Line data    Source code

       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_OPTIONAL_RULE_HPP
      12              : #define BOOST_URL_GRAMMAR_OPTIONAL_RULE_HPP
      13              : 
      14              : #include <boost/url/detail/config.hpp>
      15              : #include <boost/url/optional.hpp>
      16              : #include <boost/url/error_types.hpp>
      17              : #include <boost/url/grammar/type_traits.hpp>
      18              : #include <boost/core/empty_value.hpp>
      19              : #include <boost/core/detail/static_assert.hpp>
      20              : #include <boost/assert.hpp>
      21              : 
      22              : namespace boost {
      23              : namespace urls {
      24              : namespace grammar {
      25              : 
      26              : namespace implementation_defined {
      27              : template<class Rule>
      28              : struct optional_rule_t
      29              :     : private empty_value<Rule>
      30              : {
      31              :     using value_type = boost::optional<
      32              :         typename Rule::value_type>;
      33              : 
      34              :     BOOST_URL_CXX14_CONSTEXPR
      35              :     system::result<value_type>
      36              :     parse(
      37              :         char const*& it,
      38              :         char const* end) const;
      39              : 
      40              :     constexpr
      41         2137 :     optional_rule_t(
      42              :         Rule const& r) noexcept
      43              :         : empty_value<Rule>(
      44              :             empty_init,
      45         2137 :             r)
      46              :     {
      47         2137 :     }
      48              : };
      49              : } // implementation_defined
      50              : 
      51              : /** Match a rule, or the empty string
      52              : 
      53              :     Optional BNF elements are denoted with
      54              :     square brackets. If the specified rule
      55              :     returns any error it is treated as if
      56              :     the rule did not match.
      57              : 
      58              :     @par Value Type
      59              :     @code
      60              :     using value_type = optional< typename Rule::value_type >;
      61              :     @endcode
      62              : 
      63              :     @par Example
      64              :     Rules are used with the function @ref grammar::parse.
      65              :     @code
      66              :     system::result< optional< core::string_view > > rv = parse( "", optional_rule( token_rule( alpha_chars ) ) );
      67              :     @endcode
      68              : 
      69              :     @par BNF
      70              :     @code
      71              :     optional     = [ rule ]
      72              :     @endcode
      73              : 
      74              :     @par Specification
      75              :     @li <a href="https://datatracker.ietf.org/doc/html/rfc5234#section-3.8"
      76              :         >3.8.  Optional Sequence (rfc5234)</a>
      77              : 
      78              :     @param r The rule to match
      79              :     @return The adapted rule
      80              : 
      81              :     @see
      82              :         @ref alpha_chars,
      83              :         @ref parse,
      84              :         @ref optional,
      85              :         @ref token_rule.
      86              : */
      87              : template<BOOST_URL_CONSTRAINT(Rule) R>
      88              : auto
      89              : constexpr
      90         2137 : optional_rule(
      91              :     R const& r) ->
      92              :         implementation_defined::optional_rule_t<R>
      93              : {
      94              :     BOOST_CORE_STATIC_ASSERT(grammar::is_rule<R>::value);
      95         2137 :     return { r };
      96              : }
      97              : 
      98              : } // grammar
      99              : } // urls
     100              : } // boost
     101              : 
     102              : #include <boost/url/grammar/impl/optional_rule.hpp>
     103              : 
     104              : #endif