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Initiate an asynchronous wait for the group of operations.
template< typename CancellationCondition, typename CompletionToken> DEDUCED async_wait( CancellationCondition cancellation_condition, CompletionToken && token);
Launches the group and asynchronously waits for completion.
                A function object, called on completion of an operation within the
                group, that is used to determine whether to cancel the remaining
                operations. The function object is passed the arguments of the completed
                operation's handler. To trigger cancellation of the remaining operations,
                it must return a cancellation_type value
                other than asio::cancellation_type::none.
              
                A completion
                token whose signature is comprised of a std::vector<std::size_t, Allocator> indicating the completion order
                of the operations, followed by a vector for each of the completion
                signature's arguments.
              
          The library provides the following cancellation_condition
          types: