[#digit_val]
[section digit_val]

[h1 Synopsis]

  struct digit_val;

This is a [link parser parser].

[h1 Description]

It accepts one character in the range `0-9`. The result of the parser is the
value represented by the accepted character.

[h1 Header]

  #include <boost/metaparse/digit_val.hpp>

[h1 Expression semantics]

The following are equivalent:

  digit_val
  
  transform<digit, util::digit_to_int<>>

[h1 Example]

  #include <boost/metaparse/digit_val.hpp>
  #include <boost/metaparse/start.hpp>
  #include <boost/metaparse/string.hpp>
  #include <boost/metaparse/is_error.hpp>
  #include <boost/metaparse/get_result.hpp>
  
  using namespace boost::metaparse;
  
  static_assert(
    !is_error<digit_val::apply<BOOST_METAPARSE_STRING("0"), start>>::type::value,
    "digit_val should accept a digit"
  );
  
  static_assert(
    is_error<digit_val::apply<BOOST_METAPARSE_STRING("x"), start>>::type::value,
    "digit_val should reject a character"
  );
  
  static_assert(
    get_result<
      digit_val::apply<BOOST_METAPARSE_STRING("0"), start>
    >::type::value == 0,
    "the result of parsing should be the int value"
  );

[endsect]