A wait token is a completion token for completion signature void(error_code).

Examples

A free function as a wait token:

void wait_handler(
    const asio::error_code& ec)
{
  ...
}

A wait token function object:

struct wait_handler
{
  ...
  void operator()(
      const asio::error_code& ec)
  {
    ...
  }
  ...
};

A lambda as a wait token:

socket.async_wait(...,
    [](const asio::error_code& ec)
    {
      ...
    });

A non-static class member function adapted to a wait token using std::bind():

void my_class::wait_handler(
    const asio::error_code& ec)
{
  ...
}
...
socket.async_wait(...,
    std::bind(&my_class::wait_handler,
      this, std::placeholders::_1));

A non-static class member function adapted to a wait token using boost::bind():

void my_class::wait_handler(
    const asio::error_code& ec)
{
  ...
}
...
socket.async_wait(...,
    boost::bind(&my_class::wait_handler,
      this, asio::placeholders::error));

Using use_future as a wait token:

std::future<void> f = socket.async_wait(..., asio::use_future);
...
try
{
  f.get();
}
catch (const system_error& e)
{
  ...
}

Using use_awaitable as a wait token:

asio::awaitable<void> my_coroutine()
{
  try
  {
    ...
    co_await socket.async_wait(..., asio::use_awaitable);
    ...
  }
  catch (const system_error& e)
  {
    ...
  }
}