LabVIEW Idea Exchange
I propose a property node to tell if a control was wired when This VI was called as a subVI.
Sometimes it is practical to be able to distinguish if the value in a control was wired to it (data arrived via dataflow), or if the control was unwired and the value hence the control's default value. Even comparison with the known default value of the control isn't enough, as the program logic may depend on the value source.
Consider an FG that stores two data elements:
You'll have to have two Set functions for this, one for Data 1 ("Set data 1"), and one for Data 2 ("Set data 2"). If you have only one Set function, you add the constraint that both data sets have to be present (wired) every time you set any of the two data sets, or else the unwired set will get overwritten in the FG with the default value of the unwired control. If the FG could decide programmatically if the value was wired to the control, or if it was merely the default value of the unwired control, it could decide whether to overwrite its stored copy or not. The data values could be the same in the two cases, but the actions very different. This is just a simple example, but I have many much more complex cases, that would get much simpler if I could tell where the control value came from. In the above example you could even dispose of the Function input alltogether, if I could tell if any data inputs were wired.
A polymorphic VI will remedy some of these issues, but not all, and in other cases a polymorphic VI is a drastic solution to a simple problem. It's also not an issue in a Top-level VI, as such run only once (only subVIs get called again and again, while depending on prior runs).
