[#one_of_c]
[section one_of_c]

[h1 Synopsis]

  template <char... Cs>
  struct one_of_c;

This is a [link parser parser].

[table Arguments
  [[Name] [Type]]
  [[`Cs`] [character values]]
]

[h1 Description]

It accepts inputs beginning with any of the `Cs...` characters. The result of
parsing is the first character of the input.

On compilers, which are not C++11-compliant, the maximum number of characters
that can be provided is defined by the `BOOST_METAPARSE_LIMIT_ONE_OF_SIZE`
macro. Its default value is `20`.

[h1 Header]

  #include <boost/metaparse/one_of_c.hpp>

[h1 Expression semantics]

For any `c1`, ..., `cn` characters

  one_of_c<c1, ..., cn>

is equivalent to

  one_of<lit_c<c1>, /* ... */, lit_c<cn>>

[h1 Example]

  #include <boost/metaparse/one_of_c.hpp>
  #include <boost/metaparse/start.hpp>
  #include <boost/metaparse/string.hpp>
  #include <boost/metaparse/get_result.hpp>
  #include <boost/metaparse/is_error.hpp>
  
  using namespace boost::metaparse;
  
  using whitespace = one_of_c<' ', '\n', '\r', '\t', '\v'>;
  
  static_assert(
    get_result<
      whitespace::apply<BOOST_METAPARSE_STRING(" "), start>
    >::type::value == ' ',
    "the result of parsing should be the first character of the input"
  );
  
  static_assert(
    is_error<whitespace::apply<BOOST_METAPARSE_STRING("x"), start>>::type::value,
    "it should return an error when the input does not begin with a whitespace"
  );

[endsect]