Home Explore Help
Register Sign In
devn00b
/
EQ2EMu
9
3
Fork 0
Files Issues 59
Tree: ff02b05cfd
Branches Tags
EQ2EMu
/
EQ2
/
source
/
depends
/
boost_1_72_0
/
libs
/
outcome
/
doc
/
html
/
tutorial
/
essential
/
no-value
/
custom.html

custom.html 7.1 KB
History Raw

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960 
  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    2. 

  2. <html><meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    3. 

  3. <title>A custom no-value policy - Boost.Outcome documentation</title>
    4. 

  4. <link rel="stylesheet" href="../../../css/boost.css" type="text/css">
    5. 

  5. <meta name="generator" content="Hugo 0.52 with Boostdoc theme">
    6. 

  6. <meta name="viewport" content="width=device-width,initial-scale=1.0"/>
    7. 

  7. 

  8. <link rel="icon" href="../../../images/favicon.ico" type="image/ico"/>
    9. 

  9. <body><div class="spirit-nav">
    10. 

  10. <a accesskey="p" href="../../../tutorial/essential/no-value.html"><img src="../../../images/prev.png" alt="Prev"></a>
    11. 

  11.     <a accesskey="u" href="../../../tutorial/essential/no-value.html"><img src="../../../images/up.png" alt="Up"></a>
    12. 

  12.     <a accesskey="h" href="../../../index.html"><img src="../../../images/home.png" alt="Home"></a><a accesskey="n" href="../../../tutorial/essential/no-value/builtin.html"><img src="../../../images/next.png" alt="Next"></a></div><div id="content">
    13. 

  13.   <div class="titlepage"><div><div><h1 style="clear: both">A custom no-value policy</h1></div></div></div>
    14. 

  14.   <p>If you want your <code>basic_outcome&lt;&gt;</code> or <code>basic_result&lt;&gt;</code> instances to call
    15. 

  15. <code>std::abort()</code> whenever <code>.value()</code> is called on an object that does not contain a value, or <code>.error()</code> is called on an object that does not contain an error, you will need to define your own no-value policy as follows:</p>
    16. 

  16. 

  17. <div class="code-snippet"><div class="highlight"><pre class="chroma"><code class="language-c++" data-lang="c++"><span class="k">struct</span> <span class="nl">abort_policy</span> <span class="p">:</span> <span class="n">outcome</span><span class="o">::</span><span class="n">policy</span><span class="o">::</span><span class="n">base</span>
    18. 

  18. <span class="p">{</span>
    19. 

  19.   <span class="k">template</span> <span class="o">&lt;</span><span class="k">class</span><span class="err"> </span><span class="nc">Impl</span><span class="o">&gt;</span> <span class="k">static</span> <span class="k">constexpr</span> <span class="kt">void</span> <span class="n">wide_value_check</span><span class="p">(</span><span class="n">Impl</span> <span class="o">&amp;&amp;</span><span class="n">self</span><span class="p">)</span>
    20. 

  20.   <span class="p">{</span>
    21. 

  21.     <span class="k">if</span><span class="p">(</span><span class="o">!</span><span class="n">base</span><span class="o">::</span><span class="n">_has_value</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">forward</span><span class="o">&lt;</span><span class="n">Impl</span><span class="o">&gt;</span><span class="p">(</span><span class="n">self</span><span class="p">)))</span>
    22. 

  22.       <span class="n">std</span><span class="o">::</span><span class="n">abort</span><span class="p">();</span>
    23. 

  23.   <span class="p">}</span>
    24. 

  24. 

  25.   <span class="k">template</span> <span class="o">&lt;</span><span class="k">class</span><span class="err"> </span><span class="nc">Impl</span><span class="o">&gt;</span> <span class="k">static</span> <span class="k">constexpr</span> <span class="kt">void</span> <span class="n">wide_error_check</span><span class="p">(</span><span class="n">Impl</span> <span class="o">&amp;&amp;</span><span class="n">self</span><span class="p">)</span>
    26. 

  26.   <span class="p">{</span>
    27. 

