123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566 |
- [#empty]
- [section empty]
- [h1 Synopsis]
- template <class Result>
- struct empty;
- This is a [link parser parser].
- [table Arguments
- [[Name] [Type]]
- [[`Result`] [[link metaprogramming_value template metaprogramming value]]]
- ]
- [h1 Description]
- It accepts empty input only. The result of parsing is the `Result`
- argument.
- [h1 Header]
- #include <boost/metaparse/empty.hpp>
- [h1 Expression semantics]
- For any `c` class the following are equivalent:
- empty<c>
-
- except<one_char, c, error::end_of_input_expected>
- [h1 Example]
- #include <boost/metaparse/empty.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 want_empty = empty<BOOST_METAPARSE_STRING("result")>;
-
- static_assert(
- !is_error<want_empty::apply<BOOST_METAPARSE_STRING(""), start>>::type::value,
- "empty accepts the empty input"
- );
-
- static_assert(
- is_error<want_empty::apply<BOOST_METAPARSE_STRING("x"), start>>::type::value,
- "empty should reject non-empty input"
- );
-
- static_assert(
- std::is_same<
- get_result<want_empty::apply<BOOST_METAPARSE_STRING(""), start>>::type,
- BOOST_METAPARSE_STRING("result")
- >::type::value,
- "the result of parsing should be the given value"
- );
- [endsect]
|