Query the current value of the mapping property.

static constexpr execution::mapping_t query(
    execution::mapping_t );

Do not call this function directly. It is intended for use with the query customisation point.

For example:

boost::asio::system_executor ex;
if (boost::asio::query(ex, boost::asio::execution::mapping)
      == boost::asio::execution::mapping.thread)
  ...