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321 lines
17 KiB
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<title>intrusive_ptr</title>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<body text="#000000" bgcolor="#ffffff" link="#0000ff" vlink="#0000ff">
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<h1><img height="86" alt="boost.png (6897 bytes)" src="../../boost.png"
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width="277" align="middle" border="0">intrusive_ptr class template</h1>
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<p>
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<a href="#Introduction">Introduction</a><br>
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<a href="#Synopsis">Synopsis</a><br>
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<a href="#Members">Members</a><br>
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<a href="#functions">Free Functions</a><br>
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</p>
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<h2><a name="Introduction">Introduction</a></h2>
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<p>The <code>intrusive_ptr</code> class template stores a pointer to an object with an
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embedded reference count. Every new <code>intrusive_ptr</code> instance increments
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the reference count by using an unqualified call to the function <code>intrusive_ptr_add_ref</code>,
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passing it the pointer as an argument. Similarly, when an <code>intrusive_ptr</code>
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is destroyed, it calls <code>intrusive_ptr_release</code>; this function is
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responsible for destroying the object when its reference count drops to zero.
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The user is expected to provide suitable definitions of these two functions. On
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compilers that support argument-dependent lookup, <code>intrusive_ptr_add_ref</code>
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and <code>intrusive_ptr_release</code> should be defined in the namespace
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that corresponds to their parameter; otherwise, the definitions need to go in
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namespace <code>boost</code>. The library provides a helper base class template
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<code><a href="intrusive_ref_counter.html">intrusive_ref_counter</a></code> which may
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help adding support for <code>intrusive_ptr</code> to user types.</p>
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<p>The class template is parameterized on <code>T</code>, the type of the object pointed
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to. <code>intrusive_ptr<T></code> can be implicitly converted to <code>intrusive_ptr<U></code>
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whenever <code>T*</code> can be implicitly converted to <code>U*</code>.</p>
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<p>The main reasons to use <code>intrusive_ptr</code> are:</p>
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<ul>
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<li>
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Some existing frameworks or OSes provide objects with embedded reference
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counts;</li>
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<li>
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The memory footprint of <code>intrusive_ptr</code>
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is the same as the corresponding raw pointer;</li>
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<li>
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<code>intrusive_ptr<T></code> can be constructed from an arbitrary
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raw pointer of type <code>T *</code>.</li></ul>
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<p>As a general rule, if it isn't obvious whether <code>intrusive_ptr</code> better
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fits your needs than <code>shared_ptr</code>, try a <code>shared_ptr</code>-based
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design first.</p>
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<h2><a name="Synopsis">Synopsis</a></h2>
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<pre>namespace boost {
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template<class T> class intrusive_ptr {
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public:
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typedef T <a href="#element_type" >element_type</a>;
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<a href="#constructors" >intrusive_ptr</a>(); // never throws
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<a href="#constructors" >intrusive_ptr</a>(T * p, bool add_ref = true);
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<a href="#constructors" >intrusive_ptr</a>(intrusive_ptr const & r);
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template<class Y> <a href="#constructors" >intrusive_ptr</a>(intrusive_ptr<Y> const & r);
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<a href="#destructor" >~intrusive_ptr</a>();
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intrusive_ptr & <a href="#assignment" >operator=</a>(intrusive_ptr const & r);
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template<class Y> intrusive_ptr & <a href="#assignment" >operator=</a>(intrusive_ptr<Y> const & r);
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intrusive_ptr & <a href="#assignment" >operator=</a>(T * r);
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void <a href="#reset" >reset</a>();
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void <a href="#reset" >reset</a>(T * r);
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void <a href="#reset" >reset</a>(T * r, bool add_ref);
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T & <a href="#indirection" >operator*</a>() const; // never throws
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T * <a href="#indirection" >operator-></a>() const; // never throws
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T * <a href="#get" >get</a>() const; // never throws
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T * <a href="#detach" >detach</a>(); // never throws
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operator <a href="#conversions" ><i>unspecified-bool-type</i></a>() const; // never throws
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void <a href="#swap" >swap</a>(intrusive_ptr & b); // never throws
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};
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template<class T, class U>
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bool <a href="#comparison" >operator==</a>(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b); // never throws
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template<class T, class U>
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bool <a href="#comparison" >operator!=</a>(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b); // never throws
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template<class T>
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bool <a href="#comparison" >operator==</a>(intrusive_ptr<T> const & a, T * b); // never throws
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template<class T>
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bool <a href="#comparison" >operator!=</a>(intrusive_ptr<T> const & a, T * b); // never throws
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template<class T>
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bool <a href="#comparison" >operator==</a>(T * a, intrusive_ptr<T> const & b); // never throws
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template<class T>
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bool <a href="#comparison" >operator!=</a>(T * a, intrusive_ptr<T> const & b); // never throws
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template<class T, class U>
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bool <a href="#comparison" >operator<</a>(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b); // never throws
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template<class T> void <a href="#free-swap" >swap</a>(intrusive_ptr<T> & a, intrusive_ptr<T> & b); // never throws
