ceph/src/boost/libs/metaparse/doc/next_line.qbk

   1 [#next_line]
   2 [section next_line]
   3
   4 [h1 Synopsis]
   5
   6   template <class SourcePosition, class Ch>
   7   struct next_line;
   8
   9 This is a [link lazy_metafunction lazy template metafunction].
  10
  11 [table Arguments
  12   [[Name]             [Type]]
  13   [[`SourcePosition`] [[link source_position source position]]]
  14   [[`Ch`]             [[link boxed_value boxed] character value. The character `SourcePosition` points to in the input.]]
  15 ]
  16
  17 [h1 Description]
  18
  19 Returns a new source position, pointing to the beginning of the next line.
  20
  21 [h1 Header]
  22
  23   #include <boost/metaparse/next_line.hpp>
  24
  25 [h1 Expression semantics]
  26
  27 For any `s` source position and `c` wrapped character the following are
  28 equivalent
  29
  30   get_col<next_line<s, c>>::type
  31
  32   boost::mpl::int_<1>
  33
  34   get_line<next_line<s, c>>
  35
  36   boost::mpl::plus<get_line<s>::type, boost::mpl::int_<1>>
  37
  38   get_prev_char<next_line<s, c>>::type
  39
  40   c
  41
  42 [h1 Example]
  43
  44   #include <boost/metaparse/next_line.hpp>
  45   #include <boost/metaparse/source_position.hpp>
  46   #include <boost/metaparse/get_col.hpp>
  47   #include <boost/metaparse/get_line.hpp>
  48   #include <boost/metaparse/get_prev_char.hpp>
  49
  50   #include <type_traits>
  51
  52   using namespace boost::metaparse;
  53
  54   struct returns_source_position
  55   {
  56     using type =
  57       source_position<
  58         std::integral_constant<int, 11>,
  59         std::integral_constant<int, 13>,
  60         std::integral_constant<char, 'a'>
  61       >;
  62   };
  63
  64   struct returns_char
  65   {
  66     using type = std::integral_constant<char, '\n'>;
  67   };
  68
  69   static_assert(
  70     get_col<
  71       next_line<
  72         source_position<
  73           std::integral_constant<int, 11>,
  74           std::integral_constant<int, 13>,
  75           std::integral_constant<char, 'a'>
  76         >,
  77         std::integral_constant<char, '\n'>
  78       >
  79     >::type::value == 1,
  80     "it should set the column to 1"
  81   );
  82
  83   static_assert(
  84     get_line<
  85       next_line<
  86         source_position<
  87           std::integral_constant<int, 11>,
  88           std::integral_constant<int, 13>,
  89           std::integral_constant<char, 'a'>
  90         >,
  91         std::integral_constant<char, '\n'>
  92       >
  93     >::type::value == 12,
  94     "it should increase the line component of the source position"
  95   );
  96
  97   static_assert(
  98     get_prev_char<
  99       next_line<
 100         source_position<
 101           std::integral_constant<int, 11>,
 102           std::integral_constant<int, 13>,
 103           std::integral_constant<char, 'a'>
 104         >,
 105         std::integral_constant<char, '\n'>
 106       >
 107     >::type::value == '\n',
 108     "it should update the prev char component of the source position"
 109   );
 110
 111   static_assert(
 112     get_col<next_line<returns_source_position, returns_char>>::type::value == 1,
 113     "it should support lazy evaluation"
 114   );
 115
 116 [endsect]
 117