include/boost/url/grammar/variant_rule.hpp

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1		//
2		// Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
3		// Copyright (c) 2022 Alan de Freitas (alandefreitas@gmail.com)
4		//
5		// Distributed under the Boost Software License, Version 1.0. (See accompanying
6		// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7		//
8		// Official repository: https://github.com/boostorg/url
9		//
10
11		#ifndef BOOST_URL_GRAMMAR_VARIANT_RULE_HPP
12		#define BOOST_URL_GRAMMAR_VARIANT_RULE_HPP
13
14		#include <boost/url/detail/config.hpp>
15		#include <boost/url/error_types.hpp>
16		#include <boost/url/variant.hpp>
17		#include <boost/url/grammar/detail/tuple.hpp>
18		#include <boost/url/grammar/type_traits.hpp>
19
20		namespace boost {
21		namespace urls {
22		namespace grammar {
23
24		namespace implementation_defined {
25		template<
26		class R0, class... Rn>
27		class variant_rule_t
28		{
29		public:
30		using value_type = variant2::variant<
31		typename R0::value_type,
32		typename Rn::value_type...>;
33
34		BOOST_URL_CXX20_CONSTEXPR
35		auto
36		parse(
37		char const*& it,
38		char const* end) const ->
39		system::result<value_type>;
40
41		constexpr
42	1	variant_rule_t(
43		R0 const& r0,
44		Rn const&... rn) noexcept
45	1	: rn_(r0, rn...)
46		{
47	1	}
48
49		private:
50
51		detail::tuple<R0, Rn...> rn_;
52		};
53		} // implementation_defined
54
55		/** Match one of a set of rules
56
57		Each specified rule is tried in sequence.
58		When the first match occurs, the result
59		is stored and returned in the variant. If
60		no match occurs, an error is returned.
61
62		@param r0 The first rule to match
63		@param rn A list of one or more rules to match
64		@return The variant rule
65
66		@par Value Type
67		@code
68		using value_type = variant< typename Rules::value_type... >;
69		@endcode
70
71		@par Example
72		Rules are used with the function @ref parse.
73		@code
74		// request-target = origin-form
75		// / absolute-form
76		// / authority-form
77		// / asterisk-form
78
79		system::result< variant< url_view, url_view, authority_view, core::string_view > > rv = grammar::parse(
80		"/index.html?width=full",
81		variant_rule(
82		origin_form_rule,
83		absolute_uri_rule,
84		authority_rule,
85		delim_rule('*') ) );
86		@endcode
87
88		@par BNF
89		@code
90		variant = rule1 / rule2 / rule3...
91		@endcode
92
93		@par Specification
94		@li <a href="https://datatracker.ietf.org/doc/html/rfc5234#section-3.2"
95		>3.2. Alternatives (rfc5234)</a>
96		@li <a href="https://datatracker.ietf.org/doc/html/rfc7230#section-5.3"
97		>5.3. Request Target (rfc7230)</a>
98
99		@see
100		@ref absolute_uri_rule,
101		@ref authority_rule,
102		@ref delim_rule,
103		@ref parse,
104		@ref origin_form_rule,
105		@ref url_view.
106		*/
107		template<
108		BOOST_URL_CONSTRAINT(Rule) R0,
109		BOOST_URL_CONSTRAINT(Rule)... Rn>
110		constexpr
111		auto
112		variant_rule(
113		R0 const& r0,
114		Rn const&... rn) noexcept ->
115		implementation_defined::variant_rule_t<R0, Rn...>;
116
117		} // grammar
118		} // urls
119		} // boost
120
121		#include <boost/url/grammar/impl/variant_rule.hpp>
122
123		#endif
124