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