ptr instance increments the reference count by using an unqualified call to the function intrusive_ptr_add_ref, passing it the pointer as an argument. Similarly, when an intrusive_ptr is destroyed, it calls intrusive_ptr_release; this function is responsible for destroying the object when its reference count drops to zero. The user is expected to provide suitable definitions of these two functions. On compilers that support argument-dependent lookup, intrusive_ptr_add_ref and intrusive_ptr_release should be defined in the namespace that corresponds to their parameter; otherwise, the definitions need to go in namespace boost.
The class template is parameterized on T, the type of the object pointed to. intrusive_ptr<T> can be implicitly converted to intrusive_ptr<U> whenever T* can be implicitly converted to U*.
The main reasons to use intrusive_ptr are:
As a general rule, if it isn't obvious whether intrusive_ptr better fits your needs than shared_ptr, try a shared_ptr-based design first.
namespace boost {
template<class T> class intrusive_ptr {
public:
typedef T element_type;
intrusive_ptr(); // never throws
intrusive_ptr(T * p, bool add_ref = true);
intrusive_ptr(intrusive_ptr const & r);
template<class Y> intrusive_ptr(intrusive_ptr<Y> const & r);
~intrusive_ptr();
intrusive_ptr & operator=(intrusive_ptr const & r);
template<class Y> intrusive_ptr & operator=(intrusive_ptr<Y> const & r);
intrusive_ptr & operator=(T * r);
void reset();
void reset(T * r);
T & operator*() const; // never throws
T * operator->() const; // never throws
T * get() const; // never throws
operator unspecified-bool-type() const; // never throws
void swap(intrusive_ptr & b); // never throws
};
template<class T, class U>
bool operator==(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b); // never throws
template<class T, class U>
bool operator!=(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b); // never throws
template<class T>
bool operator==(intrusive_ptr<T> const & a, T * b); // never throws
template<class T>
bool operator!=(intrusive_ptr<T> const & a, T * b); // never throws
template<class T>
bool operator==(T * a, intrusive_ptr<T> const & b); // never throws
template<class T>
bool operator!=(T * a, intrusive_ptr<T> const & b); // never throws
template<class T, class U>
bool operator<(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b); // never throws
template<class T> void swap(intrusive_ptr<T> & a, intrusive_ptr<T> & b); // never throws
template<class T> T * get_pointer(intrusive_ptr<T> const & p); // never throws
template<class T, class U>
intrusive_ptr<T> static_pointer_cast(intrusive_ptr<U> const & r); // never throws
template<class T, class U>
intrusive_ptr<T> const_pointer_cast(intrusive_ptr<U> const & r); // never throws
template<class T, class U>
intrusive_ptr<T> dynamic_pointer_cast(intrusive_ptr<U> const & r); // never throws
template<class E, class T, class Y>
std::basic_ostream<E, T> & operator<< (std::basic_ostream<E, T> & os, intrusive_ptr<Y> const & p);
}
typedef T element_type;
Provides the type of the template parameter T.
intrusive_ptr(); // never throws
Postconditions:
get() == 0.Throws: nothing.
intrusive_ptr(T * p, bool add_ref = true);
Effects:
if(p != 0 && add_ref) intrusive_ptr_add_ref(p);.Postconditions:
get() == p.
intrusive_ptr(intrusive_ptr const & r); template<class Y> intrusive_ptr(intrusive_ptr<Y> const & r);
Effects:
if(r.get() != 0) intrusive_ptr_add_ref(r.get());.Postconditions:
get() == r.get().
~intrusive_ptr();
Effects:
if(get() != 0) intrusive_ptr_release(get());.
intrusive_ptr & operator=(intrusive_ptr const & r); template<class Y> intrusive_ptr & operator=(intrusive_ptr<Y> const & r); intrusive_ptr & operator=(T * r);
Effects: Equivalent to
intrusive_ptr(r).swap(*this).Returns:
*this.
void reset();
Effects: Equivalent to
intrusive_ptr().swap(*this).
void reset(T * r);
Effects: Equivalent to
intrusive_ptr(r).swap(*this).
T & operator*() const; // never throws
Requirements:
get() != 0.Returns:
*get().Throws: nothing.
T * operator->() const; // never throws
Requirements:
get() != 0.Returns:
get().Throws: nothing.
T * get() const; // never throws
Returns: the stored pointer.
Throws: nothing.
operator unspecified-bool-type () const; // never throws
Returns: an unspecified value that, when used in boolean contexts, is equivalent to
get() != 0.Throws: nothing.
Notes: This conversion operator allows intrusive_ptr objects to be used in boolean contexts, like
if (p && p->valid()) {}. The actual target type is typically a pointer to a member function, avoiding many of the implicit conversion pitfalls.
void swap(intrusive_ptr & b); // never throws
Effects: Exchanges the contents of the two smart pointers.
Throws: nothing.
template<class T, class U> bool operator==(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b); // never throws
Returns:
a.get() == b.get().Throws: nothing.
template<class T, class U> bool operator!=(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b); // never throws
Returns:
a.get() != b.get().Throws: nothing.
template<class T, class U> bool operator==(intrusive_ptr<T> const & a, U * b); // never throws
Returns:
a.get() == b.Throws: nothing.
template<class T, class U> bool operator!=(intrusive_ptr<T> const & a, U * b); // never throws
Returns:
a.get() != b.Throws: nothing.
template<class T, class U> bool operator==(T * a, intrusive_ptr<U> const & b); // never throws
Returns:
a == b.get().Throws: nothing.
template<class T, class U> bool operator!=(T * a, intrusive_ptr<U> const & b); // never throws
Returns:
a != b.get().Throws: nothing.
template<class T, class U> bool operator<(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b); // never throws
Returns:
std::less<T *>()(a.get(), b.get()).Throws: nothing.
Notes: Allows intrusive_ptr objects to be used as keys in associative containers.
template<class T> void swap(intrusive_ptr<T> & a, intrusive_ptr<T> & b); // never throws
Effects: Equivalent to
a.swap(b).Throws: nothing.
Notes: Matches the interface of std::swap. Provided as an aid to generic programming.
template<class T> T * get_pointer(intrusive_ptr<T> const & p); // never throws
Returns:
p.get().Throws: nothing.
Notes: Provided as an aid to generic programming. Used by mem_fn.
template<class T, class U> intrusive_ptr<T> static_pointer_cast(intrusive_ptr<U> const & r); // never throws
Returns:
intrusive_ptr<T>(static_cast<T*>(r.get())).Throws: nothing.
template<class T, class U> intrusive_ptr<T> const_pointer_cast(intrusive_ptr<U> const & r); // never throws
Returns:
intrusive_ptr<T>(const_cast<T*>(r.get())).Throws: nothing.
template<class T, class U> intrusive_ptr<T> dynamic_pointer_cast(intrusive_ptr<U> const & r);
Returns:
intrusive_ptr<T>(dynamic_cast<T*>(r.get())).Throws: nothing.
template<class E, class T, class Y>
std::basic_ostream<E, T> & operator<< (std::basic_ostream<E, T> & os, intrusive_ptr<Y> const & p);
Effects:
os << p.get();.Returns:
os.
$Date: 2008-07-12 07:37:16 -0400 (Sat, 12 Jul 2008) $
Copyright © 2003-2005 Peter Dimov. Distributed under the Boost Software License, Version 1.0. See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt.