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value_or_error.html

value_or_error.html 4.8 KB
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  3. <title>value_or_error&lt;T, U&gt; - Boost.Outcome documentation</title>
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  13.   <div class="titlepage"><div><div><h1 style="clear: both"><code>value_or_error&lt;T, U&gt;</code></h1></div></div></div>
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  14.   <p>A customisable converter of <a href="../../reference/concepts/valueorerror.html" class="api-reference"><code>ValueOrError&lt;T, E&gt;</code></a>
    15. 

  15.  concept matching types. It must have the following form:</p>
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  16. <div class="highlight"><pre class="chroma"><code class="language-c++" data-lang="c++"><span class="c1">// `T` will be the destination basic_result or basic_outcome.
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  17. </span><span class="c1">// `U` will be the decayed form of the `ValueOrError&lt;T, E&gt;` concept matching input type.
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  18. </span><span class="c1"></span><span class="k">template</span> <span class="o">&lt;</span><span class="k">class</span><span class="err"> </span><span class="nc">T</span><span class="o">&gt;</span> <span class="k">struct</span> <span class="n">value_or_error</span><span class="o">&lt;</span><span class="n">T</span><span class="p">,</span> <span class="n">U</span><span class="o">&gt;</span>
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  19. <span class="p">{</span>
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  20.   <span class="c1">// False to indicate that this converter wants `basic_result`/`basic_outcome` to reject all other `basic_result`
    21. 

  21. </span><span class="c1"></span>  <span class="k">static</span> <span class="k">constexpr</span> <span class="kt">bool</span> <span class="n">enable_result_inputs</span> <span class="o">=</span> <span class="nb">false</span><span class="p">;</span>
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  22.   <span class="c1">// False to indicate that this converter wants `basic_outcome` to reject all other `basic_outcome`
    23. 

  23. </span><span class="c1"></span>  <span class="k">static</span> <span class="k">constexpr</span> <span class="kt">bool</span> <span class="n">enable_outcome_inputs</span> <span class="o">=</span> <span class="nb">false</span><span class="p">;</span>
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  24.   
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  25.   <span class="c1">// `X` will be the raw input form of `U`. It must return a `T`.
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  26. </span><span class="c1"></span>  <span class="k">template</span><span class="o">&lt;</span><span class="k">class</span><span class="err"> </span><span class="nc">X</span><span class="o">&gt;</span> <span class="k">constexpr</span> <span class="n">T</span> <span class="k">operator</span><span class="p">()(</span><span class="n">X</span> <span class="o">&amp;&amp;</span><span class="n">v</span><span class="p">);</span>
    27. 

  27. <span class="p">};</span>
    28. 

  28. </code></pre></div>
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  29. <p><em>Overridable</em>: By template specialisation into the <code>convert</code> namespace.</p>
    30. 

  30. 

  31. <p><em>Default</em>: If decayed <code>X</code> is same as <code>U</code>, concept <code>ValueOrError&lt;U&gt;</code> matches, <code>X::value_type</code> is <code>void</code> or is explicitly constructible to <code>T::value_type</code>, and <code>X::error_type</code> is <code>void</code> or is explicitly constructible to <code>T::error_type</code>, then <code>operator()(X &amp;&amp;)</code> is made available.</p>
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  32. 

  33. <p><code>operator()(X &amp;&amp;v)</code> tests if <code>v.has_value()</code> is true, if so then a <code>T</code> with successful value is returned, else a <code>T</code> with unsuccessful value. If the input type was <code>void</code>, a default constructed value is used for either, else a move/copy construction from the source is performed.</p>
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  34. 

  35. <p><em>Namespace</em>: <code>BOOST_OUTCOME_V2_NAMESPACE::convert</code></p>
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  36. 

  37. <p><em>Header</em>: <code>&lt;boost/outcome/convert.hpp&gt;</code></p>
    38. 

  38. 

  39. 

  40.         </div><p><small>Last revised: December 15, 2018 at 17:49:37 UTC</small></p>
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