123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320 |
- <html>
- <head>
- <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
- <title>Chapter 1. Boost.Contract 1.0.0</title>
- <link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css">
- <meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
- <link rel="home" href="index.html" title="Chapter 1. Boost.Contract 1.0.0">
- <link rel="next" href="boost_contract/full_table_of_contents.html" title="Full Table of Contents">
- </head>
- <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
- <table cellpadding="2" width="100%"><tr>
- <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td>
- <td align="center"><a href="../../../../index.html">Home</a></td>
- <td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td>
- <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
- <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
- <td align="center"><a href="../../../../more/index.htm">More</a></td>
- </tr></table>
- <hr>
- <div class="spirit-nav"><a accesskey="n" href="boost_contract/full_table_of_contents.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a></div>
- <div class="chapter">
- <div class="titlepage"><div>
- <div><h2 class="title">
- <a name="boost_contract"></a>Chapter 1. Boost.Contract 1.0.0</h2></div>
- <div><div class="author"><h3 class="author">
- <span class="firstname">Lorenzo</span> <span class="surname">Caminiti <code class="email"><<a class="email" href="mailto:lorcaminiti@gmail.com">lorcaminiti@gmail.com</a>></code></span>
- </h3></div></div>
- <div><p class="copyright">Copyright © 2008-2019 Lorenzo Caminiti</p></div>
- <div><div class="legalnotice">
- <a name="boost_contract.legal"></a><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>)
- </p>
- </div></div>
- </div></div>
- <div class="toc">
- <p><b>Table of Contents</b></p>
- <dl class="toc">
- <dt><span class="section"><a href="index.html#boost_contract.introduction">Introduction</a></span></dt>
- <dt><span class="section"><a href="boost_contract/full_table_of_contents.html">Full Table of Contents</a></span></dt>
- <dt><span class="section"><a href="boost_contract/getting_started.html">Getting Started</a></span></dt>
- <dt><span class="section"><a href="boost_contract/contract_programming_overview.html">Contract
- Programming Overview</a></span></dt>
- <dt><span class="section"><a href="boost_contract/tutorial.html">Tutorial</a></span></dt>
- <dt><span class="section"><a href="boost_contract/advanced.html">Advanced</a></span></dt>
- <dt><span class="section"><a href="boost_contract/extras.html">Extras</a></span></dt>
- <dt><span class="section"><a href="boost_contract/examples.html">Examples</a></span></dt>
- <dt><span class="section"><a href="reference.html">Reference</a></span></dt>
- <dt><span class="section"><a href="boost_contract/release_notes.html">Release Notes</a></span></dt>
- <dt><span class="section"><a href="boost_contract/bibliography.html">Bibliography</a></span></dt>
- <dt><span class="section"><a href="boost_contract/acknowledgments.html">Acknowledgments</a></span></dt>
- </dl>
- </div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <span class="emphasis"><em><span class="quote">“<span class="quote">Our field needs more formality, but the profession has not
- realized it yet.</span>”</span></em></span>
- </p></blockquote></div>
- <div class="blockquote"><blockquote class="blockquote"><p>
- <span class="emphasis"><em>-- Bertrand Meyer (see <a class="link" href="boost_contract/bibliography.html#Meyer97_anchor">[Meyer97]</a>
- page 400)</em></span>
- </p></blockquote></div>
- <p>
- This library implements <a href="http://en.wikipedia.org/wiki/Design_by_contract" target="_top">contract
- programming</a> (a.k.a., Design by Contract or DbC) <a href="#ftn.boost_contract.f0" class="footnote" name="boost_contract.f0"><sup class="footnote">[1]</sup></a> for the C++ programming language. All contract programming features
- are supported by this library: Subcontracting, class invariants (also for static
- and volatile member functions), postconditions (with old and return values),
- preconditions, customizable actions on assertion failure (e.g., terminate the
- program or throw exceptions), optional compilation of assertions, disable assertions
- while already checking other assertions (to avoid infinite recursion), and more
- (see <a class="link" href="boost_contract/contract_programming_overview.html#boost_contract.contract_programming_overview.feature_summary" title="Feature Summary">Feature
- Summary</a>).
