1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html><meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 3<title>The Application - Boost.Outcome documentation</title> 4<link rel="stylesheet" href="../../../css/boost.css" type="text/css"> 5<meta name="generator" content="Hugo 0.52 with Boostdoc theme"> 6<meta name="viewport" content="width=device-width,initial-scale=1.0"/> 7 8<link rel="icon" href="../../../images/favicon.ico" type="image/ico"/> 9<body><div class="spirit-nav"> 10<a accesskey="p" href="../../../tutorial/advanced/interop/filelib.html"><img src="../../../images/prev.png" alt="Prev"></a> 11 <a accesskey="u" href="../../../tutorial/advanced/interop.html"><img src="../../../images/up.png" alt="Up"></a> 12 <a accesskey="h" href="../../../index.html"><img src="../../../images/home.png" alt="Home"></a><a accesskey="n" href="../../../tutorial/advanced/interop/app-map-httplib1.html"><img src="../../../images/next.png" alt="Next"></a></div><div id="content"> 13 <div class="titlepage"><div><div><h1 style="clear: both">The Application</h1></div></div></div> 14 <p>The application is of course also based on Outcome, and like the HTTP library 15is also of mixed-failure design in that failure can be returned via error code, 16type erased <code>exception_ptr</code> or indeed a C++ exception throw.</p> 17 18<div class="code-snippet"><div class="highlight"><pre class="chroma"><code class="language-c++" data-lang="c++"><span class="c1">// This is the namespace of the application which is connecting together the httplib, 19</span><span class="c1">// filelib and tidylib libraries into a solution. 20</span><span class="c1"></span><span class="k">namespace</span> <span class="n">app</span> 21<span class="p">{</span> 22 <span class="c1">// Create an ADL bridge so copy/move hooks will be searched for in this namespace 23</span><span class="c1"></span> <span class="k">struct</span> <span class="nl">error_code</span> <span class="p">:</span> <span class="k">public</span> <span class="n">std</span><span class="o">::</span><span class="n">error_code</span> 24 <span class="p">{</span> 25 <span class="c1">// passthrough 26</span><span class="c1"></span> <span class="k">using</span> <span class="n">std</span><span class="o">::</span><span class="n">error_code</span><span class="o">::</span><span class="n">error_code</span><span class="p">;</span> 27 <span class="n">error_code</span><span class="p">()</span> <span class="o">=</span> <span class="k">default</span><span class="p">;</span> 28 <span class="n">error_code</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">error_code</span> <span class="n">ec</span><span class="p">)</span> 29 <span class="o">:</span> <span class="n">std</span><span class="o">::</span><span class="n">error_code</span><span class="p">(</span><span class="n">ec</span><span class="p">)</span> 30 <span class="p">{</span> 31 <span class="p">}</span> 32 <span class="p">};</span> 33 <span class="c1">// Localise an outcome implementation for this namespace 34</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="o">></span> 35 <span class="k">using</span> <span class="n">outcome</span> <span class="o">=</span> <span class="c1">// 36</span><span class="c1"></span> <span class="n">BOOST_OUTCOME_V2_NAMESPACE</span><span class="o">::</span><span class="n">outcome</span><span class="o"><</span><span class="n">T</span><span class="p">,</span> <span class="n">error_code</span> <span class="cm">/*, std::exception_ptr */</span><span class="o">></span><span class="p">;</span> 37 <span class="k">using</span> <span class="n">BOOST_OUTCOME_V2_NAMESPACE</span><span class="o">::</span><span class="n">success</span><span class="p">;</span> 38<span class="p">}</span> <span class="c1">// namespace app 39</span><span class="c1"></span></code></pre></div><a href="https://github.com/boostorg/outcome/tree/master/doc/src/snippets/finale.cpp#L178" class="code-snippet-url" target="_blank">View this code on Github</a></div> 40 41 42<p>Here we localise a passthrough <code>error_code</code> solely for the purpose of ADL bridging, otherwise 43the localised <code>outcome</code> configured is the default one which comes with Outcome. 44<a href="../../../tutorial/advanced/hooks/adl_bridging.html">We covered this technique of “passthrough <code>error_code</code>” earlier in this tutorial</a>.</p> 45 46<p>The way we are going to configure interop is as follows:</p> 47 48<ol> 49<li>The application shall use <code>error_code</code> for anticipated failure and C++ 50exception throws for unanticipated failure.</li> 51<li>We shall choose the convention that <code>app::outcome</code> with exception ptr 52solely and exclusively represents a type erased failure from a third party 53library.</li> 54</ol> 55 56<p>Thus if one calls <code>.value()</code> on an <code>app::outcome</code>, both anticipated failure 57within the app and type erased failure from a third party library shall be 58converted to a C++ exception throw.</p> 59 60 61 </div><p><small>Last revised: February 11, 2019 at 17:14:51 UTC</small></p> 62<hr> 63<div class="spirit-nav"> 64<a accesskey="p" href="../../../tutorial/advanced/interop/filelib.html"><img src="../../../images/prev.png" alt="Prev"></a> 65 <a accesskey="u" href="../../../tutorial/advanced/interop.html"><img src="../../../images/up.png" alt="Up"></a> 66 <a accesskey="h" href="../../../index.html"><img src="../../../images/home.png" alt="Home"></a><a accesskey="n" href="../../../tutorial/advanced/interop/app-map-httplib1.html"><img src="../../../images/next.png" alt="Next"></a></div></body> 67</html> 68
