75 lines
1.5 KiB
Plaintext
75 lines
1.5 KiB
Plaintext
[#return_]
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[section return_]
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[h1 Synopsis]
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template <class C>
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struct return_;
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This is a [link parser parser].
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[table Arguments
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[[Name] [Type]]
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[[`C`] [[link metaprogramming_value template metaprogramming value]]]
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]
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[h1 Description]
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`return_` accepts every input. The result of parsing is `C`, the remaining
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string is the input string.
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[h1 Header]
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#include <boost/metaparse/return_.hpp>
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[h1 Expression semantics]
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For any `c` class, `s` compile-time string and `pos` source position the
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following are equivalent
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get_result<return_<c>::apply<s, pos>>::type
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c
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get_remaining<return_<c>::apply<s, pos>>::type
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s
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get_position<return_<c>::apply<s, pos>>::type
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pos
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[h1 Example]
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#include <boost/metaparse/return_.hpp>
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#include <boost/metaparse/int_.hpp>
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#include <boost/metaparse/one_of.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 <type_traits>
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using namespace boost::metaparse;
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using default_value = std::integral_constant<int, 13>;
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using optional_number = one_of<int_, return_<default_value>>;
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static_assert(
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get_result<
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optional_number::apply<BOOST_METAPARSE_STRING("11"), start>
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>::type::value == 11,
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"when a number is provided, it is the result of parsing"
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);
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static_assert(
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get_result<
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optional_number::apply<BOOST_METAPARSE_STRING(""), start>
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>::type::value == 13,
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"when no number is provided, the default value is the result of parsing"
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);
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[endsect]
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