use_resources.h

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#pragma once
 
#include "di/execution/algorithm/let_value_with.h"
#include "di/execution/concepts/sender.h"
#include "di/execution/interface/run.h"
#include "di/execution/sequence/first_value.h"
#include "di/execution/sequence/let_each.h"
#include "di/execution/sequence/zip.h"
#include "di/function/invoke.h"
#include "di/function/tag_invoke.h"
#include "di/meta/util.h"
#include "di/util/move.h"
 
namespace di::execution {
namespace use_resources_ns {
    struct Function {
        template<concepts::MovableValue Fun, concepts::MovableValue... Deferred>
        requires(concepts::AsyncResource<meta::InvokeResult<meta::Decay<Deferred> &&>> && ...)
        auto operator()(Fun&& function, Deferred&&... deferred) const {
            if constexpr (concepts::TagInvocable<Function, Fun, Deferred...>) {
                static_assert(concepts::Sender<meta::TagInvokeResult<Function, Fun, Deferred...>>,
                              "use_resources() customizations must return a Sender.");
                return function::tag_invoke(*this, util::forward<Fun>(function), util::forward<Deferred>(deferred)...);
            } else {
                return execution::let_value_with(
                    [function = util::forward<Fun>(function)](auto&... resources) {
                        return first_value(zip(run(resources)...) | let_value_each(util::move(function)));
                    },
                    util::forward<Deferred>(deferred)...);
            }
        }
    };
}

constexpr inline auto use_resources = use_resources_ns::Function {};
}