- </p>
- <div class="section">
- <div class="titlepage"><div><div><h2 class="title" style="clear: both">
- <a name="boost_contract.introduction"></a><a class="link" href="index.html#boost_contract.introduction" title="Introduction">Introduction</a>
- </h2></div></div></div>
- <p>
- Contract programming allows to specify preconditions, postconditions, and class
- invariants that are automatically checked when functions are executed at run-time.
- These conditions assert program specifications within the source code itself
- allowing to find bugs more quickly during testing, making the code self-documenting,
- and increasing overall software quality (see <a class="link" href="boost_contract/contract_programming_overview.html" title="Contract Programming Overview">Contract
- Programming Overview</a>).
- </p>
- <p>
- For example, consider the following function <code class="computeroutput"><span class="identifier">inc</span></code>
- that increments its argument <code class="computeroutput"><span class="identifier">x</span></code>
- by <code class="computeroutput"><span class="number">1</span></code> and let's write its contract
- using code comments (see <a href="../../example/features/introduction_comments.cpp" target="_top"><code class="literal">introduction_comments.cpp</code></a>):
- </p>
- <p>
- </p>
- <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">inc</span><span class="special">(</span><span class="keyword">int</span><span class="special">&</span> <span class="identifier">x</span><span class="special">)</span>
- <span class="comment">// Precondition: x < std::numeric_limit<int>::max()</span>
- <span class="comment">// Postcondition: x == oldof(x) + 1</span>
- <span class="special">{</span>
- <span class="special">++</span><span class="identifier">x</span><span class="special">;</span> <span class="comment">// Function body.</span>
- <span class="special">}</span>
- </pre>
- <p>
- </p>
- <p>
- The precondition states that at function entry the argument <code class="computeroutput"><span class="identifier">x</span></code>
- must be strictly smaller than the maximum allowable value of its type (so it
- can be incremented by <code class="computeroutput"><span class="number">1</span></code> without
- overflowing). The postcondition states that at function exit the argument
- <code class="computeroutput"><span class="identifier">x</span></code> must be incremented by <code class="computeroutput"><span class="number">1</span></code> with respect to the <span class="emphasis"><em>old value</em></span>
- that <code class="computeroutput"><span class="identifier">x</span></code> had before executing
- the function (indicated here by <code class="literal"><span class="emphasis"><em>oldof</em></span></code><code class="computeroutput"><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code>).
- Note that postconditions shall be checked only when the execution of the function
- body does not throw an exception.
- </p>
- <p>
- Now let's program this function and its contract using this library (see <a href="../../example/features/introduction.cpp" target="_top"><code class="literal">introduction.cpp</code></a>
- and <a class="link" href="boost_contract/tutorial.html#boost_contract.tutorial.non_member_functions" title="Non-Member Functions">Non-Member
- Functions</a>):
- </p>
- <p>
- </p>
- <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">contract</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
- <span class="keyword">void</span> <span class="identifier">inc</span><span class="special">(</span><span class="keyword">int</span><span class="special">&</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span>
- <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">old_ptr</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">old_x</span> <span class="special">=</span> <span class="identifier">BOOST_CONTRACT_OLDOF</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span> <span class="comment">// Old value.</span>
- <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">check</span> <span class="identifier">c</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">function</span><span class="special">()</span>
- <span class="special">.</span><span class="identifier">precondition</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="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">max</span><span class="special">());</span> <span class="comment">// Line 17.</span>
- <span class="special">})</span>
- <span class="special">.</span><span class="identifier">postcondition</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="special">*</span><span class="identifier">old_x</span> <span class="special">+</span> <span class="number">1</span><span class="special">);</span> <span class="comment">// Line 20.</span>
- <span class="special">})</span>
- <span class="special">;</span>
- <span class="special">++</span><span class="identifier">x</span><span class="special">;</span> <span class="comment">// Function body.</span>
- <span class="special">}</span>
- </pre>
- <p>
- </p>
- <p>
- When the above function <code class="computeroutput"><span class="identifier">inc</span></code>
- is called, this library will:
- </p>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- First, execute the functor passed to <code class="computeroutput"><span class="special">.</span><span class="identifier">precondition</span><span class="special">(...)</span></code>
- that asserts <code class="computeroutput"><span class="identifier">inc</span></code> precondition.
