Multiple Return Values

Multiple Return Values

dbus-cxx has support for multiple return values from functions. In order to utilize this, you must use the DBus::MultipleReturn class. This class is essentially a wrapper around std::tuple, but provides the types needed by the library to properly handle the logic with multiple return values.

Because this is basically a wrapper around std::tuple, in order to get the values is a two step process:

1. Get the tuple
2. Use std::get in order to get the values

Example:

DBus::MultipleReturn<int32_t, int32_t, std::string, std::vector<int>> val;
 
// Call the method that returns multiple values
// This must have been previously created, and would look something like:
// std::shared_ptr<DBus::MethodProxy<DBus::MultipleReturn<int32_t, int32_t, std::string, std::vector<int>>()>> method_proxy;
// Notice how the return value is defined as a DBus::MultipleReturn, and there are no arguments to the method proxy
val = (*method_proxy)();
 
std::tuple<int32_t, int32_t, std::string, std::vector<int>> d = val.m_data;
 
std::get<0>(d);  // Get the first int32_t in our tuple d
std::get<1>(d);  // Get the second int32_t in our tuple d
std::get<2>(d);  // Get the std::string in our tuple d
// ... etc ...

Note that if you name arguments(using the DBus::MethodBase.set_arg_name() method), the earlier argument names are the return values. For example, if your multiple return has two arguments, set_arg_name(0, "name") and set_arg_name(1, "name") are the way to set the arguments. The remaining arg names are for parameters to the function.