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3rdparty/boost_1_81_0/libs/metaparse/doc/lit.qbk 1.48 KB
73ef4ff3   Hu Chunming   提交三方库
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  [#lit]
  [section lit]
  
  [h1 Synopsis]
  
    template <class C>
    struct lit;
  
  This is a [link parser parser].
  
  [table Arguments
    [[Name] [Type]]
    [[`C`]  [[link boxed_value boxed] character value]]
  ]
  
  [h1 Description]
  
  Parser accepting only the `C` character. The result of parsing is the accepted
  character.
  
  [h1 Header]
  
    #include <boost/metaparse/lit.hpp>
  
  [h1 Expression semantics]
  
  For any `c` boxed character the following are equivalent:
  
    lit<c>
    
    accept_when<
      one_char,
      boost::mpl::lambda<boost::mpl::equal_to<boost::mpl::_1, c>>::type,
      error::literal_expected<c::type::value>
    >
  
  [h1 Example]
  
    #include <boost/metaparse/lit.hpp>
    #include <boost/metaparse/start.hpp>
    #include <boost/metaparse/string.hpp>
    #include <boost/metaparse/is_error.hpp>
    #include <boost/metaparse/get_result.hpp>
    
    #include <type_traits>
    
    using namespace boost::metaparse;
    
    static_assert(
      is_error<
        lit<std::integral_constant<char, 'x'>>
          ::apply<BOOST_METAPARSE_STRING("a"), start>
      >::type::value,
      "a different character should be an error"
    );
    
    static_assert(
      is_error<
        lit<std::integral_constant<char, 'x'>>
          ::apply<BOOST_METAPARSE_STRING(""), start>
      >::type::value,
      "empty input should be an error"
    );
    
    static_assert(
      get_result<
        lit<std::integral_constant<char, 'x'>>
          ::apply<BOOST_METAPARSE_STRING("x"), start>
      >::type::value == 'x',
      "result of parsing should be the accepted character"
    );
  
  [endsect]