  27.     <span class="k">if</span><span class="p">(</span><span class="o">!</span><span class="n">base</span><span class="o">::</span><span class="n">_has_error</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">forward</span><span class="o">&lt;</span><span class="n">Impl</span><span class="o">&gt;</span><span class="p">(</span><span class="n">self</span><span class="p">)))</span>
    28. 

  28.       <span class="n">std</span><span class="o">::</span><span class="n">abort</span><span class="p">();</span>
    29. 

  29.   <span class="p">}</span>
    30. 

  30. 

  31.   <span class="k">template</span> <span class="o">&lt;</span><span class="k">class</span><span class="err"> </span><span class="nc">Impl</span><span class="o">&gt;</span> <span class="k">static</span> <span class="k">constexpr</span> <span class="kt">void</span> <span class="n">wide_exception_check</span><span class="p">(</span><span class="n">Impl</span> <span class="o">&amp;&amp;</span><span class="n">self</span><span class="p">)</span>
    32. 

  32.   <span class="p">{</span>
    33. 

  33.     <span class="k">if</span><span class="p">(</span><span class="o">!</span><span class="n">base</span><span class="o">::</span><span class="n">_has_exception</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">forward</span><span class="o">&lt;</span><span class="n">Impl</span><span class="o">&gt;</span><span class="p">(</span><span class="n">self</span><span class="p">)))</span>
    34. 

  34.       <span class="n">std</span><span class="o">::</span><span class="n">abort</span><span class="p">();</span>
    35. 

  35.   <span class="p">}</span>
    36. 

  36. <span class="p">};</span>
    37. 

  37. </code></pre></div><a href="https://github.com/boostorg/outcome/tree/master/doc/src/snippets/policies.cpp#L36" class="code-snippet-url" target="_blank">View this code on Github</a></div>
    38. 

  38. 

  39. 

  40. <p>All policies ought to inherit from <a href="../../../reference/policies/base.html" class="api-reference"><code>base</code></a>
    41. 

  41.  in order to provide your policy implementation with
    42. 

  42. the internal policy API for accessing and manipulating <code>result</code> and <code>outcome</code> state.</p>
    43. 

  43. 

  44. <p>Once the policy is defined, you have to specify it when providing your own
    45. 

  45. <code>basic_outcome</code> specialization:</p>
    46. 

  46. 

  47. <div class="code-snippet"><div class="highlight"><pre class="chroma"><code class="language-c++" data-lang="c++"><span class="k">template</span> <span class="o">&lt;</span><span class="k">typename</span> <span class="n">T</span><span class="o">&gt;</span>
    48. 

  48. <span class="k">using</span> <span class="n">strictOutcome</span> <span class="o">=</span>  <span class="c1">//
    49. 

  49. </span><span class="c1"></span><span class="n">outcome</span><span class="o">::</span><span class="n">basic_outcome</span><span class="o">&lt;</span><span class="n">T</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">error_code</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">exception_ptr</span><span class="p">,</span> <span class="n">abort_policy</span><span class="o">&gt;</span><span class="p">;</span>
    50. 

  50. </code></pre></div><a href="https://github.com/boostorg/outcome/tree/master/doc/src/snippets/policies.cpp#L94" class="code-snippet-url" target="_blank">View this code on Github</a></div>
    51. 

  51. 

  52. 

  53. 

  54.         </div><p><small>Last revised: February 08, 2019 at 22:18:08 UTC</small></p>
    55. 

  55. <hr>
    56. 

  56. <div class="spirit-nav">
    57. 

  57. <a accesskey="p" href="../../../tutorial/essential/no-value.html"><img src="../../../images/prev.png" alt="Prev"></a>
    58. 

  58.     <a accesskey="u" href="../../../tutorial/essential/no-value.html"><img src="../../../images/up.png" alt="Up"></a>
    59. 

  59.     <a accesskey="h" href="../../../index.html"><img src="../../../images/home.png" alt="Home"></a><a accesskey="n" href="../../../tutorial/essential/no-value/builtin.html"><img src="../../../images/next.png" alt="Next"></a></div></body>
    60. 

  60. </html>
    61.