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- <a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics____free_functions"></a><a class="link" href="detailed_semantics____free_functions.html" title="Detailed Semantics -- Free Functions">Detailed
- Semantics -- Free Functions</a>
- </h4></div></div></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_make_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">make_optional</span><span class="special">(</span>
- <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span>
- type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="number">1</span><span class="special">+</span><span class="number">1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Creates an optional<int></span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_make_optional_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="identifier">make_optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span>
- <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">condition</span><span class="special">,</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span>
- type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">calculate_foo</span><span class="special">()</span>
- <span class="special">{</span>
- <span class="keyword">double</span> <span class="identifier">val</span> <span class="special">=</span> <span class="identifier">compute_foo</span><span class="special">();</span>
- <span class="keyword">return</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="identifier">is_not_nan_and_finite</span><span class="special">(</span><span class="identifier">val</span><span class="special">),</span><span class="identifier">val</span><span class="special">);</span>
- <span class="special">}</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">calculate_foo</span><span class="special">();</span>
- <span class="keyword">if</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">v</span> <span class="special">)</span>
- <span class="identifier">error</span><span class="special">(</span><span class="string">"foo wasn't computed"</span><span class="special">);</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_operator_compare_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
- <span class="special">==</span> <span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
- shall meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> If both <code class="computeroutput"><span class="identifier">x</span></code>
- and <code class="computeroutput"><span class="identifier">y</span></code> are initialized,
- <code class="computeroutput"><span class="special">(*</span><span class="identifier">x</span>
- <span class="special">==</span> <span class="special">*</span><span class="identifier">y</span><span class="special">)</span></code>.
- If only <code class="computeroutput"><span class="identifier">x</span></code> or <code class="computeroutput"><span class="identifier">y</span></code> is initialized, <code class="computeroutput"><span class="keyword">false</span></code>.
- If both are uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> This definition guarantees
- that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
- not containing a value is compared unequal to any <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> containing any value, and equal
- to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> not containing a value. Pointers
- have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code>
- has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code> directly in generic code which expect
- to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#equal" target="_top"><code class="computeroutput"><span class="identifier">equal_pointees</span><span class="special">()</span></code></a>
- instead
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">)),</span> <span class="identifier">o1_</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o2</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">));</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN</span> <span class="special">);</span> <span class="comment">// Identity implies equality</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1</span> <span class="special">);</span> <span class="comment">//</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN_</span> <span class="special">);</span> <span class="comment">// Both uninitialized compare equal</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">!=</span> <span class="identifier">o1</span> <span class="special">);</span> <span class="comment">// Initialized unequal to initialized.</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1_</span> <span class="special">);</span> <span class="comment">// Both initialized compare as (*lhs == *rhs)</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">!=</span> <span class="identifier">o2</span> <span class="special">);</span> <span class="comment">//</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_operator_compare_less_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
- <span class="special"><</span> <span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> Expression <code class="computeroutput"><span class="special">*</span><span class="identifier">x</span> <span class="special"><</span> <span class="special">*</span><span class="identifier">y</span></code> shall be well-formed and its result
- shall be convertible to <code class="computeroutput"><span class="keyword">bool</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">(!</span><span class="identifier">y</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">false</span> <span class="special">:</span> <span class="special">(!</span><span class="identifier">x</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">true</span> <span class="special">:</span> <span class="special">*</span><span class="identifier">x</span> <span class="special"><</span>
- <span class="special">*</span><span class="identifier">y</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> This definition guarantees
- that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
- not containing a value is ordered as less than any <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> containing any value, and equivalent
- to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> not containing a value. Pointers
- have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code>
- has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code> directly in generic code which
- expect to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#less" target="_top"><code class="computeroutput"><span class="identifier">less_pointees</span><span class="special">()</span></code></a>
- instead. <code class="computeroutput"><span class="identifier">T</span></code> need not
- be <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>. Only
- single <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code>
- is required. Other relational operations are defined in terms of this
- one. If <code class="computeroutput"><span class="identifier">T</span></code>'s <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code>
- satisfies the axioms of <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a> (transitivity,
- antisymmetry and irreflexivity), <code class="computeroutput"><span class="identifier">optinal</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o0</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">0</span><span class="special">));</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Identity implies equivalence</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o1</span> <span class="special"><</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">oN_</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Two uninitialized are equivalent</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN_</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">o0</span> <span class="special">);</span> <span class="comment">// Uninitialized is less than initialized</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o0</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special"><</span> <span class="identifier">o2</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Two initialized compare as (*lhs < *rhs)</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special"><</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special"><</span> <span class="identifier">o2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_operator_compare_not_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
- <span class="special">!=</span> <span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
- <span class="identifier">x</span> <span class="special">==</span>
- <span class="identifier">y</span> <span class="special">);</span></code>
- </li></ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_operator_compare_greater_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
- <span class="special">></span> <span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">(</span>
- <span class="identifier">y</span> <span class="special"><</span>
- <span class="identifier">x</span> <span class="special">);</span></code>
- </li></ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_operator_compare_less_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
- <span class="special"><=</span> <span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
- <span class="identifier">y</span> <span class="special"><</span>
- <span class="identifier">x</span> <span class="special">);</span></code>
- </li></ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_operator_compare_greater_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
- <span class="special">>=</span> <span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
- <span class="identifier">x</span> <span class="special"><</span>
- <span class="identifier">y</span> <span class="special">);</span></code>
- </li></ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_operator_compare_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
- <span class="special">==</span> <span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span>
- <span class="keyword">noexcept</span><span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
- <span class="special">==</span> <span class="special">(</span>
- <span class="identifier">none_t</span><span class="special">,</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">!</span><span class="identifier">x</span></code>.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
- need not meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>.
