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3rdparty/boost_1_81_0/libs/metaparse/doc/range.qbk 1.51 KB
73ef4ff3   Hu Chunming   提交三方库
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  [#range]
  [section range]
  
  [h1 Synopsis]
  
    template <class From, class To>
    struct range;
  
  This is a [link parser parser].
  
  [table Arguments
    [[Name]   [Type]]
    [[`From`] [[link boxed_value boxed] character value]]
    [[`To`]   [[link boxed_value boxed] character value]]
  ]
  
  [h1 Description]
  
  `range` accepts one character in the range `[From..To]`. The result of the
  parser is the accepted character.
  
  [h1 Header]
  
    #include <boost/metaparse/range.hpp>
  
  [h1 Expression semantics]
  
  For any `A`, `B` wrapped characters the following are equivalent:
  
    range<A, B>
    
    accept_when<one_char, util::in_range<A, B>, errors::unexpected_character>
  
  [h1 Example]
  
    #include <boost/metaparse/range.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;
    
    using one_digit =
      range<std::integral_constant<char, '0'>, std::integral_constant<char, '9'>>;
    
    static_assert(
      !is_error<one_digit::apply<BOOST_METAPARSE_STRING("0"), start>>::type::value,
      "one_digit should accept a digit"
    );
    
    static_assert(
      is_error<one_digit::apply<BOOST_METAPARSE_STRING("x"), start>>::type::value,
      "one_digit should reject a value outside of ['0'..'9']"
    );
    
    static_assert(
      get_result<
        one_digit::apply<BOOST_METAPARSE_STRING("0"), start>
      >::type::value == '0',
      "the result of parsing should be the character value"
    );
  
  [endsect]