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

   1 [#get_prev_char]
   2 [section get_prev_char]
   3
   4 [h1 Synopsis]
   5
   6   template <class SourcePosition>
   7   struct get_prev_char;
   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 ]
  15
  16 [h1 Description]
  17
  18 Returns the last character the source position was updated with. The value it
  19 returns for [link start `start`] is unspecified.
  20
  21 [h1 Header]
  22
  23   #include <boost/metaparse/get_prev_char.hpp>
  24
  25 [h1 Expression semantics]
  26
  27 For any `l`, `c` compile-time wrapped integral values and `ch` compile-time
  28 wrapped character the following are equivalent
  29
  30   get_prev_char<source_position<l, c, ch>>::type
  31
  32   ch::type
  33
  34 [h1 Example]
  35
  36   #include <boost/metaparse/get_prev_char.hpp>
  37   #include <boost/metaparse/source_position.hpp>
  38
  39   #include <type_traits>
  40
  41   using namespace boost::metaparse;
  42
  43   struct returns_source_position
  44   {
  45     using type =
  46       source_position<
  47         std::integral_constant<int, 11>,
  48         std::integral_constant<int, 13>,
  49         std::integral_constant<char, 'x'>
  50       >;
  51   };
  52
  53   static_assert(
  54     get_prev_char<
  55       source_position<
  56         std::integral_constant<int, 11>,
  57         std::integral_constant<int, 13>,
  58         std::integral_constant<char, 'x'>
  59       >
  60     >::type::value == 'x',
  61     "It should return the prev. char of a source position"
  62   );
  63
  64   static_assert(
  65     get_prev_char<returns_source_position>::type::value == 'x',
  66     "It should support lazy evaluation"
  67   );
  68
  69 [endsect]
  70