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_operator_compare_not_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
- <span class="special">!=</span> <span class="special">(</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span>
- <span class="keyword">noexcept</span><span class="special">;</span></code>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
- <span class="special">!=</span> <span class="special">(</span>
- <span class="identifier">none_t</span><span class="special">,</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
- <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
- <span class="identifier">x</span> <span class="special">==</span>
- <span class="identifier">y</span> <span class="special">);</span></code>
- </li></ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_swap_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
- <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">y</span>
- <span class="special">)</span> <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Requires:</strong></span> Lvalues of type <code class="computeroutput"><span class="identifier">T</span></code> shall be swappable and <code class="computeroutput"><span class="identifier">T</span></code> shall be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>.
- </li>
- <li class="listitem">
- <p class="simpara">
- <span class="bold"><strong>Effects:</strong></span>
- </p>
- <div class="informaltable"><table class="table">
- <colgroup>
- <col>
- <col>
- <col>
- </colgroup>
- <thead><tr></tr></thead>
- <tbody>
- <tr>
- <td>
- </td>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
- contains a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- calls <code class="computeroutput"><span class="identifier">swap</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">),</span> <span class="special">*</span><span class="identifier">rhs</span><span class="special">)</span></code>
- </p>
- </td>
- <td>
- <p>
- initializes the contained value of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> as if direct-initializing
- an object of type <code class="computeroutput"><span class="identifier">T</span></code>
- with the expression <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>, followed by <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>,
- <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
- contains a value and <code class="computeroutput"><span class="identifier">rhs</span></code>
- does not contain a value
- </p>
- </td>
- </tr>
- <tr>
- <td>
- <p>
- <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
- does not contain a value</strong></span>
- </p>
- </td>
- <td>
- <p>
- initializes the contained value of <code class="computeroutput"><span class="identifier">rhs</span></code>
- as if direct-initializing an object of type <code class="computeroutput"><span class="identifier">T</span></code> with the expression
- <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">))</span></code>,
- followed by <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value
- and <code class="computeroutput"><span class="identifier">rhs</span></code> contains
- a value
- </p>
- </td>
- <td>
- <p>
- no effect
- </p>
- </td>
- </tr>
- </tbody>
- </table></div>
- </li>
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> The states of <code class="computeroutput"><span class="identifier">x</span></code> and <code class="computeroutput"><span class="identifier">y</span></code>
- interchanged.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Throws:</strong></span> If both are initialized, whatever
- <code class="computeroutput"><span class="identifier">swap</span><span class="special">(</span><span class="identifier">T</span><span class="special">&,</span><span class="identifier">T</span><span class="special">&)</span></code>
- throws. If only one is initialized, whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
- throws.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
- <span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def0</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def1</span> <span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optX</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optY</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
- <span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">def1</span><span class="special">);</span> <span class="comment">// no-op</span>
- <span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def0</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
- <span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span> <span class="comment">// Get back to original values</span>
- <span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span><span class="identifier">optY</span><span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optX</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optY</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
- </pre>
- </li>
- </ul></div>
- <p>
- <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
- </p>
- <a name="reference_swap_optional_reference"></a><div class="blockquote"><blockquote class="blockquote"><p>
- <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
- <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span> <span class="identifier">y</span>
- <span class="special">)</span> <span class="keyword">noexcept</span>
- <span class="special">;</span></code>
- </p></blockquote></div>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="identifier">x</span></code>
- refers to what <code class="computeroutput"><span class="identifier">y</span></code> refererred
- to before the swap (if anything). <code class="computeroutput"><span class="identifier">y</span></code>
- refers to whatever <code class="computeroutput"><span class="identifier">x</span></code>
- referred to before the swap.
- </li>
- <li class="listitem">
- <span class="bold"><strong>Example:</strong></span>
- <pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
- <span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt0</span><span class="special">;</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">optX</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
- <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">optY</span> <span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
- <span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span> <span class="identifier">optY</span><span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optX</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
- <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optY</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">x</span><span class="special">));</span>
- <span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">,</span> <span class="identifier">optX</span><span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
- <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
- </pre>
- [endsect]
- </li>
- </ul></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 © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p>
- Distributed under the Boost Software License, Version 1.0. (See accompanying
- file LICENSE_1_0.txt 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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