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

   1 [#keyword]
   2 [section keyword]
   3
   4 [h1 Synopsis]
   5
   6   template <class S, class ResultType = /* unspecified */>
   7   struct keyword;
   8
   9 This is a [link parser parser].
  10
  11 [table Arguments
  12   [[Name]         [Type]]
  13   [[`S`]          [[link string string]]]
  14   [[`ResultType`] [[link metaprogramming_value template metaprogramming value]]]
  15 ]
  16
  17 [h1 Description]
  18
  19 Parser accepting the keyword `S`. The result of parsing is `ResultType`, which
  20 is optional; when not given, the result of successful parsing is undefined.
  21
  22 [h1 Header]
  23
  24   #include <boost/metaparse/keyword.hpp>
  25
  26 [h1 Expression semantics]
  27
  28 For any `r` class and `s` compile-time string that is built from the characters
  29 `c1` ... `cn` the following are equivalent:
  30
  31   keyword<s, r>
  32
  33   last_of<lit<c1>, /* ... */, lit<cn>, return_<r>>
  34
  35 [h1 Example]
  36
  37   #include <boost/metaparse/keyword.hpp>
  38   #include <boost/metaparse/string.hpp>
  39   #include <boost/metaparse/start.hpp>
  40   #include <boost/metaparse/get_result.hpp>
  41   #include <boost/metaparse/is_error.hpp>
  42
  43   #include <type_traits>
  44
  45   using namespace boost::metaparse;
  46
  47   static_assert(
  48     get_result<
  49       keyword<BOOST_METAPARSE_STRING("for"), std::integral_constant<int, 13>>
  50         ::apply<BOOST_METAPARSE_STRING("for"), start>
  51     >::type::value == 13,
  52     "the result of parsing the keyword is keyword's second argument"
  53   );
  54
  55   static_assert(
  56     is_error<
  57       keyword<BOOST_METAPARSE_STRING("for"), std::integral_constant<int, 13>>
  58         ::apply<BOOST_METAPARSE_STRING("if"), start>
  59     >::type::value,
  60     "a word other than the keyword is an error"
  61   );
  62
  63 [endsect]
  64