- </li>
- <li class="listitem">
- Then, execute <code class="computeroutput"><span class="identifier">inc</span></code> body
- (i.e., all the code that follows the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">check</span> <span class="identifier">c</span> <span class="special">=</span> <span class="special">...</span></code> declaration).
- </li>
- <li class="listitem">
- Last, execute the functor passed to <code class="computeroutput"><span class="special">.</span><span class="identifier">postcondition</span><span class="special">(...)</span></code>
- that asserts <code class="computeroutput"><span class="identifier">inc</span></code> postcondition
- (unless <code class="computeroutput"><span class="identifier">inc</span></code> body threw
- an exception).
- </li>
- </ul></div>
- <p>
- For example, if there is a bug in the code calling <code class="computeroutput"><span class="identifier">inc</span></code>
- so that the function is called with <code class="computeroutput"><span class="identifier">x</span></code>
- equal to <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">max</span><span class="special">()</span></code> then the program will terminate with an error
- message similar to the following (and it will be evident that the bug is in
- the calling code):
- </p>
- <pre class="programlisting">precondition assertion "x < std::numeric_limits<int>::max()" failed: file "introduction.cpp", line 17
- </pre>
- <p>
- Instead, if there is a bug in the implementation of <code class="computeroutput"><span class="identifier">inc</span></code>
- so that <code class="computeroutput"><span class="identifier">x</span></code> is not incremented
- by <code class="computeroutput"><span class="number">1</span></code> after the execution of the
- function body then the program will terminate with an error message similar
- to the following (and it will be evident that the bug is in <code class="computeroutput"><span class="identifier">inc</span></code>
- body): <a href="#ftn.boost_contract.introduction.f0" class="footnote" name="boost_contract.introduction.f0"><sup class="footnote">[2]</sup></a>
- </p>
- <pre class="programlisting">postcondition assertion "x == *old_x + 1" failed: file "introduction.cpp", line 20
- </pre>
- <p>
- By default, when an assertion fails this library prints an error message such
- the ones above to the standard error <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span></code> and
- terminates the program calling <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">terminate</span></code>
- (this behaviour can be customized to take any user-specified action including
- throwing exceptions, see <a class="link" href="boost_contract/advanced.html#boost_contract.advanced.throw_on_failures__and__noexcept__" title="Throw on Failures (and noexcept)">Throw
- on Failures</a>). Note that the error messages printed by this library contain
- all the information necessary to easily and uniquely identify the point in
- the code at which contract assertions fail. <a href="#ftn.boost_contract.introduction.f1" class="footnote" name="boost_contract.introduction.f1"><sup class="footnote">[3]</sup></a>
- </p>
- <div class="note"><table border="0" summary="Note">
- <tr>
- <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../doc/src/images/note.png"></td>
- <th align="left">Note</th>
- </tr>
- <tr><td align="left" valign="top"><p>
- C++11 lambda functions are necessary to use this library without manually
- writing a significant amount of boiler-plate code to program functors that
- assert the contracts (see <a class="link" href="boost_contract/extras.html#boost_contract.extras.no_lambda_functions__no_c__11_" title="No Lambda Functions (No C++11)">No
- Lambda Functions</a>). That said, this library implementation does not
- use C++11 features and should work on most modern C++ compilers (see <a class="link" href="boost_contract/getting_started.html" title="Getting Started">Getting Started</a>).
