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107 lines
2.9 KiB
C++
107 lines
2.9 KiB
C++
// This file is part of Desktop App Toolkit,
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// a set of libraries for developing nice desktop applications.
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//
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// For license and copyright information please follow this link:
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// https://github.com/desktop-app/legal/blob/master/LEGAL
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//
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#pragma once
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#include <rpl/producer.h>
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#include "base/optional.h"
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namespace rpl {
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namespace details {
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class combine_previous_helper {
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public:
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template <typename Value, typename Error, typename Generator>
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auto operator()(
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producer<Value, Error, Generator> &&initial) const {
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return make_producer<std::tuple<Value, Value>, Error>([
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initial = std::move(initial)
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](const auto &consumer) mutable {
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auto previous = consumer.template make_state<
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std::optional<Value>
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>();
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return std::move(initial).start(
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[consumer, previous](auto &&value) {
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if (auto &exists = *previous) {
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auto &existing = *exists;
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auto next = std::make_tuple(
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std::move(existing),
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value);
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consumer.put_next(std::move(next));
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existing = std::forward<decltype(value)>(
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value);
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} else {
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*previous = std::forward<decltype(value)>(
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value);
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}
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}, [consumer](auto &&error) {
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consumer.put_error_forward(std::forward<decltype(error)>(error));
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}, [consumer] {
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consumer.put_done();
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});
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});
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}
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};
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template <typename DefaultValue>
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class combine_previous_with_default_helper {
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public:
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template <typename OtherValue>
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combine_previous_with_default_helper(OtherValue &&value)
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: _value(std::forward<OtherValue>(value)) {
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}
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template <typename Value, typename Error, typename Generator>
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auto operator()(producer<Value, Error, Generator> &&initial) {
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return make_producer<std::tuple<Value, Value>, Error>([
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initial = std::move(initial),
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value = Value(std::move(_value))
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](const auto &consumer) mutable {
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auto previous = consumer.template make_state<Value>(
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std::move(value));
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return std::move(initial).start(
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[consumer, previous](auto &&value) {
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auto &existing = *previous;
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auto next = std::make_tuple(
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std::move(existing),
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value);
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consumer.put_next(std::move(next));
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existing = std::forward<decltype(value)>(value);
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}, [consumer](auto &&error) {
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consumer.put_error_forward(std::forward<decltype(error)>(error));
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}, [consumer] {
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consumer.put_done();
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});
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});
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}
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private:
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DefaultValue _value;
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};
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template <typename DefaultValue>
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combine_previous_with_default_helper<std::decay_t<DefaultValue>>
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combine_previous_with_default(DefaultValue &&value) {
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return { std::forward<DefaultValue>(value) };
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}
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} // namespace details
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inline auto combine_previous()
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-> details::combine_previous_helper {
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return details::combine_previous_helper();
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}
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template <typename DefaultValue>
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inline auto combine_previous(DefaultValue &&value) {
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return details::combine_previous_with_default(
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std::forward<DefaultValue>(value));
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}
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} // namespace rpl
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