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template<class T> T * <a href="#get_pointer" >get_pointer</a>(intrusive_ptr<T> const & p); // never throws
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template<class T, class U>
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intrusive_ptr<T> <a href="#static_pointer_cast" >static_pointer_cast</a>(intrusive_ptr<U> const & r); // never throws
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template<class T, class U>
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intrusive_ptr<T> <a href="#const_pointer_cast" >const_pointer_cast</a>(intrusive_ptr<U> const & r); // never throws
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template<class T, class U>
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intrusive_ptr<T> <a href="#dynamic_pointer_cast" >dynamic_pointer_cast</a>(intrusive_ptr<U> const & r); // never throws
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template<class E, class T, class Y>
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std::basic_ostream<E, T> & <a href="#insertion-operator" >operator<<</a> (std::basic_ostream<E, T> & os, intrusive_ptr<Y> const & p);
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}</pre>
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<h2><a name="Members">Members</a></h2>
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<h3><a name="element_type">element_type</a></h3>
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<pre>typedef T element_type;</pre>
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<blockquote>
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<p>Provides the type of the template parameter <code>T</code>.</p>
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</blockquote>
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<h3><a name="constructors">constructors</a></h3>
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<pre>intrusive_ptr(); // never throws</pre>
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<blockquote>
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<p><b>Postconditions:</b> <code>get() == 0</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<pre>intrusive_ptr(T * p, bool add_ref = true);</pre>
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<blockquote>
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<p><b>Effects:</b> <code>if(p != 0 && add_ref) intrusive_ptr_add_ref(p);</code>.</p>
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<p><b>Postconditions:</b> <code>get() == p</code>.</p>
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</blockquote>
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<pre>intrusive_ptr(intrusive_ptr const & r);
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template<class Y> intrusive_ptr(intrusive_ptr<Y> const & r);</pre>
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<blockquote>
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<p><b>Effects:</b> <code>if(r.get() != 0) intrusive_ptr_add_ref(r.get());</code>.</p>
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<p><b>Postconditions:</b> <code>get() == r.get()</code>.</p>
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</blockquote>
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<h3><a name="destructor">destructor</a></h3>
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<pre>~intrusive_ptr();</pre>
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<blockquote>
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<p><b>Effects:</b> <code>if(get() != 0) intrusive_ptr_release(get());</code>.</p>
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</blockquote>
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<h3><a name="assignment">assignment</a></h3>
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<pre>intrusive_ptr & operator=(intrusive_ptr const & r);
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template<class Y> intrusive_ptr & operator=(intrusive_ptr<Y> const & r);
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intrusive_ptr & operator=(T * r);</pre>
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<blockquote>
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<p><b>Effects:</b> Equivalent to <code>intrusive_ptr(r).swap(*this)</code>.</p>
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<p><b>Returns:</b> <code>*this</code>.</p>
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</blockquote>
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<h3><a name="reset">reset</a></h3>
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<pre>void reset();</pre>
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<blockquote>
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<p><b>Effects:</b> Equivalent to <code>intrusive_ptr().swap(*this)</code>.</p>
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</blockquote>
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<pre>void reset(T * r);</pre>
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<blockquote>
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<p><b>Effects:</b> Equivalent to <code>intrusive_ptr(r).swap(*this)</code>.</p>
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</blockquote>
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<pre>void reset(T * r, bool add_ref);</pre>
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<blockquote>
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<p><b>Effects:</b> Equivalent to <code>intrusive_ptr(r, add_ref).swap(*this)</code>.</p>
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</blockquote>
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<h3><a name="indirection">indirection</a></h3>
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<pre>T & operator*() const; // never throws</pre>
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<blockquote>
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<p><b>Requirements:</b> <code>get() != 0</code>.</p>
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<p><b>Returns:</b> <code>*get()</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<pre>T * operator->() const; // never throws</pre>
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<blockquote>
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<p><b>Requirements:</b> <code>get() != 0</code>.</p>
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<p><b>Returns:</b> <code>get()</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<h3><a name="get">get</a></h3>
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<pre>T * get() const; // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> the stored pointer.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<h3><a name="detach">detach</a></h3>
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<pre>T * detach(); // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> the stored pointer.</p>
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<p><b>Throws:</b> nothing.</p>
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<p><b>Postconditions:</b> <code>get() == 0</code>.</p>
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<p><b>Notes:</b> The returned pointer has an elevated reference count. This
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allows conversion of an <code>intrusive_ptr</code> back to a raw pointer,
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without the performance overhead of acquiring and dropping an extra
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reference. It can be viewed as the complement of the
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non-reference-incrementing constructor.</p>
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<p><b>Caution:</b> Using <code>detach</code> escapes the safety of automatic
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reference counting provided by <code>intrusive_ptr</code>. It should
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by used only where strictly necessary (such as when interfacing to an
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existing API), and when the implications are thoroughly understood.</p>
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</blockquote>
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<h3><a name="conversions">conversions</a></h3>
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<pre>operator <i>unspecified-bool-type</i> () const; // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> an unspecified value that, when used in boolean contexts, is
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equivalent to <code>get() != 0</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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<p><b>Notes:</b> This conversion operator allows <code>intrusive_ptr</code> objects to be
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used in boolean contexts, like <code>if (p && p->valid()) {}</code>.
