113 lines
2.3 KiB
C++
113 lines
2.3 KiB
C++
//
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// Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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// Official repository: https://github.com/boostorg/url
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//
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#ifndef BOOST_URL_GRAMMAR_OPTIONAL_RULE_HPP
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#define BOOST_URL_GRAMMAR_OPTIONAL_RULE_HPP
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#include <boost/url/detail/config.hpp>
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#include <boost/url/optional.hpp>
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#include <boost/url/error_types.hpp>
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#include <boost/core/empty_value.hpp>
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#include <boost/assert.hpp>
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namespace boost {
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namespace urls {
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namespace grammar {
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/** Match a rule, or the empty string
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Optional BNF elements are denoted with
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square brackets. If the specified rule
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returns any error it is treated as if
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the rule did not match.
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@par Value Type
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@code
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using value_type = optional< typename Rule::value_type >;
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@endcode
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@par Example
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Rules are used with the function @ref grammar::parse.
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@code
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result< optional< string_view > > rv = parse( "", optional_rule( token_rule( alpha_chars ) ) );
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@endcode
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@par BNF
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@code
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optional = [ rule ]
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@endcode
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@par Specification
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@li <a href="https://datatracker.ietf.org/doc/html/rfc5234#section-3.8"
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>3.8. Optional Sequence (rfc5234)</a>
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@param r The rule to match
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@see
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@ref alpha_chars,
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@ref parse,
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@ref optional,
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@ref token_rule.
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*/
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#ifdef BOOST_URL_DOCS
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template<class Rule>
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constexpr
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__implementation_defined__
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optional_rule( Rule r ) noexcept;
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#else
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template<class Rule>
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struct optional_rule_t
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: private empty_value<Rule>
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{
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using value_type = optional<
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typename Rule::value_type>;
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result<value_type>
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parse(
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char const*& it,
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char const* end) const;
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template<class R_>
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friend
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constexpr
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auto
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optional_rule(
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R_ const& r) ->
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optional_rule_t<R_>;
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private:
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constexpr
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optional_rule_t(
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Rule const& r) noexcept
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: empty_value<Rule>(
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empty_init,
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r)
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{
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}
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};
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template<class Rule>
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auto
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constexpr
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optional_rule(
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Rule const& r) ->
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optional_rule_t<Rule>
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{
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return { r };
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}
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#endif
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} // grammar
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} // urls
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} // boost
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#include <boost/url/grammar/impl/optional_rule.hpp>
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#endif
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