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Make it possible to use non default constructible values in compositions

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This commit is contained in:
Denis Blank 2018-03-09 04:48:25 +01:00
parent 54385b5654
commit d59c0730b8
1 changed files with 24 additions and 5 deletions
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29
include/continuable/detail/composition-remapping.hpp
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@ -31,13 +31,14 @@
#ifndef CONTINUABLE_DETAIL_COMPOSITION_REMAPPING_HPP_INCLUDED
#define CONTINUABLE_DETAIL_COMPOSITION_REMAPPING_HPP_INCLUDED
#include <cassert>
#include <tuple>
#include <type_traits>
#include <utility>
#include <continuable/continuable-traverse.hpp>
#include <continuable/detail/base.hpp>
#include <continuable/detail/container-category.hpp>
#include <continuable/detail/flat-variant.hpp>
#include <continuable/detail/traits.hpp>
namespace cti {
@ -54,6 +55,24 @@ namespace composition {
/// - single async value -> single value
/// - multiple async value -> tuple of async values.
namespace remapping {
/// Guards a type to be default constructible,
/// and wraps it into an optional type if it isn't default constructible.
template <typename T>
using lazy_value_t = std::conditional_t<std::is_default_constructible<T>::value,
T, container::flat_variant<T>>;
template <typename T>
decltype(auto) unpack_lazy(T&& value) {
return std::forward<T>(value);
}
template <typename T>
T&& unpack_lazy(container::flat_variant<T>&& value) {
assert(value.template is<T>() &&
"The composition was finalized before all values were present!");
return std::move(value.template cast<T>());
}
template <typename Continuable>
class continuable_box;
template <typename Data>
@ -83,7 +102,7 @@ class continuable_box<
continuable_base<Data, hints::signature_hint_tag<First>>> {
continuable_base<Data, hints::signature_hint_tag<First>> continuable_;
First first_;
lazy_value_t<First> first_;
public:
explicit continuable_box(
@ -100,7 +119,7 @@ public:
}
auto unbox() && {
return std::move(first_);
return unpack_lazy(std::move(first_));
}
};
template <typename Data, typename First, typename Second, typename... Rest>
@ -109,7 +128,7 @@ class continuable_box<
continuable_base<Data, hints::signature_hint_tag<First, Second, Rest...>>
continuable_;
std::tuple<First, Second, Rest...> args_;
lazy_value_t<std::tuple<First, Second, Rest...>> args_;
public:
explicit continuable_box(
@ -130,7 +149,7 @@ public:
}
auto unbox() && {
return traits::unpack(std::move(args_), [](auto&&... args) {
return traits::unpack(unpack_lazy(std::move(args_)), [](auto&&... args) {
return spread_this(std::forward<decltype(args)>(args)...);
});
}