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

   1 [#one_char]
   2 [section one_char]
   3
   4 [h1 Synopsis]
   5
   6   struct one_char;
   7
   8 This is a [link parser parser].
   9
  10 [h1 Description]
  11
  12 `one_char` accepts one character. The result of parsing is the accepted
  13 character. It fails for empty input.
  14
  15 [h1 Header]
  16
  17   #include <boost/metaparse/one_char.hpp>
  18
  19 [h1 Expression semantics]
  20
  21 For any `s` non-empty compile-time string and `pos` source position the
  22 following are equivalent
  23
  24   get_result<one_char::apply<s, pos>>
  25
  26   boost::mpl::front<s>
  27
  28   get_remaining<one_char::apply<s, pos>>
  29
  30   boost::mpl::pop_front<s>
  31
  32 The value of `get_position<one_char::apply<s, pos>>` depends on the first
  33 character of the sequence and the value of the one parsed before that (which is
  34 stored in the source position). `one_char` updates the source position's `col`
  35 and `line` values based on the new line characters. It detects Linux (`\n`),
  36 Windows (`\r\n`) and Mac (`\r`) line endings.
  37
  38 `one_char::apply<BOOST_METAPARSE_STRING(""), pos>` returns an error for every
  39 `pos` source position.
  40
  41 [h1 Example]
  42
  43   #include <boost/metaparse/one_char.hpp>
  44   #include <boost/metaparse/start.hpp>
  45   #include <boost/metaparse/string.hpp>
  46   #include <boost/metaparse/get_result.hpp>
  47   #include <boost/metaparse/get_remaining.hpp>
  48   #include <boost/metaparse/is_error.hpp>
  49
  50   #include <type_traits>
  51
  52   using namespace boost::metaparse;
  53
  54   static_assert(
  55     get_result<
  56       one_char::apply<BOOST_METAPARSE_STRING("foo"), start>
  57     >::type::value == 'f',
  58     "the result of parsing should be the first character of the input"
  59   );
  60
  61   static_assert(
  62     std::is_same<
  63       BOOST_METAPARSE_STRING("oo"),
  64       get_remaining<one_char::apply<BOOST_METAPARSE_STRING("foo"), start>>::type
  65     >::type::value,
  66     "one_char should consume the first character of the input"
  67   );
  68
  69   static_assert(
  70     is_error<one_char::apply<BOOST_METAPARSE_STRING(""), start>>::type::value,
  71     "it should return an error for empty input"
  72   );
  73
  74 [endsect]
  75