. /include/boost/url /grammar /optional_rule.hpp
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1   // 1   //
2   // Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com) 2   // Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
3   // Copyright (c) 2022 Alan de Freitas (alandefreitas@gmail.com) 3   // Copyright (c) 2022 Alan de Freitas (alandefreitas@gmail.com)
4   // 4   //
5   // Distributed under the Boost Software License, Version 1.0. (See accompanying 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) 6   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7   // 7   //
8   // Official repository: https://github.com/boostorg/url 8   // Official repository: https://github.com/boostorg/url
9   // 9   //
10   10  
11   #ifndef BOOST_URL_GRAMMAR_OPTIONAL_RULE_HPP 11   #ifndef BOOST_URL_GRAMMAR_OPTIONAL_RULE_HPP
12   #define BOOST_URL_GRAMMAR_OPTIONAL_RULE_HPP 12   #define BOOST_URL_GRAMMAR_OPTIONAL_RULE_HPP
13   13  
14   #include <boost/url/detail/config.hpp> 14   #include <boost/url/detail/config.hpp>
15   #include <boost/url/optional.hpp> 15   #include <boost/url/optional.hpp>
16   #include <boost/url/error_types.hpp> 16   #include <boost/url/error_types.hpp>
17   #include <boost/url/grammar/type_traits.hpp> 17   #include <boost/url/grammar/type_traits.hpp>
18   #include <boost/core/empty_value.hpp> 18   #include <boost/core/empty_value.hpp>
19   #include <boost/core/detail/static_assert.hpp> 19   #include <boost/core/detail/static_assert.hpp>
20   #include <boost/assert.hpp> 20   #include <boost/assert.hpp>
21   21  
22   namespace boost { 22   namespace boost {
23   namespace urls { 23   namespace urls {
24   namespace grammar { 24   namespace grammar {
25   25  
26   namespace implementation_defined { 26   namespace implementation_defined {
27   template<class Rule> 27   template<class Rule>
28   struct optional_rule_t 28   struct optional_rule_t
29   : private empty_value<Rule> 29   : private empty_value<Rule>
30   { 30   {
31   using value_type = boost::optional< 31   using value_type = boost::optional<
32   typename Rule::value_type>; 32   typename Rule::value_type>;
33   33  
34   BOOST_URL_CXX14_CONSTEXPR 34   BOOST_URL_CXX14_CONSTEXPR
35   system::result<value_type> 35   system::result<value_type>
36   parse( 36   parse(
37   char const*& it, 37   char const*& it,
38   char const* end) const; 38   char const* end) const;
39   39  
40   constexpr 40   constexpr
HITCBC 41   6730 optional_rule_t( 41   6730 optional_rule_t(
42   Rule const& r) noexcept 42   Rule const& r) noexcept
43   : empty_value<Rule>( 43   : empty_value<Rule>(
44   empty_init, 44   empty_init,
HITCBC 45   6730 r) 45   6730 r)
46   { 46   {
HITCBC 47   6730 } 47   6730 }
48   }; 48   };
49   } // implementation_defined 49   } // implementation_defined
50   50  
51   /** Match a rule, or the empty string 51   /** Match a rule, or the empty string
52   52  
53   Optional BNF elements are denoted with 53   Optional BNF elements are denoted with
54   square brackets. If the specified rule 54   square brackets. If the specified rule
55   returns any error it is treated as if 55   returns any error it is treated as if
56   the rule did not match. 56   the rule did not match.
57   57  
58   @par Value Type 58   @par Value Type
59   @code 59   @code
60   using value_type = optional< typename Rule::value_type >; 60   using value_type = optional< typename Rule::value_type >;
61   @endcode 61   @endcode
62   62  
63   @par Example 63   @par Example
64   Rules are used with the function @ref grammar::parse. 64   Rules are used with the function @ref grammar::parse.
65   @code 65   @code
66   system::result< optional< core::string_view > > rv = parse( "", optional_rule( token_rule( alpha_chars ) ) ); 66   system::result< optional< core::string_view > > rv = parse( "", optional_rule( token_rule( alpha_chars ) ) );
67   @endcode 67   @endcode
68   68  
69   @par BNF 69   @par BNF
70   @code 70   @code
71   optional = [ rule ] 71   optional = [ rule ]
72   @endcode 72   @endcode
73   73  
74   @par Specification 74   @par Specification
75   @li <a href="https://datatracker.ietf.org/doc/html/rfc5234#section-3.8" 75   @li <a href="https://datatracker.ietf.org/doc/html/rfc5234#section-3.8"
76   >3.8. Optional Sequence (rfc5234)</a> 76   >3.8. Optional Sequence (rfc5234)</a>
77   77  
78   @param r The rule to match 78   @param r The rule to match
79   @return The adapted rule 79   @return The adapted rule
80   80  
81   @see 81   @see
82   @ref alpha_chars, 82   @ref alpha_chars,
83   @ref parse, 83   @ref parse,
84   @ref optional, 84   @ref optional,
85   @ref token_rule. 85   @ref token_rule.
86   */ 86   */
87   template<BOOST_URL_CONSTRAINT(Rule) R> 87   template<BOOST_URL_CONSTRAINT(Rule) R>
88   auto 88   auto
89   constexpr 89   constexpr
HITCBC 90   6730 optional_rule( 90   6730 optional_rule(
91   R const& r) -> 91   R const& r) ->
92   implementation_defined::optional_rule_t<R> 92   implementation_defined::optional_rule_t<R>
93   { 93   {
94   BOOST_CORE_STATIC_ASSERT(grammar::is_rule<R>::value); 94   BOOST_CORE_STATIC_ASSERT(grammar::is_rule<R>::value);
HITCBC 95   6730 return { r }; 95   6730 return { r };
96   } 96   }
97   97  
98   } // grammar 98   } // grammar
99   } // urls 99   } // urls
100   } // boost 100   } // boost
101   101  
102   #include <boost/url/grammar/impl/optional_rule.hpp> 102   #include <boost/url/grammar/impl/optional_rule.hpp>
103   103  
104   #endif 104   #endif