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

   1 [#change_error_message]
   2 [section change_error_message]
   3
   4 [h1 Synopsis]
   5
   6   template <class P, class Msg>
   7   struct change_error_message;
   8
   9 This is a [link parser_combinator parser combinator].
  10
  11 [table Arguments
  12   [[Name]  [Type]]
  13   [[`P`]   [[link parser parser]]]
  14   [[`Msg`] [[link parsing_error_message parsing error message]]]
  15 ]
  16
  17 [h1 Description]
  18
  19 It applies `P` on the input. When `P` succeeds, `change_error_message` returns
  20 the result `P` returns, otherwise `change_error_message` rejects the input and
  21 the reason will be `Msg`.
  22
  23 [h1 Header]
  24
  25   #include <boost/metaparse/change_error_message.hpp>
  26
  27 [h1 Expression semantics]
  28
  29 For any `p` parser and `m` parsing error message, `s` compile-time string and
  30 `pos` source position
  31
  32   change_error_message<p, msg>::apply<s, pos>
  33
  34 is equivalent to `p::apply<s, pos>` when `p` accepts the input.
  35 It is equivalent to `fail<msg>::apply<s, pos>` otherwise.
  36
  37 [h1 Example]
  38
  39   #include <boost/metaparse/change_error_message.hpp>
  40   #include <boost/metaparse/repeated1.hpp>
  41   #include <boost/metaparse/letter.hpp>
  42   #include <boost/metaparse/keyword.hpp>
  43   #include <boost/metaparse/last_of.hpp>
  44   #include <boost/metaparse/token.hpp>
  45   #include <boost/metaparse/string.hpp>
  46   #include <boost/metaparse/is_error.hpp>
  47   #include <boost/metaparse/start.hpp>
  48   #include <boost/metaparse/get_message.hpp>
  49   #include <boost/metaparse/define_error.hpp>
  50
  51   #include <type_traits>
  52
  53   using namespace boost::metaparse;
  54
  55   BOOST_METAPARSE_DEFINE_ERROR(name_expected, "Name expected");
  56
  57   using keyword_name = token<keyword<BOOST_METAPARSE_STRING("name")>>;
  58   using name_token = token<repeated1<letter>>;
  59
  60   using name_parser =
  61     last_of<keyword_name, change_error_message<name_token, name_expected>>;
  62
  63   static_assert(
  64     !is_error<
  65       name_parser::apply<BOOST_METAPARSE_STRING("name Bela"), start>
  66     >::type::value,
  67     "name_parser should accept \"name <a name>\""
  68   );
  69
  70   static_assert(
  71     is_error<
  72       name_parser::apply<BOOST_METAPARSE_STRING("name ?"), start>
  73     >::type::value,
  74     "name_parser should reject input when name is a question mark"
  75   );
  76
  77   static_assert(
  78     std::is_same<
  79       get_message<
  80         name_parser::apply<BOOST_METAPARSE_STRING("name ?"), start>
  81       >::type,
  82       name_expected
  83     >::type::value,
  84     "the error message should be the one specified by change_error_message"
  85   );
  86
  87 [endsect]
  88