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
/
advanced
/
payload
/
copy_file2.html

copy_file2.html 6.1 KB
History Raw

1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162 
  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>Upgrading the Filesystem TS - 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/advanced/payload/copy_file.html"><img src="../../../images/prev.png" alt="Prev"></a>
    11. 

  11.     <a accesskey="u" href="../../../tutorial/advanced/payload.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/advanced/payload/copy_file3.html"><img src="../../../images/next.png" alt="Next"></a></div><div id="content">
    13. 

  13.   <div class="titlepage"><div><div><h1 style="clear: both">Upgrading the Filesystem TS</h1></div></div></div>
    14. 

  14.   <p>An Outcome based solution to the dual overload problem is straightforward:</p>
    15. 

  15. 

  16. <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">filesystem2</span>
    17. 

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

  18.   <span class="c1">// Error code + paths related to a failure. Also causes ADL discovery to check this namespace.
    19. 

  19. </span><span class="c1"></span>  <span class="k">struct</span> <span class="n">failure_info</span>
    20. 

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

  21.     <span class="n">std</span><span class="o">::</span><span class="n">error_code</span> <span class="n">ec</span><span class="p">;</span>
    22. 

  22.     <span class="n">path</span> <span class="n">path1</span><span class="p">,</span> <span class="n">path2</span><span class="p">;</span>
    23. 

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

  24. 

  25.   <span class="c1">// Tell Outcome that failure_info is to be treated as a std::error_code
    26. 

  26. </span><span class="c1"></span>  <span class="kr">inline</span> <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">error_code</span> <span class="o">&amp;</span><span class="n">make_error_code</span><span class="p">(</span><span class="k">const</span> <span class="n">failure_info</span> <span class="o">&amp;</span><span class="n">fi</span><span class="p">)</span> <span class="p">{</span> <span class="k">return</span> <span class="n">fi</span><span class="p">.</span><span class="n">ec</span><span class="p">;</span> <span class="p">}</span>
    27. 

  27. 

  28.   <span class="c1">// Localise an outcome implementation specific to this namespace. Normally would just
    29. 

  29. </span><span class="c1"></span>  <span class="c1">// be `result`, but for clarity we&#39;ll use `fs_result`.
    30. 

  30. </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">using</span> <span class="n">fs_result</span> <span class="o">=</span> <span class="n">outcome</span><span class="o">::</span><span class="n">result</span><span class="o">&lt;</span><span class="n">T</span><span class="p">,</span> <span class="n">failure_info</span><span class="o">&gt;</span><span class="p">;</span>
    31. 

  31. 

  32.   <span class="cm">/*! Copies the file at path `from` to path `to`.
    33. 

  33. </span><span class="cm">  \returns Successful if file was successfully copied, otherwise the error code reported
    34. 

  34. </span><span class="cm">  by the operating system plus a payload of the paths involved.
    35. 

  35. </span><span class="cm">  \throws Never throws.
    36. 

  36. </span><span class="cm">  */</span>
    37. 

  37.   <span class="n">fs_result</span><span class="o">&lt;</span><span class="kt">void</span><span class="o">&gt;</span> <span class="n">copy_file</span><span class="p">(</span><span class="k">const</span> <span class="n">path</span> <span class="o">&amp;</span><span class="n">from</span><span class="p">,</span> <span class="k">const</span> <span class="n">path</span> <span class="o">&amp;</span><span class="n">to</span><span class="p">)</span> <span class="k">noexcept</span><span class="p">;</span>
    38. 

  38. <span class="p">}</span>
    39. 

  39. </code></pre></div><a href="https://github.com/boostorg/outcome/tree/master/doc/src/snippets/outcome_payload.cpp#L69" class="code-snippet-url" target="_blank">View this code on Github</a></div>
    40. 

  40. 

  41. 

  42. <p>Starting at the bottom, there is now a single <code>copy_file()</code> function which returns a <code>fs_result&lt;void&gt;</code>.
    43. 

  43. As <code>result</code> is either successful or not, there is no longer any point in returning a boolean, so we
    44. 

  44. simply return <code>void</code> on success. On failure, as the template alias <code>fs_result&lt;T&gt;</code> above it shows,
    45. 

  45. we are returning a <code>failure_info</code> structure containing an error code and the same additional information
    46. 

  46. as <code>filesystem_error</code> provides.</p>
    47. 

  47. 

  48. <p>It is important to note that the fact that <code>failure_info</code> is defined in namespace <code>filesystem2</code> is very
    49. 

  49. important. This is because Outcome uses <a href="http://en.cppreference.com/w/cpp/language/adl">Argument Dependent Lookup (ADL)</a>
    50. 

  50. to find the <code>make_error_code()</code>
    51. 

  51. function, as well as other customisation point free functions. In other words, only the namespaces as
    52. 

  52. defined by ADL are searched when finding a free function telling us what to do for <code>failure_info</code>,
    53. 

  53. which includes the namespace <code>failure_info</code> is declared into.</p>
    54. 

  54. 

  55. 

  56.         </div><p><small>Last revised: February 08, 2019 at 22:18:08 UTC</small></p>
    57. 

  57. <hr>
    58. 

  58. <div class="spirit-nav">
    59. 

  59. <a accesskey="p" href="../../../tutorial/advanced/payload/copy_file.html"><img src="../../../images/prev.png" alt="Prev"></a>
    60. 

  60.     <a accesskey="u" href="../../../tutorial/advanced/payload.html"><img src="../../../images/up.png" alt="Up"></a>
    61. 

  61.     <a accesskey="h" href="../../../index.html"><img src="../../../images/home.png" alt="Home"></a><a accesskey="n" href="../../../tutorial/advanced/payload/copy_file3.html"><img src="../../../images/next.png" alt="Next"></a></div></body>
    62. 

  62. </html>
    63.