c7a814fd5c
The operator== of enum_option<> (which we use to hold multi-valued Scylla options) makes it easy to compare to another enum_option wrapper, but ugly to compare the actual value held. So this patch adds a nicer way to compare the value held. Signed-off-by: Nadav Har'El <nyh@scylladb.com> Message-Id: <20210511120222.1167686-1-nyh@scylladb.com>
127 lines
4.2 KiB
C++
127 lines
4.2 KiB
C++
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/*
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* Copyright (C) 2015 ScyllaDB
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*/
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/*
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* This file is part of Scylla.
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*
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* Scylla is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Scylla is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
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*/
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// TODO: upstream this to Boost.
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#pragma once
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#include <boost/program_options/errors.hpp>
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#include <iostream>
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#include <sstream>
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#include <type_traits>
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template<typename T>
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concept HasMapInterface = requires(T t) {
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typename std::remove_reference<T>::type::mapped_type;
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typename std::remove_reference<T>::type::key_type;
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typename std::remove_reference<T>::type::value_type;
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t.find(typename std::remove_reference<T>::type::key_type());
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t.begin();
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t.end();
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t.cbegin();
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t.cend();
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};
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/// A Boost program option holding an enum value.
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///
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/// The options parser will parse enum values with the help of the Mapper class, which provides a mapping
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/// between some parsable form (eg, string) and the enum value. For example, it may map the word "January" to
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/// the enum value JANUARY.
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///
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/// Mapper must have a static method `map()` that returns a map from a streamable key type (eg, string) to the
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/// enum in question. In fact, enum_option knows which enum it represents only by referencing
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/// Mapper::map().mapped_type.
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///
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/// \note one enum_option holds only one enum value. When multiple choices are allowed, use
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/// vector<enum_option>.
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///
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/// Example:
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///
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/// struct Type {
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/// enum ty { a1, a2, b1 };
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/// static unordered_map<string, ty> map();
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/// };
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/// unordered_map<string, Type::ty> Type::map() {
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/// return {{"a1", Type::a1}, {"a2", Type::a2}, {"b1", Type::b1}};
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/// }
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/// int main(int ac, char* av[]) {
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/// namespace po = boost::program_options;
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/// po::options_description desc("Allowed options");
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/// desc.add_options()
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/// ("val", po::value<enum_option<Type>>(), "Single Type")
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/// ("vec", po::value<vector<enum_option<Type>>>()->multitoken(), "Type vector");
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/// }
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template<typename Mapper>
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requires HasMapInterface<decltype(Mapper::map())>
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class enum_option {
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using map_t = typename std::remove_reference<decltype(Mapper::map())>::type;
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typename map_t::mapped_type _value;
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map_t _map;
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public:
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// For smooth conversion from enum values:
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enum_option(const typename map_t::mapped_type& v) : _value(v), _map(Mapper::map()) {}
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// So values can be default-constructed before streaming into them:
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enum_option() : _map(Mapper::map()) {}
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bool operator==(const enum_option<Mapper>& that) const {
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return _value == that._value;
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}
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bool operator==(typename map_t::mapped_type value) const {
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return _value == value;
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}
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// For program_options parser:
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friend std::istream& operator>>(std::istream& s, enum_option<Mapper>& opt) {
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typename map_t::key_type key;
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s >> key;
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const auto found = opt._map.find(key);
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if (found == opt._map.end()) {
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std::string text;
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if (s.rdstate() & s.failbit) {
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// key wasn't read successfully.
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s >> text;
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} else {
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// Turn key into text.
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std::ostringstream temp;
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temp << key;
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text = temp.str();
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}
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throw boost::program_options::invalid_option_value(text);
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}
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opt._value = found->second;
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return s;
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}
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// For various printers and formatters:
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friend std::ostream& operator<<(std::ostream& s, const enum_option<Mapper>& opt) {
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auto found = find_if(opt._map.cbegin(), opt._map.cend(),
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[&opt](const typename map_t::value_type& e) { return e.second == opt._value; });
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if (found == opt._map.cend()) {
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return s << "?unknown";
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} else {
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return s << found->first;
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}
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}
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};
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