Question: Type-safety of the blackboard values

[MithunKinarullathil]

Hi,

From the documentation I learned that the values in the blackboard are type-safe. Further reading I saw this section

BehaviorTree.CPP supports automatically converting strings into common types, such as int, long, double, bool, NodeStatus, etc. User-defined types can be supported easily as well.

My doubt this: are the values in the blackboard always stored as strings? If so, is there a way to guarantee type safety?

eg: Image a key:value pair with std:int type and value 3. In another action node, later on in the tree, would I be able to save an std:float into the same key?

Thank you for your time.

[facontidavide]

great question!

BB storage

Storage is done with a variant of std::any. if you are unfamiliar with it, I strongly recommend you learn how that works.
std::any implements type erasure (store any type), but preserving the original object AND its type.

NOW, in addition to any, we do:

• small object optimization to prevent allocating memory in the heap if the object is 16 bytes or less.
• smart casting. For instance, a regular std::any would complain if you try to cast uint16_t to int32_t, but instead I check if there is any numberical error in the casting, and if there isn't, it is allowed.

But wait, there is more.

If you DO KNOW the type of a blackboard entry / port, we will automatically TRY to convert the string to that type.

Answer

I am assuming you will use the provided getInput and setOutput interfaces (as you should).

You can not connect a OutputPort<float> to InputPort<int> because they haven't the same type.

If everything works as intended, you should get an exception during the creation of the tree.

You can do, anyway getInput<float>() of an integer port, if that is not causing numerical cancellation.

[MithunKinarullathil]

@facontidavide Great, thanks a lot for clearing that up.