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<title>Class template slot</title>
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<div class="refentry">
<a name="boost.signals2.slot"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Class template slot</span></h2>
<p>boost::signals2::slot — Pass slots as function arguments, and associate tracked objects with a slot.</p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: <<a class="link" href="../../signals2/reference.html#header.boost.signals2.slot_hpp" title="Header <boost/signals2/slot.hpp>">boost/signals2/slot.hpp</a>>
</span><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Signature<span class="special">,</span>
<span class="keyword">typename</span> SlotFunction <span class="special">=</span> <a class="link" href="../function.html" title="Class template function">boost::function</a><span class="special"><</span><span class="identifier">R</span> <span class="special">(</span><span class="identifier">T1</span><span class="special">,</span> <span class="identifier">T2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">TN</span><span class="special">)</span><span class="special">></span> <span class="special">></span>
<span class="keyword">class</span> <a class="link" href="slot.html" title="Class template slot">slot</a> <span class="special">:</span> <span class="keyword">public</span> <a class="link" href="slot_base.html" title="Class slot_base">boost::signals2::slot_base</a> <span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="comment">// types</span>
<span class="keyword">typedef</span> <span class="identifier">R</span> <a name="boost.signals2.slot.result_type"></a><span class="identifier">result_type</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">T1</span> <a name="boost.signals2.slot.argument_type"></a><span class="identifier">argument_type</span><span class="special">;</span> <span class="comment">// Exists iff arity == 1</span>
<span class="keyword">typedef</span> <span class="identifier">T1</span> <a name="boost.signals2.slot.first_argument_type"></a><span class="identifier">first_argument_type</span><span class="special">;</span> <span class="comment">// Exists iff arity == 2</span>
<span class="keyword">typedef</span> <span class="identifier">T2</span> <a name="boost.signals2.slot.second_argument_type"></a><span class="identifier">second_argument_type</span><span class="special">;</span> <span class="comment">// Exists iff arity == 2</span>
<span class="keyword">typedef</span> <span class="identifier">Signature</span> <a name="boost.signals2.slot.signature_type"></a><span class="identifier">signature_type</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">SlotFunction</span> <a name="boost.signals2.slot.slot_function_type"></a><span class="identifier">slot_function_type</span><span class="special">;</span>
<span class="comment">// static constants</span>
<span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">arity</span> = <span class="identifier">N</span><span class="special">;</span> <span class="comment">// The number of arguments taken by the slot.</span>
<span class="comment">// member classes/structs/unions</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">unsigned</span> n<span class="special">></span>
<span class="keyword">class</span> <a class="link" href="slot/arg.html" title="Class template arg">arg</a> <span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="comment">// types</span>
<span class="keyword">typedef</span> <span class="identifier">Tn</span> <a class="link" href="slot/arg.html#boost.signals2.slot.arg.type"><span class="identifier">type</span></a><span class="special">;</span> <span class="comment">// The type of the <a class="link" href="slot.html" title="Class template slot">slot</a>'s (n+1)th argument</span>
<span class="special">}</span><span class="special">;</span>
<span class="comment">// <a class="link" href="slot.html#boost.signals2.slotconstruct-copy-destruct">construct/copy/destruct</a></span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Slot<span class="special">></span> <a class="link" href="slot.html#idp94572920-bb"><span class="identifier">slot</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Slot</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> OtherSignature<span class="special">,</span> <span class="keyword">typename</span> OtherSlotFunction<span class="special">></span>
<a class="link" href="slot.html#idp94055208-bb"><span class="identifier">slot</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">slot</span><span class="special"><</span><span class="identifier">OtherSignature</span><span class="special">,</span> <span class="identifier">OtherSlotFunction</span><span class="special">></span> <span class="special">&</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Func<span class="special">,</span> <span class="keyword">typename</span> Arg1<span class="special">,</span> <span class="keyword">typename</span> Arg2<span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="keyword">typename</span> ArgN<span class="special">></span>
<a class="link" href="slot.html#idp94577496-bb"><span class="identifier">slot</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Func</span> <span class="special">&</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Arg1</span> <span class="special">&</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Arg2</span> <span class="special">&</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">ArgN</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span>
