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

   1 [#iterate_c]
   2 [section iterate_c]
   3
   4 [h1 Synopsis]
   5
   6   template <class P, int N>
   7   struct iterate_c;
   8
   9 This is a [link parser_combinator parser combinator].
  10
  11 [table Arguments
  12   [[Name] [Type]]
  13   [[`P`]  [[link parser parser]]]
  14   [[`N`]  [non-negative integer value]]
  15 ]
  16
  17 [h1 Description]
  18
  19 It applies `P` on the input string `N` times. The result of parsing is a
  20 sequence of the results of the individual applications of `P`. `P` has to accept
  21 the input `N` times for `iterate_c` to accept it.
  22
  23 [h1 Header]
  24
  25   #include <boost/metaparse/iterate_c.hpp>
  26
  27 [h1 Expression semantics]
  28
  29 For any `p` parser, `n` integer value the following are equivalent:
  30
  31   iterate_c<p, n>
  32
  33   sequence<
  34     p, // 1.
  35     p, // 2.
  36     // ...
  37     p  // n.
  38   >
  39
  40 [h1 Example]
  41
  42   #include <boost/metaparse/iterate_c.hpp>
  43   #include <boost/metaparse/digit.hpp>
  44   #include <boost/metaparse/string.hpp>
  45   #include <boost/metaparse/start.hpp>
  46   #include <boost/metaparse/get_result.hpp>
  47   #include <boost/metaparse/is_error.hpp>
  48
  49   #include <boost/mpl/vector.hpp>
  50   #include <boost/mpl/equal.hpp>
  51   #include <boost/mpl/char.hpp>
  52
  53   using namespace boost::metaparse;
  54
  55   static_assert(
  56     boost::mpl::equal<
  57       boost::mpl::vector<
  58         boost::mpl::char_<'1'>,
  59         boost::mpl::char_<'2'>,
  60         boost::mpl::char_<'3'>
  61       >,
  62       get_result<
  63         iterate_c<digit, 3>::apply<BOOST_METAPARSE_STRING("123"), start>
  64       >::type
  65     >::type::value,
  66     "the result should be the sequence of the individual applications of digit"
  67   );
  68
  69   static_assert(
  70     boost::mpl::equal<
  71       boost::mpl::vector<
  72         boost::mpl::char_<'1'>,
  73         boost::mpl::char_<'2'>,
  74         boost::mpl::char_<'3'>
  75       >,
  76       get_result<
  77         iterate_c<digit, 3>::apply<BOOST_METAPARSE_STRING("1234"), start>
  78       >::type
  79     >::type::value,
  80     "only three iterations should be made"
  81   );
  82
  83   static_assert(
  84     is_error<
  85       iterate_c<digit, 3>::apply<BOOST_METAPARSE_STRING("12"), start>
  86     >::type::value,
  87     "it should fail when digit can not be applied three times"
  88   );
  89
  90 [endsect]
  91