Line data    Source code

       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_OPTIONAL_RULE_HPP
      11              : #define BOOST_URL_GRAMMAR_OPTIONAL_RULE_HPP
      12              : 
      13              : #include <boost/url/detail/config.hpp>
      14              : #include <boost/url/optional.hpp>
      15              : #include <boost/url/error_types.hpp>
      16              : #include <boost/url/grammar/type_traits.hpp>
      17              : #include <boost/core/empty_value.hpp>
      18              : #include <boost/assert.hpp>
      19              : 
      20              : namespace boost {
      21              : namespace urls {
      22              : namespace grammar {
      23              : 
      24              : namespace implementation_defined {
      25              : template<class Rule>
      26              : struct optional_rule_t
      27              :     : private empty_value<Rule>
      28              : {
      29              :     using value_type = boost::optional<
      30              :         typename Rule::value_type>;
      31              : 
      32              :     system::result<value_type>
      33              :     parse(
      34              :         char const*& it,
      35              :         char const* end) const;
      36              : 
      37              :     constexpr
      38         1967 :     optional_rule_t(
      39              :         Rule const& r) noexcept
      40              :         : empty_value<Rule>(
      41              :             empty_init,
      42         1967 :             r)
      43              :     {
      44         1967 :     }
      45              : };
      46              : } // implementation_defined
      47              : 
      48              : /** Match a rule, or the empty string
      49              : 
      50              :     Optional BNF elements are denoted with
      51              :     square brackets. If the specified rule
      52              :     returns any error it is treated as if
      53              :     the rule did not match.
      54              : 
      55              :     @par Value Type
      56              :     @code
      57              :     using value_type = optional< typename Rule::value_type >;
      58              :     @endcode
      59              : 
      60              :     @par Example
      61              :     Rules are used with the function @ref grammar::parse.
      62              :     @code
      63              :     system::result< optional< core::string_view > > rv = parse( "", optional_rule( token_rule( alpha_chars ) ) );
      64              :     @endcode
      65              : 
      66              :     @par BNF
      67              :     @code
      68              :     optional     = [ rule ]
      69              :     @endcode
      70              : 
      71              :     @par Specification
      72              :     @li <a href="https://datatracker.ietf.org/doc/html/rfc5234#section-3.8"
      73              :         >3.8.  Optional Sequence (rfc5234)</a>
      74              : 
      75              :     @param r The rule to match
      76              : 
      77              :     @see
      78              :         @ref alpha_chars,
      79              :         @ref parse,
      80              :         @ref optional,
      81              :         @ref token_rule.
      82              : */
      83              : template<BOOST_URL_CONSTRAINT(Rule) R>
      84              : auto
      85              : constexpr
      86         1967 : optional_rule(
      87              :     R const& r) ->
      88              :         implementation_defined::optional_rule_t<R>
      89              : {
      90              :     BOOST_STATIC_ASSERT(grammar::is_rule<R>::value);
      91         1967 :     return { r };
      92              : }
      93              : 
      94              : } // grammar
      95              : } // urls
      96              : } // boost
      97              : 
      98              : #include <boost/url/grammar/impl/optional_rule.hpp>
      99              : 
     100              : #endif