<span class="comment">// <a class="link" href="slot.html#idp96139896-bb">invocation</a></span>
<span class="identifier">result_type</span> <a class="link" href="slot.html#idp96140376-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="identifier">arg</span><span class="special"><</span><span class="number">0</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span><span class="special">,</span> <span class="identifier">arg</span><span class="special"><</span><span class="number">1</span><span class="special">></span><span class="special">::</span><span class="identifier">_type</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">arg</span><span class="special"><</span><span class="identifier">N</span><span class="special">-</span><span class="number">1</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span><span class="special">)</span><span class="special">;</span>
<span class="identifier">result_type</span> <a class="link" href="slot.html#idp96691752-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="identifier">arg</span><span class="special"><</span><span class="number">0</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span><span class="special">,</span> <span class="identifier">arg</span><span class="special"><</span><span class="number">1</span><span class="special">></span><span class="special">::</span><span class="identifier">_type</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">arg</span><span class="special"><</span><span class="identifier">N</span><span class="special">-</span><span class="number">1</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="comment">// <a class="link" href="slot.html#idp58467384-bb">tracking</a></span>
<span class="identifier">slot</span> <span class="special">&</span> <a class="link" href="slot.html#idp58467864-bb"><span class="identifier">track</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">weak_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> <span class="special">&</span><span class="special">)</span><span class="special">;</span>
<span class="identifier">slot</span> <span class="special">&</span> <a class="link" href="slot.html#idp93106248-bb"><span class="identifier">track</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="signal_base.html" title="Class signal_base">signals2::signal_base</a> <span class="special">&</span><span class="special">)</span><span class="special">;</span>
<span class="identifier">slot</span> <span class="special">&</span> <a class="link" href="slot.html#idp93107320-bb"><span class="identifier">track</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="slot_base.html" title="Class slot_base">signals2::slot_base</a> <span class="special">&</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> ForeignWeakPtr<span class="special">></span>
<span class="identifier">slot</span> <span class="special">&</span> <a class="link" href="slot.html#idp93289048-bb"><span class="identifier">track_foreign</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">ForeignWeakPtr</span> <span class="special">&</span><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">weak_ptr_traits</span><span class="special"><</span><span class="identifier">ForeignWeakPtr</span><span class="special">></span><span class="special">::</span><span class="identifier">shared_type</span> <span class="special">*</span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> ForeignSharedPtr<span class="special">></span>
<span class="identifier">slot</span> <span class="special">&</span> <a class="link" href="slot.html#idp93291112-bb"><span class="identifier">track_foreign</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">ForeignSharedPtr</span> <span class="special">&</span><span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">shared_ptr_traits</span><span class="special"><</span><span class="identifier">ForeignSharedPtr</span><span class="special">></span><span class="special">::</span><span class="identifier">weak_type</span> <span class="special">*</span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span>
<span class="comment">// <a class="link" href="slot.html#idp101634136-bb">slot function access</a></span>
<span class="identifier">slot_function_type</span> <span class="special">&</span> <a class="link" href="slot.html#idp101634568-bb"><span class="identifier">slot_function</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">const</span> <span class="identifier">slot_function_type</span> <span class="special">&</span> <a class="link" href="slot.html#idp101634952-bb"><span class="identifier">slot_function</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idp206256712"></a><h2>Description</h2>
<p>A slot consists of a polymorphic function wrapper (<a class="link" href="../function.html" title="Class template function">boost::function</a> by default)
plus a container of <code class="computeroutput">weak_ptr</code>s which identify the slot's "tracked objects". If any of the
tracked objects expire, the slot will automatically disable itself. That is, the slot's function
call operator will throw an exception instead of forwarding the function call to the slot's
polymorphic function wrapper. Additionally, a slot will automatically lock all the tracked objects
as <code class="computeroutput">shared_ptr</code> during invocation, to prevent any of them from expiring while
the polymorphic function wrapper is being run.
