url/grammar/variant_rule.hpp

0001 //
0002 // Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
0003 //
0004 // Distributed under the Boost Software License, Version 1.0. (See accompanying
0005 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0006 //
0007 // Official repository: https://github.com/boostorg/url
0008 //
0009
0010 #ifndef BOOST_URL_GRAMMAR_VARIANT_RULE_HPP
0011 #define BOOST_URL_GRAMMAR_VARIANT_RULE_HPP
0012
0013 #include <boost/url/detail/config.hpp>
0014 #include <boost/url/error_types.hpp>
0015 #include <boost/url/variant.hpp>
0016 #include <boost/url/grammar/detail/tuple.hpp>
0017 #include <boost/url/grammar/type_traits.hpp>
0018
0019 namespace boost {
0020 namespace urls {
0021 namespace grammar {
0022
0023 namespace implementation_defined {
0024 template<
0025     class R0, class... Rn>
0026 class variant_rule_t
0027 {
0028 public:
0029     using value_type = variant2::variant<
0030         typename R0::value_type,
0031         typename Rn::value_type...>;
0032
0033     auto
0034     parse(
0035         char const*& it,
0036         char const* end) const ->
0037             system::result<value_type>;
0038
0039     constexpr
0040     variant_rule_t(
0041         R0 const& r0,
0042         Rn const&... rn) noexcept
0043         : rn_(r0, rn...)
0044     {
0045     }
0046
0047 private:
0048
0049     detail::tuple<R0, Rn...> rn_;
0050 };
0051 } // implementation_defined
0052
0053 /** Match one of a set of rules
0054
0055     Each specified rule is tried in sequence.
0056     When the first match occurs, the result
0057     is stored and returned in the variant. If
0058     no match occurs, an error is returned.
0059
0060     @param r0 The first rule to match
0061     @param rn A list of one or more rules to match
0062     @return The variant rule
0063
0064     @par Value Type
0065     @code
0066     using value_type = variant< typename Rules::value_type... >;
0067     @endcode
0068
0069     @par Example
0070     Rules are used with the function @ref parse.
0071     @code
0072     // request-target = origin-form
0073     //                / absolute-form
0074     //                / authority-form
0075     //                / asterisk-form
0076
0077     system::result< variant< url_view, url_view, authority_view, core::string_view > > rv = grammar::parse(
0078         "/index.html?width=full",
0079         variant_rule(
0080             origin_form_rule,
0081             absolute_uri_rule,
0082             authority_rule,
0083             delim_rule('*') ) );
0084     @endcode
0085
0086     @par BNF
0087     @code
0088     variant     = rule1 / rule2 / rule3...
0089     @endcode
0090
0091     @par Specification
0092     @li <a href="https://datatracker.ietf.org/doc/html/rfc5234#section-3.2"
0093         >3.2.  Alternatives (rfc5234)</a>
0094     @li <a href="https://datatracker.ietf.org/doc/html/rfc7230#section-5.3"
0095         >5.3.  Request Target (rfc7230)</a>
0096
0097     @see
0098         @ref absolute_uri_rule,
0099         @ref authority_rule,
0100         @ref delim_rule,
0101         @ref parse,
0102         @ref origin_form_rule,
0103         @ref url_view.
0104 */
0105 template<
0106     BOOST_URL_CONSTRAINT(Rule) R0,
0107     BOOST_URL_CONSTRAINT(Rule)... Rn>
0108 constexpr
0109 auto
0110 variant_rule(
0111     R0 const& r0,
0112     Rn const&... rn) noexcept ->
0113         implementation_defined::variant_rule_t<R0, Rn...>;
0114
0115 } // grammar
0116 } // urls
0117 } // boost
0118
0119 #include <boost/url/grammar/impl/variant_rule.hpp>
0120
0121 #endif