assert-relation.html 7.5 KB

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  7. <title>The MPL Reference Manual: BOOST_MPL_ASSERT_RELATION</title>
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  12. <td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./macros.html" class="navigation-link">Macros</a> / <a href="./asserts.html" class="navigation-link">Asserts</a> / <a href="./assert-relation.html" class="navigation-link">BOOST_MPL_ASSERT_RELATION</a></td>
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  14. <div class="section" id="boost-mpl-assert-relation">
  15. <h1><a class="toc-backref" href="./asserts.html#id1591">BOOST_MPL_ASSERT_RELATION</a></h1>
  16. <div class="section" id="id1308">
  17. <h3><a class="subsection-title" href="#synopsis" name="synopsis">Synopsis</a></h3>
  18. <pre class="literal-block">
  19. #define <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( x, relation, y ) \
  20. <em>unspecified token sequence</em> \
  21. /**/
  22. </pre>
  23. </div>
  24. <div class="section" id="id1309">
  25. <h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
  26. <p>A specialized assertion macro for checking numerical conditions. Generates
  27. a compilation error when the condition <tt class="literal"><span class="pre">(</span> <span class="pre">x</span> <span class="pre">relation</span> <span class="pre">y</span> <span class="pre">)</span></tt>
  28. doesn't hold.</p>
  29. </div>
  30. <div class="section" id="id1310">
  31. <h3><a class="subsection-title" href="#header" name="header">Header</a></h3>
  32. <pre class="literal-block">
  33. #include &lt;<a href="../../../../boost/mpl/assert.hpp" class="header">boost/mpl/assert.hpp</a>&gt;
  34. </pre>
  35. </div>
  36. <div class="section" id="id1311">
  37. <h3><a class="subsection-title" href="#parameters" name="parameters">Parameters</a></h3>
  38. <table border="1" class="docutils table">
  39. <colgroup>
  40. <col width="15%" />
  41. <col width="36%" />
  42. <col width="48%" />
  43. </colgroup>
  44. <thead valign="bottom">
  45. <tr><th class="head">Parameter</th>
  46. <th class="head">Requirement</th>
  47. <th class="head">Description</th>
  48. </tr>
  49. </thead>
  50. <tbody valign="top">
  51. <tr><td><tt class="literal"><span class="pre">x</span></tt></td>
  52. <td>An integral constant</td>
  53. <td>Left operand of the checked relation.</td>
  54. </tr>
  55. <tr><td><tt class="literal"><span class="pre">y</span></tt></td>
  56. <td>An integral constant</td>
  57. <td>Right operand of the checked relation.</td>
  58. </tr>
  59. <tr><td><tt class="literal"><span class="pre">relation</span></tt></td>
  60. <td>A C++ operator token</td>
  61. <td>An operator token for the relation being
  62. checked.</td>
  63. </tr>
  64. </tbody>
  65. </table>
  66. </div>
  67. <div class="section" id="id1312">
  68. <h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
  69. <p>For any integral constants <tt class="literal"><span class="pre">x</span></tt>, <tt class="literal"><span class="pre">y</span></tt> and a legal C++ operator token <tt class="literal"><span class="pre">op</span></tt>:</p>
  70. <pre class="literal-block">
  71. <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( x, op, y );
  72. </pre>
  73. <table class="docutils field-list" frame="void" rules="none">
  74. <col class="field-name" />
  75. <col class="field-body" />
  76. <tbody valign="top">
  77. <tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first">None.</p>
  78. </td>
  79. </tr>
  80. <tr class="field"><th class="field-name">Semantics:</th><td class="field-body"><p class="first">Generates a compilation error if <tt class="literal"><span class="pre">(</span> <span class="pre">x</span> <span class="pre">op</span> <span class="pre">y</span> <span class="pre">)</span> <span class="pre">!=</span> <span class="pre">true</span></tt>, otherwise
  81. has no effect.</p>
  82. <p>When possible within the compiler's diagnostic capabilities,
  83. the error message will include a name of the relation being checked,
  84. the actual values of both operands, and have a general form of:</p>
  85. <pre class="last literal-block">
  86. <em>...</em> ************<em>...</em>assert_relation&lt;op, x, y&gt;::************) <em>...</em>
  87. </pre>
  88. </td>
  89. </tr>
  90. </tbody>
  91. </table>
  92. </div>
  93. <div class="section" id="id1313">
  94. <h3><a class="subsection-title" href="#example" name="example">Example</a></h3>
  95. <pre class="literal-block">
  96. template&lt; typename T, typename U &gt; struct my
  97. {
  98. // ...
  99. <a href="./assert-relation.html" class="identifier">BOOST_MPL_ASSERT_RELATION</a>( sizeof(T), &lt;, sizeof(U) );
  100. };
  101. my&lt;char[50],char[10]&gt; test;
  102. // In instantiation of `my&lt;char[50], char[10]&gt;':
  103. // instantiated from here
  104. // conversion from `
  105. // mpl_::failed************mpl_::assert_relation&lt;<a href="./less.html" class="identifier">less</a>, 50, 10&gt;::************'
  106. // to non-scalar type `mpl_::assert&lt;false&gt;' requested
  107. </pre>
  108. </div>
  109. <div class="section" id="id1314">
  110. <h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
  111. <p><a class="reference internal" href="./asserts.html">Asserts</a>, <a class="reference internal" href="./assert.html">BOOST_MPL_ASSERT</a>, <a class="reference internal" href="./assert-not.html">BOOST_MPL_ASSERT_NOT</a>, <a class="reference internal" href="./assert-msg.html">BOOST_MPL_ASSERT_MSG</a></p>
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  116. <td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div>
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