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The actual target type is typically a pointer to a member function, avoiding
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many of the implicit conversion pitfalls.</p>
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</blockquote>
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<h3><a name="swap">swap</a></h3>
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<pre>void swap(intrusive_ptr & b); // never throws</pre>
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<blockquote>
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<p><b>Effects:</b> Exchanges the contents of the two smart pointers.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<h2><a name="functions">Free Functions</a></h2>
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<h3><a name="comparison">comparison</a></h3>
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<pre>template<class T, class U>
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bool operator==(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b); // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> <code>a.get() == b.get()</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<pre>template<class T, class U>
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bool operator!=(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b); // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> <code>a.get() != b.get()</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<pre>template<class T, class U>
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bool operator==(intrusive_ptr<T> const & a, U * b); // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> <code>a.get() == b</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<pre>template<class T, class U>
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bool operator!=(intrusive_ptr<T> const & a, U * b); // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> <code>a.get() != b</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<pre>template<class T, class U>
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bool operator==(T * a, intrusive_ptr<U> const & b); // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> <code>a == b.get()</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<pre>template<class T, class U>
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bool operator!=(T * a, intrusive_ptr<U> const & b); // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> <code>a != b.get()</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<pre>template<class T, class U>
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bool operator<(intrusive_ptr<T> const & a, intrusive_ptr<U> const & b); // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> <code>std::less<T *>()(a.get(), b.get())</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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<p><b>Notes:</b> Allows <code>intrusive_ptr</code> objects to be used as keys
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in associative containers.</p>
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</blockquote>
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<h3><a name="free-swap">swap</a></h3>
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<pre>template<class T>
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void swap(intrusive_ptr<T> & a, intrusive_ptr<T> & b); // never throws</pre>
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<blockquote>
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<p><b>Effects:</b> Equivalent to <code>a.swap(b)</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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<p><b>Notes:</b> Matches the interface of <code>std::swap</code>. Provided as an aid to
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generic programming.</p>
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</blockquote>
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<h3><a name="get_pointer">get_pointer</a></h3>
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<pre>template<class T>
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T * get_pointer(intrusive_ptr<T> const & p); // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> <code>p.get()</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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<p><b>Notes:</b> Provided as an aid to generic programming. Used by <a href="../bind/mem_fn.html">
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mem_fn</a>.</p>
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</blockquote>
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<h3><a name="static_pointer_cast">static_pointer_cast</a></h3>
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<pre>template<class T, class U>
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intrusive_ptr<T> static_pointer_cast(intrusive_ptr<U> const & r); // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> <code>intrusive_ptr<T>(static_cast<T*>(r.get()))</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<h3><a name="const_pointer_cast">const_pointer_cast</a></h3>
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<pre>template<class T, class U>
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intrusive_ptr<T> const_pointer_cast(intrusive_ptr<U> const & r); // never throws</pre>
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<blockquote>
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<p><b>Returns:</b> <code>intrusive_ptr<T>(const_cast<T*>(r.get()))</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<h3><a name="dynamic_pointer_cast">dynamic_pointer_cast</a></h3>
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<pre>template<class T, class U>
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intrusive_ptr<T> dynamic_pointer_cast(intrusive_ptr<U> const & r);</pre>
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<blockquote>
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<p><b>Returns:</b> <code>intrusive_ptr<T>(dynamic_cast<T*>(r.get()))</code>.</p>
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<p><b>Throws:</b> nothing.</p>
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</blockquote>
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<h3><a name="insertion-operator">operator<<</a></h3>
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<pre>template<class E, class T, class Y>
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std::basic_ostream<E, T> & operator<< (std::basic_ostream<E, T> & os, intrusive_ptr<Y> const & p);</pre>
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<blockquote>
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<p><b>Effects:</b> <code>os << p.get();</code>.</p>
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<p><b>Returns:</b> <code>os</code>.</p>
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</blockquote>
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<hr>
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<p>$Date$</p>
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<p>
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<small>Copyright © 2003-2005, 2013 Peter Dimov. Distributed under the Boost Software License, Version
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1.0. See accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
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copy at <a href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>.</small></p>
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</body>
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</html>
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