A forward range of buffer sequences, one per datagram to send. Although the range object may be copied as necessary, ownership of the underlying memory blocks is retained by the caller, which must guarantee that they remain valid until the completion handler is called.

A forward range of destination endpoints, one per datagram. Although the range object may be copied as necessary, ownership of any endpoints to which the range yields references is retained by the caller, which must guarantee that they remain valid until the completion handler is called. Copies will be made of endpoints yielded by value as required.

The completion token that will be used to produce a completion handler, which will be called when the send completes. Potential completion tokens include use_future, use_awaitable, yield_context, or a function object with the correct completion signature. The function signature of the completion handler must be:

void handler(
  const boost::system::error_code& error, // Result of operation.
  std::size_t messages_transferred // Number of datagrams sent.
);

Regardless of whether the asynchronous operation completes immediately or not, the completion handler will not be invoked from within this function. On immediate completion, invocation of the handler will be performed in a manner equivalent to using async_immediate.