Hi all, recently I have been working on supporting dynamic tags like “_itemCount”, “_curItem” and “_lastItem” in array elements.
In java I used ThreadLocals for this as it felt like a Java-Native way and it wouldn’t blow up the signatures of our Parser, Serializer and GetLengthInXYZ methods. Now when looking for something similar in Go, it seems in such cases Contexts are used. These are sort of like a HashMap wrapped with little util methods. In this HashMap you pass along values that are “in context” … if you change the context, a copy of the old context is created and then the updated/added values are updated/added to the HashMap. So, in an array I add the additional information to the existing one by: arrayCtx := spiContext.CreateArrayContext(ctx, int(_numItems), int(_curItem)) and then simply pass in the „arrayContext”. And for accessing it I simply for this: spiContext.GetLastItemFromContext(ctx) Admittedly I’m not a big fan of crating copies of the full context every time, I would prefer to be able to push to sort of a context stack, but I guess that’s the way things work in Go. When I wanted to add the functionality of Java and Go to PLC4C I was a bit stuck, as neither concept really existed. However thinking a bit more about it, adding the concept of Contexts to C was actually quite simple. Now that got me thinking: Shouldn’t we implement the same pattern for Java? It should be easy to implement. And while I was thinking, I even thought: Shouldn’t we extend this idea and also get the ReadBuffer, WriteBuffer, the Encoding, the ByteOrder and anything we’re currently passing along with “WithXYZOption” var-args, into these Contexts and simply pass along one Context object? I think this would clean up the code quite a bit. What do you think? Chris
