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

   1 [#first_of]
   2 [section first_of]
   3
   4 [h1 Synopsis]
   5
   6   template <class P1, /* ... */, class Pn>
   7   struct first_of;
   8
   9 This is a [link parser_combinator parser combinator].
  10
  11 [table Arguments
  12   [[Name]         [Type]]
  13   [[`P1` .. `Pn`] [[link parser parser]]]
  14 ]
  15
  16 [h1 Description]
  17
  18 `first_of` applies the `P1` ... `Pn` parsers in sequence. It accepts an input
  19 when all parsers accept it. The result of parsing is the result of the first
  20 parser.
  21
  22 [h1 Header]
  23
  24   #include <boost/metaparse/first_of.hpp>
  25
  26 [h1 Expression semantics]
  27
  28 For any `p1`, ... `pn` parsers
  29
  30   first_of<p1, ..., pn>
  31
  32 is equivalent to
  33
  34   nth_of_c<0, p1, ..., pn>
  35
  36 [h1 Example]
  37
  38   #include <boost/metaparse/first_of.hpp>
  39   #include <boost/metaparse/int_.hpp>
  40   #include <boost/metaparse/lit_c.hpp>
  41   #include <boost/metaparse/string.hpp>
  42   #include <boost/metaparse/start.hpp>
  43   #include <boost/metaparse/is_error.hpp>
  44   #include <boost/metaparse/get_result.hpp>
  45
  46   #include <type_traits>
  47
  48   using namespace boost::metaparse;
  49
  50   using int_with_semicolon = first_of<int_, lit_c<';'>>;
  51
  52   static_assert(
  53     is_error<
  54       int_with_semicolon::apply<BOOST_METAPARSE_STRING("13"), start>
  55     >::type::value,
  56     "int without semicolon is rejected"
  57   );
  58
  59   static_assert(
  60     get_result<
  61       int_with_semicolon::apply<BOOST_METAPARSE_STRING("13;"), start>
  62     >::type::value,
  63     "the result is the result of the first parser"
  64   );
  65
  66 [endsect]
  67