</p>
<p>
The slot constructor will search for <a class="link" href="signal.html" title="Class template signal">signals2::signal</a> and
<a class="link" href="trackable.html" title="Class trackable">signals2::trackable</a> inside incoming function objects and
automatically track them. It does so by applying a visitor
to the incoming functors with <a class="link" href="../visit_each.html" title="Function template visit_each">boost::visit_each</a>.
</p>
<div class="refsect2">
<a name="idp206260792"></a><h3>Template Parameters</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><span class="keyword">typename</span> Signature</pre>
<p></p>
</li>
<li class="listitem"><pre class="literallayout"><span class="keyword">typename</span> SlotFunction <span class="special">=</span> <a class="link" href="../function.html" title="Class template function">boost::function</a><span class="special"><</span><span class="identifier">R</span> <span class="special">(</span><span class="identifier">T1</span><span class="special">,</span> <span class="identifier">T2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">TN</span><span class="special">)</span><span class="special">></span></pre></li>
</ol></div>
</div>
<div class="refsect2">
<a name="idp206267016"></a><h3>
<a name="boost.signals2.slotconstruct-copy-destruct"></a><code class="computeroutput">slot</code>
public
construct/copy/destruct</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Slot<span class="special">></span> <a name="idp94572920-bb"></a><span class="identifier">slot</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Slot</span> <span class="special">&</span> target<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Effects:</span></p></td>
<td>
<p>Initializes the <code class="computeroutput">SlotFunction</code> object in <code class="computeroutput">this</code>
with <code class="computeroutput">target</code>, which may be any
function object with which a
<code class="computeroutput">SlotFunction</code> can be
constructed.
</p>
<p>In this special case where the template type parameter <code class="computeroutput">Slot</code> is
a compatible <a class="link" href="signal.html" title="Class template signal">signals2::signal</a> type,
the signal will automatically be added to the slot's tracked object list.
Otherwise, the slot's tracked object list is initially empty.
</p>
</td>
</tr></tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> OtherSignature<span class="special">,</span> <span class="keyword">typename</span> OtherSlotFunction<span class="special">></span>
<a name="idp94055208-bb"></a><span class="identifier">slot</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">slot</span><span class="special"><</span><span class="identifier">OtherSignature</span><span class="special">,</span> <span class="identifier">OtherSlotFunction</span><span class="special">></span> <span class="special">&</span> other_slot<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Effects:</span></p></td>
<td><p>Initializes <code class="computeroutput">this</code> with a copy of
<code class="computeroutput">other_slot</code>'s <code class="computeroutput">OtherSlotFunction</code> object and tracked object list.
</p></td>
</tr></tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> Func<span class="special">,</span> <span class="keyword">typename</span> Arg1<span class="special">,</span> <span class="keyword">typename</span> Arg2<span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="keyword">typename</span> ArgN<span class="special">></span>
<a name="idp94577496-bb"></a><span class="identifier">slot</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Func</span> <span class="special">&</span> f<span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Arg1</span> <span class="special">&</span> a1<span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Arg2</span> <span class="special">&</span> a2<span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">ArgN</span> <span class="special">&</span> aN<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Effects:</span></p></td>
<td><p>Syntactic sugar for <code class="computeroutput">bind()</code> when the constructor is passed more than
one argument. As if:
<code class="computeroutput">slot(boost::bind(f, a1, a2, ..., aN))</code>
</p></td>
</tr></tbody>
</table></div>
</li>
</ol></div>
</div>
<div class="refsect2">
<a name="idp206296344"></a><h3>
<a name="idp96139896-bb"></a><code class="computeroutput">slot</code> invocation</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<pre class="literallayout"><a name="idp96140136-bb"></a><span class="identifier">result_type</span> <a name="idp96140376-bb"></a><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="identifier">arg</span><span class="special"><</span><span class="number">0</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span> a1<span class="special">,</span> <span class="identifier">arg</span><span class="special"><</span><span class="number">1</span><span class="special">></span><span class="special">::</span><span class="identifier">_type</span> a2<span class="special">,</span> <span class="special">...</span><span class="special">,</span>
<span class="identifier">arg</span><span class="special"><</span><span class="identifier">N</span><span class="special">-</span><span class="number">1</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span> aN<span class="special">)</span><span class="special">;</span>
<span class="identifier">result_type</span> <a name="idp96691752-bb"></a><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span><span class="special">(</span><span class="identifier">arg</span><span class="special"><</span><span class="number">0</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span> a1<span class="special">,</span> <span class="identifier">arg</span><span class="special"><</span><span class="number">1</span><span class="special">></span><span class="special">::</span><span class="identifier">_type</span> a2<span class="special">,</span> <span class="special">...</span><span class="special">,</span>
<span class="identifier">arg</span><span class="special"><</span><span class="identifier">N</span><span class="special">-</span><span class="number">1</span><span class="special">></span><span class="special">::</span><span class="identifier">type</span> aN<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term">Effects:</span></p></td>
<td><p>Calls the slot's <code class="computeroutput">SlotFunction</code> object.
