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 library provides a helper base class template
intrusive_ref_counter which may
help adding support for intrusive_ptr to user types.
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:
intrusive_ptr
is the same as the corresponding raw pointer;intrusive_ptr<T> can be constructed from an arbitrary
raw pointer of type T *.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);
void reset(T * r, bool add_ref);
T & operator*() const; // never throws
T * operator->() const; // never throws
T * get() const; // never throws
T * detach(); // 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).
void reset(T * r, bool add_ref);
Effects: Equivalent to
intrusive_ptr(r, add_ref).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.
T * detach(); // never throws
Returns: the stored pointer.
Throws: nothing.
Postconditions:
get() == 0.Notes: The returned pointer has an elevated reference count. This allows conversion of an
intrusive_ptrback to a raw pointer, without the performance overhead of acquiring and dropping an extra reference. It can be viewed as the complement of the non-reference-incrementing constructor.Caution: Using
detachescapes the safety of automatic reference counting provided byintrusive_ptr. It should by used only where strictly necessary (such as when interfacing to an existing API), and when the implications are thoroughly understood.
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_ptrobjects to be used in boolean contexts, likeif (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_ptrobjects 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.
$Date$
Copyright © 2003-2005, 2013 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.