New class for return values of interface methods.

[randaz81]

This new class can be used in all interface methods to provide extra info about the success/failure of the method.
In this example:
bool getTemperature(int m, double* val) override;
becomes:
yarp::os::yarp_ret_value getTemperature(int m, double* val) override;
So the user can distinguish if a failure is due to missing implementation/internal error/communication error etc.
The class is also automatically converted to bool when tested by conditions.

Extra Notes:

• No need to change the user application code.
• Only devices (e.g. xxxmotioncontrol) must be updated.
• In this example, the error code is not actually propagated through the network (i.e. from the nws to the nwc).

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would update the release notes by adding a file in doc/release/<target_branch>, based on your changes.

[traversaro]

As we typically use CamelCase names for classes, and given this is return value is device-specific, could we call this type yarp::os::DeviceReturnValue ? Or perhaps we can move it to yarp::dev, unless there is some reason to keep it on yarp::os?

[randaz81]

As we typically use CamelCase names for classes, and given this is return value is device-specific, could we call this type yarp::os::DeviceReturnValue ? Or perhaps we can move it to yarp::dev, unless there is some reason to keep it on yarp::os?

Still not sure about the class name, but I like the idea of moving it to yarp::dev!

[PeterBowman]

Typo: "uninitialized".

Suggestion: isn't the "return_value_" prefix a bit verbose? I'm also thinking of an overload to LogStream so that this would be possible:

double val;
auto ret = iMotor->getTemperature(0, &val);
yInfo() << ret; // prints "ok", "error_generic" "error_not_implemented" and so on

[randaz81]

That's a nice idea! Just give me a little more time before proceeding since we need to edit a few things more before.