1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Macro BOOST_CONTRACT_CONSTRUCTOR_PRECONDITION</title> 5<link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="index.html" title="Chapter 1. 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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> 38<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">u</span> 39 <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"><</span><span class="identifier">u</span><span class="special">></span><span class="special">,</span> \ 40 <span class="keyword">public</span> <span class="identifier">b</span> 41 <span class="special">:</span> <span class="identifier">BASES</span> 42<span class="special">{</span> 43 <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> 44 45 <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> 46 <span class="preprocessor">#undef</span> <span class="identifier">BASES</span> 47 48 <span class="special">...</span> 49 50<span class="keyword">public</span><span class="special">:</span> 51 <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> 52 <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">&</span><span class="special">]</span> <span class="special">{</span> 53 <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> 54 <span class="special">}</span><span class="special">)</span><span class="special">,</span> 55 <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> 56 <span class="special">{</span> 57 <span class="special">...</span> 58 <span class="special">}</span> 59 60 <span class="special">...</span> 61<span class="special">}</span><span class="special">;</span> 62</pre> 63<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_idm46268585474880.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> 64<pre class="programlisting"><span class="comment">// Guarded only by NO_PRECONDITIONS (and not also by NO_CONSTRUCTORS)</span> 65<span class="comment">// because for constructor's preconditions (not for postconditions, etc.).</span> 66<span class="preprocessor">#ifndef</span> <span class="identifier">BOOST_CONTRACT_NO_PRECONDITIONS</span> 67 <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"><</span><span class="identifier">class_type</span><span class="special">></span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span> 68<span class="preprocessor">#else</span> <span class="comment">// No-op call (likely optimized away, minimal to no overhead).</span> 69 <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"><</span><span class="identifier">class_type</span><span class="special">></span><span class="special">(</span><span class="special">)</span> 70<span class="preprocessor">#endif</span> 71</pre> 72<p>Where:</p> 73<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 74<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> 75<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> 76</ul></div> 77<p> 78</p> 79<p><span class="bold"><strong>See Also:</strong></span></p> 80<p> <a class="link" href="boost_contract/extras.html#boost_contract.extras.disable_contract_compilation__macro_interface_" title="Disable Contract Compilation (Macro Interface)"> 81 Disable Contract Compilation</a>, <a class="link" href="boost_contract/tutorial.html#boost_contract.tutorial.constructors" title="Constructors"> Constructors</a> </p> 82<p> 83</p> 84<p> 85</p> 86</div> 87</div> 88<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 89<td align="left"></td> 90<td align="right"><div class="copyright-footer">Copyright © 2008-2019 Lorenzo Caminiti<p> 91 Distributed under the Boost Software License, Version 1.0 (see accompanying 92 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>) 93 </p> 94</div></td> 95</tr></table> 96<hr> 97<div class="spirit-nav"> 98<a accesskey="p" href="BOOST_CONTRACT_CONSTRUCTOR.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="reference.html#header.boost.contract_macro_hpp"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="index.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="BOOST_CONTRACT_DESTRUCTOR.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 99</div> 100</body> 101</html> 102
