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

   1 [#fail]
   2 [section fail]
   3
   4 [h1 Synopsis]
   5
   6   template <class Msg>
   7   struct fail;
   8
   9 This is a [link parser parser].
  10
  11 [table Arguments
  12   [[Name]  [Type]]
  13   [[`Msg`] [[link parsing_error_message parsing error message]]]
  14 ]
  15
  16 [h1 Description]
  17
  18 Parser rejecting every input.
  19
  20 [h1 Header]
  21
  22   #include <boost/metaparse/fail.hpp>
  23
  24 [h1 Expression semantics]
  25
  26 For any `msg` parsing error message, `s` compile-time string and `pos` source
  27 position
  28
  29   fail<msg>::apply<s, pos>::type
  30
  31 returns an error with `msg` as the error message.
  32
  33 [h1 Example]
  34
  35   #include <boost/metaparse/fail.hpp>
  36   #include <boost/metaparse/string.hpp>
  37   #include <boost/metaparse/start.hpp>
  38   #include <boost/metaparse/is_error.hpp>
  39   #include <boost/metaparse/get_message.hpp>
  40   #include <boost/metaparse/define_error.hpp>
  41
  42   using namespace boost::metaparse;
  43
  44   BOOST_METAPARSE_DEFINE_ERROR(sample_error, "This is an example parsing error");
  45
  46   using fail_p = fail<sample_error>;
  47
  48   static_assert(
  49     is_error<fail_p::apply<BOOST_METAPARSE_STRING("foo"), start>>::type::value,
  50     "it should reject every input"
  51   );
  52
  53   static_assert(
  54     std::is_same<
  55       get_message<fail_p::apply<BOOST_METAPARSE_STRING("foo"), start>>::type,
  56       sample_error
  57     >::type::value,
  58     "the error message should be the type specified"
  59   );
  60
  61 [endsect]
  62