libs/url/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		//
4		// Distributed under the Boost Software License, Version 1.0. (See accompanying
5		// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6		//
7		// Official repository: https://github.com/boostorg/url
8		//
9
10		#ifndef BOOST_URL_GRAMMAR_VARIANT_RULE_HPP
11		#define BOOST_URL_GRAMMAR_VARIANT_RULE_HPP
12
13		#include <boost/url/detail/config.hpp>
14		#include <boost/url/error_types.hpp>
15		#include <boost/url/variant.hpp>
16		#include <boost/url/grammar/detail/tuple.hpp>
17		#include <boost/url/grammar/type_traits.hpp>
18
19		namespace boost {
20		namespace urls {
21		namespace grammar {
22
23		namespace implementation_defined {
24		template<
25		class R0, class... Rn>
26		class variant_rule_t
27		{
28		public:
29		using value_type = variant2::variant<
30		typename R0::value_type,
31		typename Rn::value_type...>;
32
33		auto
34		parse(
35		char const*& it,
36		char const* end) const ->
37		system::result<value_type>;
38
39		constexpr
40	2632	variant_rule_t(
41		R0 const& r0,
42		Rn const&... rn) noexcept
43	2632	: rn_(r0, rn...)
44		{
45	2632	}
46
47		private:
48
49		detail::tuple<R0, Rn...> rn_;
50		};
51		} // implementation_defined
52
53		/** Match one of a set of rules
54
55		Each specified rule is tried in sequence.
56		When the first match occurs, the result
57		is stored and returned in the variant. If
58		no match occurs, an error is returned.
59
60		@param r0 The first rule to match
61		@param rn A list of one or more rules to match
62		@return The variant rule
63
64		@par Value Type
65		@code
66		using value_type = variant< typename Rules::value_type... >;
67		@endcode
68
69		@par Example
70		Rules are used with the function @ref parse.
71		@code
72		// request-target = origin-form
73		// / absolute-form
74		// / authority-form
75		// / asterisk-form
76
77		system::result< variant< url_view, url_view, authority_view, core::string_view > > rv = grammar::parse(
78		"/index.html?width=full",
79		variant_rule(
80		origin_form_rule,
81		absolute_uri_rule,
82		authority_rule,
83		delim_rule('*') ) );
84		@endcode
85
86		@par BNF
87		@code
88		variant = rule1 / rule2 / rule3...
89		@endcode
90
91		@par Specification
92		@li <a href="https://datatracker.ietf.org/doc/html/rfc5234#section-3.2"
93		>3.2. Alternatives (rfc5234)</a>
94		@li <a href="https://datatracker.ietf.org/doc/html/rfc7230#section-5.3"
95		>5.3. Request Target (rfc7230)</a>
96
97		@see
98		@ref absolute_uri_rule,
99		@ref authority_rule,
100		@ref delim_rule,
101		@ref parse,
102		@ref origin_form_rule,
103		@ref url_view.
104		*/
105		template<
106		BOOST_URL_CONSTRAINT(Rule) R0,
107		BOOST_URL_CONSTRAINT(Rule)... Rn>
108		constexpr
109		auto
110		variant_rule(
111		R0 const& r0,
112		Rn const&... rn) noexcept ->
113		implementation_defined::variant_rule_t<R0, Rn...>;
114
115		} // grammar
116		} // urls
117		} // boost
118
119		#include <boost/url/grammar/impl/variant_rule.hpp>
120
121		#endif
122