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<h2><span class="refentrytitle">Macro BOOST_CONTRACT_CONSTRUCTOR_PRECONDITION</span></h2>
<p>BOOST_CONTRACT_CONSTRUCTOR_PRECONDITION — Program preconditions that can be disabled at compile-time for constructors. </p>
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<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: &lt;<a class="link" href="reference.html#header.boost.contract_macro_hpp" title="Header &lt;boost/contract_macro.hpp&gt;">boost/contract_macro.hpp</a>&gt;
</span>BOOST_CONTRACT_CONSTRUCTOR_PRECONDITION(...)</pre></div>
<div class="refsect1">
<a name="idm45909316234208"></a><h2>Description</h2>
<p>This is used together with <code class="computeroutput"><a class="link" href="BOOST_CONTRACT_CONSTRUCTOR.html" title="Macro BOOST_CONTRACT_CONSTRUCTOR">BOOST_CONTRACT_CONSTRUCTOR</a></code> to specify contracts for constructors. Constructors that do not have preconditions do not use this macro. When at least one of the class constructors uses this macro, <code class="computeroutput"><a class="link" href="boost/contract/constructor_precondition.html" title="Class template constructor_precondition">boost::contract::constructor_precondition</a></code> must be the first and private base of the class declaring the constructor for which preconditions are programmed:</p>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">u</span>
<span class="preprocessor">#define</span> <span class="identifier">BASES</span> <span class="keyword">private</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">constructor_precondition</span><span class="special">&lt;</span><span class="identifier">u</span><span class="special">&gt;</span><span class="special">,</span> \
<span class="keyword">public</span> <span class="identifier">b</span>
<span class="special">:</span> <span class="identifier">BASES</span>
<span class="special">{</span>
<span class="keyword">friend</span> <span class="keyword">class</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">access</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">BOOST_CONTRACT_BASE_TYPES</span><span class="special">(</span><span class="identifier">BASES</span><span class="special">)</span> <span class="identifier">base_types</span><span class="special">;</span>
<span class="preprocessor">#undef</span> <span class="identifier">BASES</span>
<span class="special">...</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="keyword">explicit</span> <span class="identifier">u</span><span class="special">(</span><span class="keyword">unsigned</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">:</span>
<span class="identifier">BOOST_CONTRACT_CONSTRUCTOR_PRECONDITION</span><span class="special">(</span><span class="identifier">u</span><span class="special">)</span><span class="special">(</span><span class="special">[</span><span class="special">&amp;</span><span class="special">]</span> <span class="special">{</span>
<span class="identifier">BOOST_CONTRACT_ASSERT</span><span class="special">(</span><span class="identifier">x</span> <span class="special">!=</span> <span class="number">0</span><span class="special">)</span><span class="special">;</span>
<span class="special">}</span><span class="special">)</span><span class="special">,</span>
<span class="identifier">b</span><span class="special">(</span><span class="number">1</span> <span class="special">/</span> <span class="identifier">x</span><span class="special">)</span>
<span class="special">{</span>
<span class="special">...</span>
<span class="special">}</span>
<span class="special">...</span>
<span class="special">}</span><span class="special">;</span>
</pre>
<p><code class="computeroutput">BOOST_CONTRACT_CONSTRUCTOR_PRECONDITION(class_type)(f)</code> expands to code equivalent to the following (note that when <code class="computeroutput"><a class="link" href="BOOST_CO_idm45028039660048.html" title="Macro BOOST_CONTRACT_NO_PRECONDITIONS">BOOST_CONTRACT_NO_PRECONDITIONS</a></code> is defined, this macro trivially expands to a default constructor call that is internally implemented to do nothing so this should have minimal to no overhead):</p>
<pre class="programlisting"><span class="comment">// Guarded only by NO_PRECONDITIONS (and not also by NO_CONSTRUCTORS)</span>
<span class="comment">// because for constructor's preconditions (not for postconditions, etc.).</span>
<span class="preprocessor">#ifndef</span> <span class="identifier">BOOST_CONTRACT_NO_PRECONDITIONS</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">constructor_precondition</span><span class="special">&lt;</span><span class="identifier">class_type</span><span class="special">&gt;</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span>
<span class="preprocessor">#else</span> <span class="comment">// No-op call (likely optimized away, minimal to no overhead).</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">constructor_precondition</span><span class="special">&lt;</span><span class="identifier">class_type</span><span class="special">&gt;</span><span class="special">(</span><span class="special">)</span>
<span class="preprocessor">#endif</span>
</pre>
<p>Where:</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p><code class="computeroutput"><span class="bold"><strong>class_type</strong></span></code> is the type of the class containing the constructor for which preconditions are being programmed. (This is a variadic macro parameter so it can contain commas not protected by round parenthesis.) </p></li>
<li class="listitem"><p><code class="computeroutput"><span class="bold"><strong>f</strong></span></code> is the nullary functor called by this library to check constructor preconditions <code class="computeroutput">f()</code>. Assertions within this functor call are usually programmed using <code class="computeroutput"><a class="link" href="BOOST_CONTRACT_ASSERT.html" title="Macro BOOST_CONTRACT_ASSERT">BOOST_CONTRACT_ASSERT</a></code>, but any exception thrown by a call to this functor indicates a contract failure (and will result in this library calling <code class="computeroutput"><a class="link" href="boost/contract/precondition_failure.html" title="Function precondition_failure">boost::contract::precondition_failure</a></code>). This functor should capture variables by (constant) value, or better by (constant) reference to avoid extra copies. (This is a variadic macro parameter so it can contain commas not protected by round parenthesis.)</p></li>
</ul></div>
<p>
</p>
<p><span class="bold"><strong>See Also:</strong></span></p>
<p> <a class="link" href="boost_contract/extras.html#boost_contract.extras.disable_contract_compilation__macro_interface_" title="Disable Contract Compilation (Macro Interface)">
Disable Contract Compilation</a>, <a class="link" href="boost_contract/tutorial.html#boost_contract.tutorial.constructors" title="Constructors"> Constructors</a> </p>
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<td align="right"><div class="copyright-footer">Copyright © 2008-2019 Lorenzo Caminiti<p>
Distributed under the Boost Software License, Version 1.0 (see accompanying
file LICENSE_1_0.txt or a copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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