</p></td>
</tr>
<tr>
<td><p><span class="term">Returns:</span></p></td>
<td><p>The result returned by the slot's <code class="computeroutput">SlotFunction</code> object.</p></td>
</tr>
<tr>
<td><p><span class="term">Throws:</span></p></td>
<td><p>Any exceptions thrown by the slot's <code class="computeroutput">SlotFunction</code> object.
<a class="link" href="expired_slot.html" title="Class expired_slot">boost::signals2::expired_slot</a> if any object in the tracked object list
has expired.</p></td>
</tr>
<tr>
<td><p><span class="term">Notes:</span></p></td>
<td><p>If you have already used <a class="link" href="slot_base.html#idp60718520-bb">lock</a> to insure the
tracked objects are valid, it is slightly more efficient to use the
<a class="link" href="slot.html#idp101634328-bb">slot_function</a>() method
and call the slot's <code class="computeroutput">SlotFunction</code> directly.</p></td>
</tr>
</tbody>
</table></div>
</li></ol></div>
</div>
<div class="refsect2">
<a name="idp206321304"></a><h3>
<a name="idp58467384-bb"></a><code class="computeroutput">slot</code> tracking</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><a name="idp58467624-bb"></a><span class="identifier">slot</span> <span class="special">&</span> <a name="idp58467864-bb"></a><span class="identifier">track</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">weak_ptr</span><span class="special"><</span><span class="keyword">void</span><span class="special">></span> <span class="special">&</span> tracked_object<span class="special">)</span><span class="special">;</span>
<span class="identifier">slot</span> <span class="special">&</span> <a name="idp93106248-bb"></a><span class="identifier">track</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="signal_base.html" title="Class signal_base">signals2::signal_base</a> <span class="special">&</span> tracked_signal<span class="special">)</span><span class="special">;</span>
<span class="identifier">slot</span> <span class="special">&</span> <a name="idp93107320-bb"></a><span class="identifier">track</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="slot_base.html" title="Class slot_base">signals2::slot_base</a> <span class="special">&</span> tracked_slot<span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term">Effects:</span></p></td>
<td>
<p>
Adds object(s) to the slot's tracked object list. Should any of the
tracked objects expire, then subsequent attempts to call the slot's <code class="computeroutput">operator()</code>
or <code class="computeroutput">lock()</code> methods will throw an <a class="link" href="expired_slot.html" title="Class expired_slot">signals2::expired_slot</a> exception.
</p>
<p>When tracking a signal, a shared_ptr
internal to the signal class is used for tracking. The signal does not
need to be owned by an external <code class="computeroutput">shared_ptr</code>.
</p>
<p>
In the case of passing another slot as the argument to <code class="computeroutput">track()</code>,
only the objects currently in the other slot's tracked object list are added
to the tracked object list of <code class="computeroutput">this</code>. The other slot object itself
is not tracked.