- </p></td></tr>
- </table></div>
- <p>
- In addition to contracts for non-member functions as shown the in the example
- above, this library allows to program contracts for constructors, destructors,
- and member functions. These can check class invariants and can also <span class="emphasis"><em>subcontract</em></span>
- inheriting and extending contracts from base classes (see <a href="../../example/features/introduction_public.cpp" target="_top"><code class="literal">introduction_public.cpp</code></a>
- and <a class="link" href="boost_contract/tutorial.html#boost_contract.tutorial.public_function_overrides__subcontracting_" title="Public Function Overrides (Subcontracting)">Public
- Function Overrides</a>): <a href="#ftn.boost_contract.introduction.f2" class="footnote" name="boost_contract.introduction.f2"><sup class="footnote">[4]</sup></a>
- </p>
- <p>
- </p>
- <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
- <span class="keyword">class</span> <span class="identifier">vector</span>
- <span class="preprocessor">#define</span> <span class="identifier">BASES</span> <span class="keyword">public</span> <span class="identifier">pushable</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span>
- <span class="special">:</span> <span class="identifier">BASES</span>
- <span class="special">{</span>
- <span class="keyword">public</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="comment">// For subcontracting.</span>
- <span class="preprocessor">#undef</span> <span class="identifier">BASES</span>
- <span class="keyword">void</span> <span class="identifier">invariant</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span> <span class="comment">// Checked in AND with base class invariants.</span>
- <span class="identifier">BOOST_CONTRACT_ASSERT</span><span class="special">(</span><span class="identifier">size</span><span class="special">()</span> <span class="special"><=</span> <span class="identifier">capacity</span><span class="special">());</span>
- <span class="special">}</span>
- <span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">push_back</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">value</span><span class="special">,</span>
- <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">virtual_</span><span class="special">*</span> <span class="identifier">v</span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span> <span class="comment">/* override */</span> <span class="special">{</span> <span class="comment">// For virtuals.</span>
- <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">old_ptr</span><span class="special"><</span><span class="keyword">unsigned</span><span class="special">></span> <span class="identifier">old_size</span> <span class="special">=</span>
- <span class="identifier">BOOST_CONTRACT_OLDOF</span><span class="special">(</span><span class="identifier">v</span><span class="special">,</span> <span class="identifier">size</span><span class="special">());</span> <span class="comment">// Old values for virtuals.</span>
- <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">check</span> <span class="identifier">c</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">public_function</span><span class="special"><</span> <span class="comment">// For overrides.</span>
- <span class="identifier">override_push_back</span><span class="special">>(</span><span class="identifier">v</span><span class="special">,</span> <span class="special">&</span><span class="identifier">vector</span><span class="special">::</span><span class="identifier">push_back</span><span class="special">,</span> <span class="keyword">this</span><span class="special">,</span> <span class="identifier">value</span><span class="special">)</span>
- <span class="special">.</span><span class="identifier">precondition</span><span class="special">([&]</span> <span class="special">{</span> <span class="comment">// Checked in OR with base preconditions.</span>
- <span class="identifier">BOOST_CONTRACT_ASSERT</span><span class="special">(</span><span class="identifier">size</span><span class="special">()</span> <span class="special"><</span> <span class="identifier">max_size</span><span class="special">());</span>
- <span class="special">})</span>
- <span class="special">.</span><span class="identifier">postcondition</span><span class="special">([&]</span> <span class="special">{</span> <span class="comment">// Checked in AND with base postconditions.</span>
- <span class="identifier">BOOST_CONTRACT_ASSERT</span><span class="special">(</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="special">*</span><span class="identifier">old_size</span> <span class="special">+</span> <span class="number">1</span><span class="special">);</span>
- <span class="special">})</span>
- <span class="special">;</span>
- <span class="identifier">vect_</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">value</span><span class="special">);</span>
- <span class="special">}</span>
- <span class="identifier">BOOST_CONTRACT_OVERRIDE</span><span class="special">(</span><span class="identifier">push_back</span><span class="special">)</span> <span class="comment">// Define `override_push_back` above.</span>
- <span class="comment">// Could program contracts for those as well.</span>
- <span class="keyword">unsigned</span> <span class="identifier">size</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">vect_</span><span class="special">.</span><span class="identifier">size</span><span class="special">();</span> <span class="special">}</span>
- <span class="keyword">unsigned</span> <span class="identifier">max_size</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">vect_</span><span class="special">.</span><span class="identifier">max_size</span><span class="special">();</span> <span class="special">}</span>
- <span class="keyword">unsigned</span> <span class="identifier">capacity</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">vect_</span><span class="special">.</span><span class="identifier">capacity</span><span class="special">();</span> <span class="special">}</span>
- <span class="keyword">private</span><span class="special">:</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">vect_</span><span class="special">;</span>
- <span class="special">};</span>
- </pre>
- <p>
- </p>
- <h4>
- <a name="boost_contract.introduction.h0"></a>
- <span class="phrase"><a name="boost_contract.introduction.language_support"></a></span><a class="link" href="index.html#boost_contract.introduction.language_support">Language
- Support</a>
- </h4>
- <p>
- The authors of this library advocate for contracts to be added to the core
- language. Adding contract programming to the C++ standard has a number of advantages
- over any library implementation (shorter and more concise syntax to program
- contracts, specify contracts in declarations instead of definitions, enforce
- contract constant-correctness, expected faster compile- and run-time, vendors
- could develop static analysis tools to recognize and check contracts statically
- when possible, compiler optimizations could be improved based on contract conditions,
- etc.).
