Synopsis

template <class C>
struct return_;

This is a parser.

Description

return_ accepts every input. The result of parsing is C, the remaining string is the input string.

Header

#include <boost/metaparse/return_.hpp>

Expression semantics

For any c class, s compile-time string and pos source position the following are equivalent

get_result<return_<c>::apply<s, pos>>::type

c

get_remaining<return_<c>::apply<s, pos>>::type

s

get_position<return_<c>::apply<s, pos>>::type

pos

Example

#include <boost/metaparse/return_.hpp>
#include <boost/metaparse/int_.hpp>
#include <boost/metaparse/one_of.hpp>
#include <boost/metaparse/start.hpp>
#include <boost/metaparse/string.hpp>
#include <boost/metaparse/get_result.hpp>

#include <type_traits>

using namespace boost::metaparse;

using default_value = std::integral_constant<int, 13>;

using optional_number = one_of<int_, return_<default_value>>;

static_assert(
  get_result<
    optional_number::apply<BOOST_METAPARSE_STRING("11"), start>
  >::type::value == 11,
  "when a number is provided, it is the result of parsing"
);

static_assert(
  get_result<
    optional_number::apply<BOOST_METAPARSE_STRING(""), start>
  >::type::value == 13,
  "when no number is provided, the default value is the result of parsing"
);