mirror of
https://github.com/boostorg/outcome.git
synced 2026-02-18 14:22:08 +00:00
82 lines
7.1 KiB
HTML
82 lines
7.1 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html><meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<title>Hook result - Boost.Outcome documentation</title>
|
|
<link rel="stylesheet" href="../../css/boost.css" type="text/css">
|
|
<meta name="generator" content="Hugo 0.52 with Boostdoc theme">
|
|
<meta name="viewport" content="width=device-width,initial-scale=1.0"/>
|
|
|
|
<link rel="icon" href="../../images/favicon.ico" type="image/ico"/>
|
|
<body><div id="boost-common-heading-doc" style="background: #574D74 url('../../images/header-bg.png') repeat-x top left;">
|
|
<div class="heading-inner" style="background: url('../../images/header-fg.png') no-repeat top left;">
|
|
<div class="heading-placard"></div>
|
|
|
|
<h1 class="heading-title">
|
|
<a href="../../">
|
|
<img src="../../images/space.png" alt="Boost C++ Libraries" class="heading-logo" />
|
|
<span class="heading-boost">Boost</span>
|
|
<span class="heading-cpplibraries">C++ Libraries</span>
|
|
</a>
|
|
</h1>
|
|
|
|
<p class="heading-quote">
|
|
<q>...one of the most highly
|
|
regarded and expertly designed C++ library projects in the
|
|
world.</q> <span class="heading-attribution">— <a href=
|
|
"http://www.gotw.ca/" class="external">Herb Sutter</a> and <a href=
|
|
"http://en.wikipedia.org/wiki/Andrei_Alexandrescu" class="external">Andrei
|
|
Alexandrescu</a>, <a href=
|
|
"http://safari.awprofessional.com/?XmlId=0321113586" class="external">C++
|
|
Coding Standards</a></span></p>
|
|
</div>
|
|
</div>
|
|
<div id="boost-common-heading-doc-spacer"></div>
|
|
<div class="spirit-nav">
|
|
<a accesskey="p" href="../../tutorial/hooks/adl_bridging.html"><img src="../../images/prev.png" alt="Prev"></a>
|
|
<a accesskey="u" href="../../tutorial/hooks.html"><img src="../../images/up.png" alt="Up"></a>
|
|
<a accesskey="h" href="../../index.html"><img src="../../images/home.png" alt="Home"></a><a accesskey="n" href="../../tutorial/hooks/poke_exception.html"><img src="../../images/next.png" alt="Next"></a></div><div id="content">
|
|
<div class="titlepage"><div><div><h2 class="title" style="clear: both">Hook result</h2></div></div></div>
|
|
<p>We now tell Outcome that for every instance of our localised <code>result<T></code>, that
|
|
on failure construction only, we want custom code to be run which increments the current
|
|
slot in TLS storage and writes the current stack backtrace into it.</p>
|
|
|
|
<div class="code-snippet"><div class="highlight"><pre class="chroma"><code class="language-c++" data-lang="c++"><span class="k">namespace</span> <span class="n">error_code_extended</span>
|
|
<span class="p">{</span>
|
|
<span class="c1">// Specialise the result construction hook for our localised result
|
|
</span><span class="c1"></span> <span class="c1">// We hook any non-copy, non-move, non-inplace construction, capturing a stack backtrace
|
|
</span><span class="c1"></span> <span class="c1">// if the result is errored.