- </p>
- <p>
- The <a class="link" href="boost_contract/bibliography.html#P0380_anchor">[P0380]</a> proposal supports basic contract
- programming, it was accepted and it will be included in C++20. This is undoubtedly
- a step in the right direction, but unfortunately <a class="link" href="boost_contract/bibliography.html#P0380_anchor">[P0380]</a>
- only supports pre- and postconditions while missing important features such
- as class invariants and old values in postconditions, not to mention the lack
- of more advanced features like subcontracting (more complete proposals like
- <a class="link" href="boost_contract/bibliography.html#N1962_anchor">[N1962]</a> were rejected by the C++ standard
- committee). All contracting programming features are instead supported by this
- library (see <a class="link" href="boost_contract/contract_programming_overview.html#boost_contract.contract_programming_overview.feature_summary" title="Feature Summary">Feature
- Summary</a> for a detailed comparison between the features supported by
- this library and the ones listed in different contract programming proposals,
- see <a class="link" href="boost_contract/bibliography.html" title="Bibliography">Bibliography</a> for a list
- of references considered during the design and implementation of this library,
- including the vast majority of contract programming proposals submitted to
- the C++ standard committee).
- </p>
- </div>
- <div class="footnotes">
- <br><hr style="width:100; text-align:left;margin-left: 0">
- <div id="ftn.boost_contract.f0" class="footnote"><p><a href="#boost_contract.f0" class="para"><sup class="para">[1] </sup></a>
- Design by Contract (DbC) is a registered trademark of the Eiffel Software company
- and it was first introduced by the Eiffel programming language (see <a class="link" href="boost_contract/bibliography.html#Meyer97_anchor">[Meyer97]</a>).
- </p></div>
- <div id="ftn.boost_contract.introduction.f0" class="footnote"><p><a href="#boost_contract.introduction.f0" class="para"><sup class="para">[2] </sup></a>
- In this example the function body is composed of a single trivial instruction
- <code class="computeroutput"><span class="special">++</span><span class="identifier">x</span></code>
- so it easy to check by visual inspection that it does not contain any bug
- and it will always increment <code class="computeroutput"><span class="identifier">x</span></code>
- by <code class="computeroutput"><span class="number">1</span></code> thus the function postcondition
- will never fail. In real production code, function bodies are rarely this
- simple and can hide bugs which make checking postconditions useful.
- </p></div>
- <div id="ftn.boost_contract.introduction.f1" class="footnote"><p><a href="#boost_contract.introduction.f1" class="para"><sup class="para">[3] </sup></a>
- <span class="bold"><strong>Rationale:</strong></span> The assertion failure message
- printed by this library follows a format similar to the message printed by
- Clang when the C-style <code class="computeroutput"><span class="identifier">assert</span></code>
- macro fails.
- </p></div>
- <div id="ftn.boost_contract.introduction.f2" class="footnote"><p><a href="#boost_contract.introduction.f2" class="para"><sup class="para">[4] </sup></a>
- The <code class="computeroutput"><span class="identifier">pushable</span></code> base class is
- used in this example just to show subcontracting, it is somewhat arbitrary
- and it will likely not appear in real production code.
- </p></div>
- </div>
- </div>
- <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
- <td align="left"><p><small>Last revised: December 10, 2019 at 00:23:48 GMT</small></p></td>
- <td align="right"><div class="copyright-footer"></div></td>
- </tr></table>
- <hr>
- <div class="spirit-nav"><a accesskey="n" href="boost_contract/full_table_of_contents.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a></div>
- </body>
- </html>
|