1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283 |
- [#except]
- [section except]
- [h1 Synopsis]
- template <class P, class Result, class ErrorMsg>
- struct except;
- This is a [link parser_combinator parser combinator].
- [table Arguments
- [[Name] [Type]]
- [[`P`] [[link parser parser]]]
- [[`Result`] [[link metaprogramming_value template metaprogramming value]]]
- [[`ErrorMsg`] [[link parsing_error_message parsing error message]]]
- ]
- [h1 Description]
- `except` accepts the input when `P` rejects it and the result of parsing is the
- `Result` argument. When `P` accepts the input, `except` rejects it and the
- reason is `ErrorMsg`.
- [h1 Header]
- #include <boost/metaparse/except.hpp>
- [h1 Expression semantics]
- For any `p` parser, `c` class, `msg` parsing error message, `s` compile-time
- string and `pos` source position the following are equivalent
- get_result<except<p, c, msg>, s, pos>::type
- c
- get_remaining<except<p, c, msg>, s, pos>::type
- s
- get_position<except<p, c, msg>, s, pos>::type
- pos
- when `p` rejects the input. The result of the parser is an error with the error
- message `msg` otherwise.
- [h1 Example]
- #include <boost/metaparse/except.hpp>
- #include <boost/metaparse/int_.hpp>
- #include <boost/metaparse/string.hpp>
- #include <boost/metaparse/start.hpp>
- #include <boost/metaparse/get_result.hpp>
- #include <boost/metaparse/get_message.hpp>
- #include <boost/metaparse/define_error.hpp>
-
- #include <type_traits>
-
- using namespace boost::metaparse;
-
- BOOST_METAPARSE_DEFINE_ERROR(
- number_is_not_allowed,
- "numbers are not allowed here"
- );
-
- using except_int =
- except<int_, std::integral_constant<int, 1>, number_is_not_allowed>;
-
- static_assert(
- get_result<
- except_int::apply<BOOST_METAPARSE_STRING("foo"), start>
- >::type::value == 1,
- "it should accept the input when it is not an integer"
- );
-
- static_assert(
- std::is_same<
- number_is_not_allowed,
- get_message<except_int::apply<BOOST_METAPARSE_STRING("13"), start>>::type
- >::type::value,
- "it should reject the input when it is an integer"
- );
- [endsect]
|