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- [#one_char]
- [section one_char]
- [h1 Synopsis]
- struct one_char;
- This is a [link parser parser].
- [h1 Description]
- `one_char` accepts one character. The result of parsing is the accepted
- character. It fails for empty input.
- [h1 Header]
- #include <boost/metaparse/one_char.hpp>
- [h1 Expression semantics]
- For any `s` non-empty compile-time string and `pos` source position the
- following are equivalent
- get_result<one_char::apply<s, pos>>
-
- boost::mpl::front<s>
- get_remaining<one_char::apply<s, pos>>
-
- boost::mpl::pop_front<s>
- The value of `get_position<one_char::apply<s, pos>>` depends on the first
- character of the sequence and the value of the one parsed before that (which is
- stored in the source position). `one_char` updates the source position's `col`
- and `line` values based on the new line characters. It detects Linux (`\n`),
- Windows (`\r\n`) and Mac (`\r`) line endings.
- `one_char::apply<BOOST_METAPARSE_STRING(""), pos>` returns an error for every
- `pos` source position.
- [h1 Example]
- #include <boost/metaparse/one_char.hpp>
- #include <boost/metaparse/start.hpp>
- #include <boost/metaparse/string.hpp>
- #include <boost/metaparse/get_result.hpp>
- #include <boost/metaparse/get_remaining.hpp>
- #include <boost/metaparse/is_error.hpp>
-
- #include <type_traits>
-
- using namespace boost::metaparse;
-
- static_assert(
- get_result<
- one_char::apply<BOOST_METAPARSE_STRING("foo"), start>
- >::type::value == 'f',
- "the result of parsing should be the first character of the input"
- );
-
- static_assert(
- std::is_same<
- BOOST_METAPARSE_STRING("oo"),
- get_remaining<one_char::apply<BOOST_METAPARSE_STRING("foo"), start>>::type
- >::type::value,
- "one_char should consume the first character of the input"
- );
-
- static_assert(
- is_error<one_char::apply<BOOST_METAPARSE_STRING(""), start>>::type::value,
- "it should return an error for empty input"
- );
- [endsect]
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