preprocessor/doc/reference/empty_8hpp.html

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<hr><h1>empty.hpp File Reference</h1><a href="../../../../boost/preprocessor/empty.hpp">Click here to see the header.</a>. 
<a href="#_details">More...</a>
<p>
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<tr><td colspan=2><br><h2>Defines</h2></td></tr>
<tr><td nowrap align=right valign=top>#define&nbsp;</td><td valign=bottom><a class="el" href="empty_8hpp.html#a0">BOOST_PP_EMPTY</a>()</td></tr>
<tr><td>&nbsp;</td><td><font size=-1><em>Expands to nothing.</em> <a href="#a0">More...</a><em></em></font><br><br></td></tr>
<tr><td nowrap align=right valign=top>#define&nbsp;</td><td valign=bottom><a class="el" href="empty_8hpp.html#a1">BOOST_PREPROCESSOR_EMPTY</a>()</td></tr>
<tr><td>&nbsp;</td><td><font size=-1><em>Obsolete.</em> <a href="#a1">More...</a><em></em></font><br><br></td></tr>
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<hr><a name="_details"></a><h2>Detailed Description</h2>
<a href="../../../../boost/preprocessor/empty.hpp">Click here to see the header.</a>.
<p>

<p>
<hr><h2>Define Documentation</h2>
<a name="a0" doxytag="empty.hpp::BOOST_PP_EMPTY"></a><p>
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          <td class="md" nowrap valign="top"> #define BOOST_PP_EMPTY</td>
          <td class="md" valign="top">(&nbsp;</td>
&nbsp;</td>
          <td class="mdname1" valign="top" nowrap>&nbsp;          </td>
          <td class="md" valign="top">)&nbsp;</td>
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<p>
Expands to nothing.
<p>
Used with <a class="el" href="if_8hpp.html#a0">BOOST_PP_IF</a>() and as an unused parameter.
<p>
Example usage as the implementation of <a class="el" href="comma__if_8hpp.html#a0">BOOST_PP_COMMA_IF</a>(C):
<p>
<pre><div class="fragment"><pre>
  #define BOOST_PP_COMMA_IF(C)\
    BOOST_PP_IF(C,BOOST_PP_COMMA,BOOST_PP_EMPTY)()
</pre></div></pre>
<p>
Example usage as an unused macro parameter:
<p>
<pre><div class="fragment"><pre>
  #define BOOST_PP_DEF(CV)\
    template&lt;class base&gt;            \
    CV typename implement_subscript_using_begin_subscript&lt;base&gt;::value_type&amp;\
      implement_subscript_using_begin_subscript&lt;base&gt;::operator[]\
      ( index_type                  \
          i                         \
      ) CV                          \
    { return base::begin()[i];      \
    }

  BOOST_PP_DEF(BOOST_PP_EMPTY())
  BOOST_PP_DEF(const)
  #undef BOOST_PP_DEF
</pre></div></pre>
<p>
The above expands to:
<p>
<pre><div class="fragment"><pre>
  template&lt;class base&gt;
  typename implement_subscript_using_begin_subscript&lt;base&gt;::value_type&amp;
    implement_subscript_using_begin_subscript&lt;base&gt;::operator[]
    ( index_type
        i
    )
  { return base::begin()[i];
  }

  template&lt;class base&gt;
  const typename implement_subscript_using_begin_subscript&lt;base&gt;::value_type&amp;
    implement_subscript_using_begin_subscript&lt;base&gt;::operator[]
    ( index_type
        i
    ) const
  { return base::begin()[i];
  }
</pre></div></pre>
<p>
In case you wonder, the above code is part of a generalized layer for implementing the subscripting operators of a random access container.     </td>
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<a name="a1" doxytag="empty.hpp::BOOST_PREPROCESSOR_EMPTY"></a><p>
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          <td class="md" nowrap valign="top"> #define BOOST_PREPROCESSOR_EMPTY</td>
          <td class="md" valign="top">(&nbsp;</td>
&nbsp;</td>
          <td class="mdname1" valign="top" nowrap>&nbsp;          </td>
          <td class="md" valign="top">)&nbsp;</td>
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<p>
Obsolete.
<p>
Use <a class="el" href="empty_8hpp.html#a0">BOOST_PP_EMPTY</a>().     </td>
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<hr>
<p><EFBFBD> Copyright Housemarque Oy 2001</p>
<p>Permission to copy, use, modify, sell and distribute this document is granted 
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  "as is" without express or implied warranty, and with no claim as to its suitability 
  for any purpose. </p>

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