bump version to 12.2.2-pve1

[ceph.git] / ceph / src / boost / libs / metaparse / doc / fail.qbk

[#fail]
[section fail]

[h1 Synopsis]

  template <class Msg>
  struct fail;

This is a [link parser parser].

[table Arguments
  [[Name]  [Type]]
  [[`Msg`] [[link parsing_error_message parsing error message]]]
]

[h1 Description]

Parser rejecting every input.

[h1 Header]

  #include <boost/metaparse/fail.hpp>

[h1 Expression semantics]

For any `msg` parsing error message, `s` compile-time string and `pos` source
position

  fail<msg>::apply<s, pos>::type

returns an error with `msg` as the error message.

[h1 Example]

  #include <boost/metaparse/fail.hpp>
  #include <boost/metaparse/string.hpp>
  #include <boost/metaparse/start.hpp>
  #include <boost/metaparse/is_error.hpp>
  #include <boost/metaparse/get_message.hpp>
  #include <boost/metaparse/define_error.hpp>
  
  using namespace boost::metaparse;
  
  BOOST_METAPARSE_DEFINE_ERROR(sample_error, "This is an example parsing error");
  
  using fail_p = fail<sample_error>;
  
  static_assert(
    is_error<fail_p::apply<BOOST_METAPARSE_STRING("foo"), start>>::type::value,
    "it should reject every input"
  );
  
  static_assert(
    std::is_same<
      get_message<fail_p::apply<BOOST_METAPARSE_STRING("foo"), start>>::type,
      sample_error
    >::type::value,
    "the error message should be the type specified"
  );

[endsect]