</p>
</td>
</tr>
<tr>
<td><p><span class="term">Returns:</span></p></td>
<td><p><code class="computeroutput">*this</code></p></td>
</tr>
</tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><a name="idp93288856-bb"></a><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> ForeignWeakPtr<span class="special">></span>
<span class="identifier">slot</span> <span class="special">&</span> <a name="idp93289048-bb"></a><span class="identifier">track_foreign</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">ForeignWeakPtr</span> <span class="special">&</span> tracked_object<span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">weak_ptr_traits</span><span class="special"><</span><span class="identifier">ForeignWeakPtr</span><span class="special">></span><span class="special">::</span><span class="identifier">shared_type</span> <span class="special">*</span> SFINAE <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> ForeignSharedPtr<span class="special">></span>
<span class="identifier">slot</span> <span class="special">&</span> <a name="idp93291112-bb"></a><span class="identifier">track_foreign</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">ForeignSharedPtr</span> <span class="special">&</span> tracked_object<span class="special">,</span>
<span class="keyword">typename</span> <span class="identifier">shared_ptr_traits</span><span class="special"><</span><span class="identifier">ForeignSharedPtr</span><span class="special">></span><span class="special">::</span><span class="identifier">weak_type</span> <span class="special">*</span> SFINAE <span class="special">=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term">Effects:</span></p></td>
<td>
<p>
The <code class="computeroutput">track_foreign</code>() method behaves similarly to calling the <a class="link" href="slot.html#idp58467624-bb">track</a>() method
with a boost::shared_ptr or boost::weak_ptr argument.
However, <code class="computeroutput">track_foreign</code> is more flexible in that it will accept <code class="computeroutput">shared_ptr</code>
or <code class="computeroutput">weak_ptr</code> classes from outside of boost (most significantly <code class="computeroutput">std::shared_ptr</code>
or <code class="computeroutput">std::weak_ptr</code>).
</p>
<p>
In order to use a particular <code class="computeroutput">shared_ptr</code> class with this function, a specialization of
boost::signals2::shared_ptr_traits must exist for it.
Also, a specialization of boost::signals2::weak_ptr_traits must
be provided for its corresponding <code class="computeroutput">weak_ptr</code> class.
The <code class="computeroutput">shared_ptr_traits</code> specialization must include a <code class="computeroutput">weak_type</code>
member typedef which specifies the
corresponding <code class="computeroutput">weak_ptr</code> type of the <code class="computeroutput">shared_ptr</code> class.
Similarly, the <code class="computeroutput">weak_ptr_traits</code> specialization must include a <code class="computeroutput">shared_type</code>
member typedef which specifies the corresponding <code class="computeroutput">shared_ptr</code> type of the
<code class="computeroutput">weak_ptr</code> class. Specializations
for <code class="computeroutput">std::shared_ptr</code> and <code class="computeroutput">std::weak_ptr</code> are already provided by the signals2 library.
For other <code class="computeroutput">shared_ptr</code> classes, you must provide the specializations.
</p>
<p>The second argument "SFINAE" may be ignored, it is used to resolve the overload between
either <code class="computeroutput">shared_ptr</code> or <code class="computeroutput">weak_ptr</code> objects passed in as the first argument.
</p>
</td>
</tr>
<tr>
<td><p><span class="term">Returns:</span></p></td>
<td><p><code class="computeroutput">*this</code></p></td>
</tr>
</tbody>
</table></div>
</li>
</ol></div>
</div>
<div class="refsect2">
<a name="idp206364040"></a><h3>
<a name="idp101634136-bb"></a><code class="computeroutput">slot</code> slot function access</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<pre class="literallayout"><a name="idp101634328-bb"></a><span class="identifier">slot_function_type</span> <span class="special">&</span> <a name="idp101634568-bb"></a><span class="identifier">slot_function</span><span class="special">(</span><span class="special">)</span><span class="special">;</span>
<span class="keyword">const</span> <span class="identifier">slot_function_type</span> <span class="special">&</span> <a name="idp101634952-bb"></a><span class="identifier">slot_function</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Returns:</span></p></td>
<td><p>A reference to the slot's underlying SlotFunction object.</p></td>
</tr></tbody>
</table></div>
</li></ol></div>
</div>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2001-2004 Douglas Gregor<br>Copyright © 2007-2009 Frank Mori Hess<p>Distributed under the Boost
Software License, Version 1.0. (See accompanying file
<code class="filename">LICENSE_1_0.txt</code> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</p>
</div></td>
</tr></table>
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