tdesktop/Telegram/SourceFiles/rpl/variable.h

157 lines
3.8 KiB
C++

/*
This file is part of Telegram Desktop,
the official desktop application for the Telegram messaging service.
For license and copyright information please follow this link:
https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
*/
#pragma once
#include <rpl/producer.h>
#include <rpl/event_stream.h>
namespace mapbox {
namespace util {
template <typename ...Types>
class variant;
} // namespace util
} // namespace mapbox
namespace rpl {
namespace details {
template <typename A, typename B>
struct supports_equality_compare {
template <typename U, typename V>
static auto test(const U *u, const V *v)
-> decltype(*u == *v, true_t());
static false_t test(...);
static constexpr bool value
= (sizeof(test((const A*)nullptr, (const B*)nullptr))
== sizeof(true_t));
};
// Fix for MSVC expression SFINAE.
// It still doesn't work! :(
//
//template <typename Type1, typename ...Types1>
//struct supports_equality_compare<
// mapbox::util::variant<Type1, Types1...>,
// mapbox::util::variant<Type1, Types1...>> {
// static constexpr bool value
// = (supports_equality_compare<Type1, Type1>::value
// && supports_equality_compare<
// mapbox::util::variant<Types1...>,
// mapbox::util::variant<Types1...>>::value);
//
//};
//template <typename Type>
//struct supports_equality_compare<
// mapbox::util::variant<Type>,
// mapbox::util::variant<Type>> {
// static constexpr bool value = supports_equality_compare<Type, Type>::value;
//
//};
template <typename A, typename B>
constexpr bool supports_equality_compare_v
= supports_equality_compare<std::decay_t<A>, std::decay_t<B>>::value;
} // namespace details
template <typename Type>
class variable final {
public:
variable() : _data{} {
}
variable(variable &&other) : _data(std::move(other._data)) {
}
variable &operator=(variable &&other) {
return (*this = std::move(other._data));
}
template <
typename OtherType,
typename = std::enable_if_t<
std::is_constructible_v<Type, OtherType&&>>>
variable(OtherType &&data) : _data(std::forward<OtherType>(data)) {
}
template <
typename OtherType,
typename = std::enable_if_t<
std::is_assignable_v<Type&, OtherType&&>>>
variable &operator=(OtherType &&data) {
_lifetime.destroy();
return assign(std::forward<OtherType>(data));
}
template <
typename OtherType,
typename Error,
typename Generator,
typename = std::enable_if_t<
std::is_assignable_v<Type&, OtherType>>>
variable(producer<OtherType, Error, Generator> &&stream) {
std::move(stream)
| start_with_next([this](auto &&data) {
assign(std::forward<decltype(data)>(data));
}, _lifetime);
}
template <
typename OtherType,
typename Error,
typename Generator,
typename = std::enable_if_t<
std::is_assignable_v<Type&, OtherType>>>
variable &operator=(
producer<OtherType, Error, Generator> &&stream) {
_lifetime.destroy();
std::move(stream)
| start_with_next([this](auto &&data) {
assign(std::forward<decltype(data)>(data));
}, _lifetime);
}
Type current() const {
return _data;
}
auto value() const {
return _changes.events_starting_with_copy(_data);
}
auto changes() const {
return _changes.events();
}
private:
template <typename OtherType>
variable &assign(OtherType &&data) {
if constexpr (details::supports_equality_compare_v<Type, OtherType>) {
if (!(_data == data)) {
_data = std::forward<OtherType>(data);
_changes.fire_copy(_data);
}
} else if constexpr (details::supports_equality_compare_v<Type, Type>) {
auto old = std::move(_data);
_data = std::forward<OtherType>(data);
if (!(_data == old)) {
_changes.fire_copy(_data);
}
} else {
_data = std::forward<OtherType>(data);
_changes.fire_copy(_data);
}
return *this;
}
Type _data;
event_stream<Type> _changes;
lifetime _lifetime;
};
} // namespace rpl