|
|
</span><span class="c1"></span> <span class="k">template</span> <span class="o"><</span><span class="k">class</span><span class="err"> </span><span class="nc">T</span><span class="p">,</span> <span class="k">class</span><span class="err"> </span><span class="nc">U</span><span class="o">></span> <span class="kr">inline</span> <span class="kt">void</span> <span class="n">hook_result_construction</span><span class="p">(</span><span class="n">result</span><span class="o"><</span><span class="n">T</span><span class="o">></span> <span class="o">*</span><span class="n">res</span><span class="p">,</span> <span class="n">U</span> <span class="o">&&</span> <span class="cm">/*unused*/</span><span class="p">)</span> <span class="k">noexcept</span>
|
|
<span class="p">{</span>
|
|
<span class="k">if</span><span class="p">(</span><span class="n">res</span><span class="o">-></span><span class="n">has_error</span><span class="p">())</span>
|
|
<span class="p">{</span>
|
|
<span class="c1">// Grab the next extended info slot in the TLS
|
|
</span><span class="c1"></span> <span class="n">extended_error_info</span> <span class="o">&</span><span class="n">eei</span> <span class="o">=</span> <span class="n">mythreadlocaldata</span><span class="p">().</span><span class="n">next</span><span class="p">();</span>
|
|
|
|
<span class="c1">// Write the index just grabbed into the spare uint16_t
|
|
</span><span class="c1"></span> <span class="n">BOOST_OUTCOME_V2_NAMESPACE</span><span class="o">::</span><span class="n">hooks</span><span class="o">::</span><span class="n">set_spare_storage</span><span class="p">(</span><span class="n">res</span><span class="p">,</span> <span class="n">mythreadlocaldata</span><span class="p">().</span><span class="n">current</span> <span class="o">-</span> <span class="mi">1</span><span class="p">);</span>
|
|
|
|
<span class="c1">// Capture a backtrace into my claimed extended info slot in the TLS
|
|
</span><span class="c1"></span> <span class="n">eei</span><span class="p">.</span><span class="n">items</span> <span class="o">=</span> <span class="o">::</span><span class="n">backtrace</span><span class="p">(</span><span class="n">eei</span><span class="p">.</span><span class="n">backtrace</span><span class="p">.</span><span class="n">data</span><span class="p">(),</span> <span class="n">eei</span><span class="p">.</span><span class="n">backtrace</span><span class="p">.</span><span class="n">size</span><span class="p">());</span>
|
|
<span class="p">}</span>
|
|
<span class="p">}</span>
|
|
<span class="p">}</span>
|
|
</code></pre></div><a href="https://github.com/ned14/boost-outcome/tree/master/doc/src/snippets/error_code_extended.cpp#L119" class="code-snippet-url" target="_blank">View this code on Github</a></div>
|
|
|
|
|
|
<p>The only non-obvious part above is the call to <a href="reference/result/#standardese-outcome_v2_xxx__hooks__set_spare_storage-R-S-NoValuePolicy--result_or_outcome-R-S-NoValuePolicy---uint16_t-" class="api-reference"><i class="fa fa-book" aria-hidden="true"></i> hooks::set_spare_storage()</a>
|
|
.
|
|
Both <code>result</code> and <code>outcome</code> keep their internal state metadata in a <code>uint32_t</code>,
|
|
half of which is not used by Outcome. As it can be very useful to keep a small
|
|
unique number attached to any particular <code>result</code> or <code>outcome</code> instance, we
|
|
permit user code to set those sixteen bits to anything they feel like.
|
|
The corresponding function to retrieve those sixteen bits is <a href="reference/result/#standardese-outcome_v2_xxx__hooks__spare_storage-R-S-NoValuePolicy--result_or_outcome-R-S-NoValuePolicy-const--" class="api-reference"><i class="fa fa-book" aria-hidden="true"></i> hooks::spare_storage()</a>
|
|
.</p>
|
|
|
|
|
|
</div><p><small>Last revised: December 05, 2018 at 14:18:52 UTC</small></p>
|
|
<hr>
|
|
<div class="spirit-nav">
|
|
<a accesskey="p" href="../../tutorial/hooks/adl_bridging.html"><img src="../../images/prev.png" alt="Prev"></a>
|
|
<a accesskey="u" href="../../tutorial/hooks.html"><img src="../../images/up.png" alt="Up"></a>
|
|
<a accesskey="h" href="../../index.html"><img src="../../images/home.png" alt="Home"></a><a accesskey="n" href="../../tutorial/hooks/poke_exception.html"><img src="../../images/next.png" alt="Next"></a></div></body>
|
|
</html>
|