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- [#first_of]
- [section first_of]
- [h1 Synopsis]
- template <class... Ps>
- struct first_of;
- This is a [link parser_combinator parser combinator].
- [table Arguments
- [[Name] [Type]]
- [[`Ps`] [[link parser parser]s]]
- ]
- [h1 Description]
- `first_of` applies the `Ps...` parsers in sequence. It accepts an input when all
- parsers accept it. The result of parsing is the result of the first parser.
- On compilers, which are not C++11-compliant, the maximum number of parsers
- `first_of` accepts can be specified with the
- `BOOST_METAPARSE_LIMIT_SEQUENCE_SIZE` macro. Its default value is `5`.
- [h1 Header]
- #include <boost/metaparse/first_of.hpp>
- [h1 Expression semantics]
- For any `p1`, ... `pn` parsers
- first_of<p1, ..., pn>
- is equivalent to
- nth_of_c<0, p1, ..., pn>
- [h1 Example]
- #include <boost/metaparse/first_of.hpp>
- #include <boost/metaparse/int_.hpp>
- #include <boost/metaparse/lit_c.hpp>
- #include <boost/metaparse/string.hpp>
- #include <boost/metaparse/start.hpp>
- #include <boost/metaparse/is_error.hpp>
- #include <boost/metaparse/get_result.hpp>
-
- #include <type_traits>
-
- using namespace boost::metaparse;
-
- using int_with_semicolon = first_of<int_, lit_c<';'>>;
-
- static_assert(
- is_error<
- int_with_semicolon::apply<BOOST_METAPARSE_STRING("13"), start>
- >::type::value,
- "int without semicolon is rejected"
- );
-
- static_assert(
- get_result<
- int_with_semicolon::apply<BOOST_METAPARSE_STRING("13;"), start>
- >::type::value,
- "the result is the result of the first parser"
- );
- [endsect]
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