robot/include/boost/url/grammar/tuple_rule.hpp

//
// Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// Official repository: https://github.com/boostorg/url
//

#ifndef BOOST_URL_GRAMMAR_TUPLE_RULE_HPP
#define BOOST_URL_GRAMMAR_TUPLE_RULE_HPP

#include <boost/url/detail/config.hpp>
#include <boost/url/error_types.hpp>
#include <boost/url/grammar/error.hpp>
#include <boost/url/grammar/detail/tuple.hpp>
#include <boost/mp11/algorithm.hpp>
#include <boost/core/empty_value.hpp>
#include <tuple>

namespace boost {
namespace urls {
namespace grammar {

/** Match a series of rules in order

    This matches a series of rules in the
    order specified. Upon success the input
    is adjusted to point to the first
    unconsumed character. There is no
    implicit specification of linear white
    space between each rule.

    @par Value Type
    @code
    using value_type = __see_below__;
    @endcode

    The sequence rule usually returns a
    `std::tuple` containing the the `value_type`
    of each corresponding rule in the sequence,
    except that `void` values are removed.
    However, if there is exactly one non-void
    value type `T`, then the sequence rule
    returns `system::result<T>` instead of
    `system::result<tuple<...>>`.

    @par Example
    Rules are used with the function @ref parse.
    @code
    system::result< std::tuple< unsigned char, unsigned char, unsigned char, unsigned char > > rv =
        parse( "192.168.0.1", 
            tuple_rule(
                dec_octet_rule,
                squelch( delim_rule('.') ),
                dec_octet_rule,
                squelch( delim_rule('.') ),
                dec_octet_rule,
                squelch( delim_rule('.') ),
                dec_octet_rule ) );
    @endcode

    @par BNF
    @code
    sequence     = rule1 rule2 rule3...
    @endcode

    @par Specification
    @li <a href="https://datatracker.ietf.org/doc/html/rfc5234#section-3.1"
        >3.1.  Concatenation (rfc5234)</a>

    @param rn A list of one or more rules to match

    @see
        @ref dec_octet_rule,
        @ref delim_rule,
        @ref parse,
        @ref squelch.
*/
#ifdef BOOST_URL_DOCS
template<class... Rules>
constexpr
__implementation_defined__
tuple_rule( Rules... rn ) noexcept;
#else
template<
    class R0,
    class... Rn>
class tuple_rule_t
    : empty_value<
        detail::tuple<R0, Rn...>>
{
    using T = mp11::mp_remove<
        std::tuple<
            typename R0::value_type,
            typename Rn::value_type...>,
        void>;
    static constexpr bool IsList =
        mp11::mp_size<T>::value != 1;

public:
    using value_type =
        mp11::mp_eval_if_c<IsList,
            T, mp11::mp_first, T>;

    template<
        class R0_,
        class... Rn_>
    friend
    constexpr
    auto
    tuple_rule(
        R0_ const& r0,
        Rn_ const&... rn) noexcept ->
            tuple_rule_t<R0_, Rn_...>;

    system::result<value_type>
    parse(
        char const*& it,
        char const* end) const;

private:
    constexpr
    tuple_rule_t(
        R0 const& r0,
        Rn const&... rn) noexcept
        : empty_value<
            detail::tuple<R0, Rn...>>(
                empty_init,
                r0, rn...)
    {
    }
};

template<
    class R0,
    class... Rn>
constexpr
auto
tuple_rule(
    R0 const& r0,
    Rn const&... rn) noexcept ->
        tuple_rule_t<
            R0, Rn...>
{
    return { r0, rn... };
}
#endif

#ifndef BOOST_URL_DOCS
namespace detail {

template<class Rule>
struct squelch_rule_t
    : empty_value<Rule>
{
    using value_type = void;

    constexpr
    squelch_rule_t(
        Rule const& r) noexcept
        : empty_value<Rule>(
            empty_init, r)
    {
    }

    system::result<value_type>
    parse(
        char const*& it,
        char const* end) const
    {
        auto rv = this->get().parse(it, end);
        if(rv.error())
            return rv.error();
        return {}; // void
    }
};

} // detail
#endif

/** Squelch the value of a rule

    This function returns a new rule which
    matches the specified rule, and converts
    its value type to `void`. This is useful
    for matching delimiters in a grammar,
    where the value for the delimiter is not
    needed.

    @par Value Type
    @code
    using value_type = void;
    @endcode

    @par Example 1
    With `squelch`:
    @code
    system::result< std::tuple< decode_view, core::string_view > > rv = parse(
        "www.example.com:443",
        tuple_rule(
            pct_encoded_rule(unreserved_chars + '-' + '.'),
            squelch( delim_rule( ':' ) ),
            token_rule( digit_chars ) ) );
    @endcode

    @par Example 2
    Without `squelch`:
    @code
    system::result< std::tuple< decode_view, core::string_view, core::string_view > > rv = parse(
        "www.example.com:443",
        tuple_rule(
            pct_encoded_rule(unreserved_chars + '-' + '.'),
            delim_rule( ':' ),
            token_rule( digit_chars ) ) );
    @endcode

    @param r The rule to squelch

    @see
        @ref delim_rule,
        @ref digit_chars,
        @ref parse,
        @ref tuple_rule,
        @ref token_rule,
        @ref decode_view,
        @ref pct_encoded_rule,
        @ref unreserved_chars.
*/
template<class Rule>
constexpr
#ifdef BOOST_URL_DOCS
__implementation_defined__
#else
detail::squelch_rule_t<Rule>
#endif
squelch( Rule const& r ) noexcept
{
    return { r };
}

} // grammar
} // urls
} // boost

#include <boost/url/grammar/impl/tuple_rule.hpp>

#endif