get_all.hpp

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#pragma once
 
 
#include <type_traits>
#include <vector>
 
#include <userver/engine/wait_all_checked.hpp>
#include <userver/utils/meta.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace engine {
 
template <typename... Tasks>
auto GetAll(Tasks&... tasks);
 
namespace impl {
 
template <typename Container>
auto GetAllResultsFromContainer(Container& tasks) {
  using Result = decltype(std::begin(tasks)->Get());
 
  if constexpr (std::is_void_v<Result>) {
    for (auto& task : tasks) {
      task.Get();
    }
    return;
  } else {
    std::vector<Result> results;
    results.reserve(std::size(tasks));
    for (auto& task : tasks) {
      results.push_back(task.Get());
    }
    return results;
  }
}
 
template <typename... Tasks>
auto GetAllResultsFromTasks(Tasks&... tasks) {
  using Result = decltype((void(), ..., tasks.Get()));
 
  if constexpr (std::is_void_v<Result>) {
    static_assert((true && ... && std::is_void_v<decltype(tasks.Get())>));
    (tasks.Get(), ...);
    return;
  } else {
    std::vector<Result> results;
    results.reserve(sizeof...(tasks));
    (results.push_back(tasks.Get()), ...);
    return results;
  }
}
 
}  // namespace impl
 
template <typename... Tasks>
auto GetAll(Tasks&... tasks) {
  engine::WaitAllChecked(tasks...);
  if constexpr (meta::impl::IsSingleRange<Tasks...>()) {
    return impl::GetAllResultsFromContainer(tasks...);
  } else {
    return impl::GetAllResultsFromTasks(tasks...);
  }
}
 
}  // namespace engine
 
USERVER_NAMESPACE_END