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Question: Type-safety of the blackboard values #569
Description
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.
Activity
facontidavide commentedon May 26, 2023
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:
std::anywould complain if you try to castuint16_ttoint32_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
getInputandsetOutputinterfaces (as you should).You can not connect a
OutputPort<float>toInputPort<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 commentedon May 26, 2023
@facontidavide Great, thanks a lot for clearing that up.