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// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.
#pragma once
/*! \file rx-switch_if_empty.hpp
\brief If the source Observable terminates without emitting any items, emits items from a backup Observable.
\tparam BackupSource the type of the backup observable.
\param t a backup observable that is used if the source observable is empty.
\return Observable that emits items from a backup observable if the source observable is empty.
\sample
\snippet switch_if_empty.cpp switch_if_empty sample
\snippet output.txt switch_if_empty sample
*/
#if !defined(RXCPP_OPERATORS_RX_SWITCH_IF_EMPTY_HPP)
#define RXCPP_OPERATORS_RX_SWITCH_IF_EMPTY_HPP
#include "../rx-includes.hpp"
namespace rxcpp {
namespace operators {
namespace detail {
template<class... AN>
struct switch_if_empty_invalid_arguments {};
template<class... AN>
struct switch_if_empty_invalid : public rxo::operator_base<switch_if_empty_invalid_arguments<AN...>> {
using type = observable<switch_if_empty_invalid_arguments<AN...>, switch_if_empty_invalid<AN...>>;
};
template<class... AN>
using switch_if_empty_invalid_t = typename switch_if_empty_invalid<AN...>::type;
template<class T, class BackupSource>
struct switch_if_empty
{
typedef rxu::decay_t<T> source_value_type;
typedef rxu::decay_t<BackupSource> backup_source_type;
backup_source_type backup;
switch_if_empty(backup_source_type b)
: backup(std::move(b))
{
}
template<class Subscriber>
struct switch_if_empty_observer
{
typedef switch_if_empty_observer<Subscriber> this_type;
typedef source_value_type value_type;
typedef rxu::decay_t<Subscriber> dest_type;
typedef observer<value_type, this_type> observer_type;
dest_type dest;
composite_subscription lifetime;
backup_source_type backup;
mutable bool is_empty;
switch_if_empty_observer(dest_type d, composite_subscription cs, backup_source_type b)
: dest(std::move(d))
, lifetime(std::move(cs))
, backup(std::move(b))
, is_empty(true)
{
dest.add(lifetime);
}
void on_next(source_value_type v) const {
is_empty = false;
dest.on_next(std::move(v));
}
void on_error(rxu::error_ptr e) const {
dest.on_error(std::move(e));
}
void on_completed() const {
if(!is_empty) {
dest.on_completed();
} else {
backup.subscribe(dest);
}
}
static subscriber<value_type, observer_type> make(dest_type d, backup_source_type b) {
auto cs = composite_subscription();
return make_subscriber<value_type>(cs, observer_type(this_type(std::move(d), cs, std::move(b))));
}
};
template<class Subscriber>
auto operator()(Subscriber dest) const
-> decltype(switch_if_empty_observer<Subscriber>::make(std::move(dest), std::move(backup))) {
return switch_if_empty_observer<Subscriber>::make(std::move(dest), std::move(backup));
}
};
}
/*! @copydoc rx-switch_if_empty.hpp
*/
template<class... AN>
auto switch_if_empty(AN&&... an)
-> operator_factory<switch_if_empty_tag, AN...> {
return operator_factory<switch_if_empty_tag, AN...>(std::make_tuple(std::forward<AN>(an)...));
}
/*! \brief If the source Observable terminates without emitting any items, emits a default item and completes.
\tparam Value the type of the value to emit.
\param v the default value to emit.
\return Observable that emits the specified default item if the source observable is empty.
\sample
\snippet default_if_empty.cpp default_if_empty sample
\snippet output.txt default_if_empty sample
*/
template<class... AN>
auto default_if_empty(AN&&... an)
-> operator_factory<default_if_empty_tag, AN...> {
return operator_factory<default_if_empty_tag, AN...>(std::make_tuple(std::forward<AN>(an)...));
}
}
template<>
struct member_overload<switch_if_empty_tag>
{
template<class Observable, class BackupSource,
class Enabled = rxu::enable_if_all_true_type_t<
all_observables<Observable, BackupSource>>,
class SourceValue = rxu::value_type_t<Observable>,
class SwitchIfEmpty = rxo::detail::switch_if_empty<SourceValue, rxu::decay_t<BackupSource>>>
static auto member(Observable&& o, BackupSource&& b)
-> decltype(o.template lift<SourceValue>(SwitchIfEmpty(std::forward<BackupSource>(b)))) {
return o.template lift<SourceValue>(SwitchIfEmpty(std::forward<BackupSource>(b)));
}
template<class... AN>
static operators::detail::switch_if_empty_invalid_t<AN...> member(AN...) {
std::terminate();
return {};
static_assert(sizeof...(AN) == 10000, "switch_if_empty takes (BackupSource)");
}
};
template<>
struct member_overload<default_if_empty_tag>
{
template<class Observable, class Value,
class Enabled = rxu::enable_if_all_true_type_t<
is_observable<Observable>>,
class SourceValue = rxu::value_type_t<Observable>,
class BackupSource = decltype(rxs::from(std::declval<SourceValue>())),
class DefaultIfEmpty = rxo::detail::switch_if_empty<SourceValue, BackupSource>>
static auto member(Observable&& o, Value v)
-> decltype(o.template lift<SourceValue>(DefaultIfEmpty(rxs::from(std::move(v))))) {
return o.template lift<SourceValue>(DefaultIfEmpty(rxs::from(std::move(v))));
}
template<class... AN>
static operators::detail::switch_if_empty_invalid_t<AN...> member(AN...) {
std::terminate();
return {};
static_assert(sizeof...(AN) == 10000, "default_if_empty takes (Value)");
}
};
}
#endif
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