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

   1 [#transform_error_message]
   2 [section transform_error_message]
   3
   4 [h1 Synopsis]
   5
   6   template <class P, class F>
   7   struct transform_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   [[`F`]  [[link metafunction_class template metafunction class] taking one argument]]
  15 ]
  16
  17 [h1 Description]
  18
  19 It parses the input with `P`. When this succeeds, the result of parsing with
  20 `transform_error_message` will be the result of parsing with `P`. When it fails,
  21 the error `P` returns is forwarded to the caller of `transform_error_message`,
  22 but the message of it is transformed with `F`.
  23
  24 [h1 Header]
  25
  26   #include <boost/metaparse/transform_error_message.hpp>
  27
  28 [h1 Expression semantics]
  29
  30 For any `p` parser and `f` metafunction class accepting one argument
  31
  32   transform_error_message<p, f>::apply<s, pos>
  33
  34 is equivalent to `p::apply<s, pos>` when `p` accepts the input.
  35 It is equivalent to
  36 `reject<f::apply<get_message<p::apply<s, pos>>::type>, get_position<p::apply<s, pos>>>`
  37 otherwise.
  38
  39 [h1 Example]
  40
  41   #include <boost/metaparse/transform_error_message.hpp>
  42   #include <boost/metaparse/repeated1.hpp>
  43   #include <boost/metaparse/letter.hpp>
  44   #include <boost/metaparse/keyword.hpp>
  45   #include <boost/metaparse/last_of.hpp>
  46   #include <boost/metaparse/token.hpp>
  47   #include <boost/metaparse/string.hpp>
  48   #include <boost/metaparse/is_error.hpp>
  49   #include <boost/metaparse/start.hpp>
  50   #include <boost/metaparse/get_message.hpp>
  51   #include <boost/metaparse/define_error.hpp>
  52   #include <boost/metaparse/reject.hpp>
  53
  54   #include <type_traits>
  55
  56   using namespace boost::metaparse;
  57
  58   BOOST_METAPARSE_DEFINE_ERROR(name_expected, "Name expected");
  59
  60   struct return_name_expected
  61   {
  62     typedef return_name_expected type;
  63
  64     template <class>
  65     struct apply : name_expected {};
  66   };
  67
  68   using keyword_name = token<keyword<BOOST_METAPARSE_STRING("name")>>;
  69   using name_token = token<repeated1<letter>>;
  70
  71   using name_parser =
  72     last_of<
  73       keyword_name,
  74       transform_error_message<name_token, return_name_expected>
  75     >;
  76
  77   static_assert(
  78     !is_error<
  79       name_parser::apply<BOOST_METAPARSE_STRING("name Bela"), start>
  80     >::type::value,
  81     "name_parser should accept \"name <a name>\""
  82   );
  83
  84   static_assert(
  85     is_error<
  86       name_parser::apply<BOOST_METAPARSE_STRING("name ?"), start>
  87     >::type::value,
  88     "name_parser should reject input when name is a question mark"
  89   );
  90
  91   static_assert(
  92     std::is_same<
  93       get_message<
  94         name_parser::apply<BOOST_METAPARSE_STRING("name ?"), start>
  95       >::type,
  96       name_expected
  97     >::type::value,
  98     "the error message should be the one specified by change_error_message"
  99   );
 100
 101 [endsect]
 102