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56 lines
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<div class="titlepage"><div><div><h1 style="clear: both">ADL bridging</h1></div></div></div>
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<p>In a previous section, we used the <code>failure_info</code> type to create
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the ADL bridge into the namespace where the ADL discovered <a href="../../../reference/functions/policy.html"><code>outcome_throw_as_system_error_with_payload()</code></a> function was to be found.</p>
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<p>Here we do the same, but more directly by creating a thin clone of <code>std::error_code</code>
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into the local namespace. This ensures that this namespace will be searched by the
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compiler when discovering the event hooks.</p>
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<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>
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<span class="p">{</span>
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<span class="c1">// Use the error_code type as the ADL bridge for the hooks by creating a type here
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</span><span class="c1"></span> <span class="c1">// It can be any type that your localised result uses, including the value type but
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</span><span class="c1"></span> <span class="c1">// by localising the error code type here you prevent nasty surprises later when the
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</span><span class="c1"></span> <span class="c1">// value type you use doesn't trigger the ADL bridge.
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</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>
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<span class="p">{</span>
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<span class="c1">// literally passthrough
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</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>
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<span class="n">error_code</span><span class="p">()</span> <span class="o">=</span> <span class="k">default</span><span class="p">;</span>
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<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>
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<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>
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<span class="p">{</span>
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<span class="p">}</span>
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<span class="p">};</span>
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<span class="c1">// Localise result and outcome to using the local error_code so this namespace gets looked up for the hooks
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</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">R</span><span class="o">></span> <span class="k">using</span> <span class="n">result</span> <span class="o">=</span> <span class="n">BOOST_OUTCOME_V2_NAMESPACE</span><span class="o">::</span><span class="n">result</span><span class="o"><</span><span class="n">R</span><span class="p">,</span> <span class="n">error_code</span><span class="o">></span><span class="p">;</span>
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<span class="k">template</span> <span class="o"><</span><span class="k">class</span><span class="err"> </span><span class="nc">R</span><span class="o">></span> <span class="k">using</span> <span class="n">outcome</span> <span class="o">=</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">R</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>
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<span class="p">}</span>
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</code></pre></div><a href="https://github.com/boostorg/outcome/tree/master/doc/src/snippets/error_code_extended.cpp#L95" class="code-snippet-url" target="_blank">View this code on Github</a></div>
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<p>For convenience, we template alias local copies of <code>result</code> and <code>outcome</code> in this
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namespace bound to the ADL bridging <code>error_code</code>.</p>
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</div><p><small>Last revised: February 08, 2019 at 22:18:08 UTC</small></p>
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