How he handles the labview to more generic class

It's just a matter for my own knowledge of curious nerd. If you, say, have a cluster that contains a string, a Boolean value, and a digital control, a common method to reference the controls in the cluster is to create a cluster of reference and then to get the array of control from a property node. So let's say I wanted to put the Boolean value true, you can auto control array index and cast in more specific class boolean and set value via the property node (see below).

Now my question is, to place controls of different types in a table must be returned by the property node, they must all be of the same class. How LabVIEW manages it? He cast as a more generic class backstage? If so, how this work because it is generally dangerous to come back from a class derived from a base class because the data can or will be lost.

Furthermore, a standard molded type takes just a binary model and interperates as differently it based on the data type. So how is "of a more specific class" able to raise an error if a generic control reference cannot be transformed into a class more specific. For example, in the attached photo, a control string reference would be mistake out there, but how? They are all classes of generic control when they get out of the property node. Is there some type of indicator in the generic control reference indicating the type? Maybe I think about this fundemtally wrong. All I can think is that the more specific / are more generic vi no type casting (which I guess they are not because it has separate type cast feature).

Can someone explain how this all works. Inquiring minds want to know.

for (imstuck) wrote:

Now my question is, to place controls of different types in a table must be returned by the property node, they must all be of the same class. How LabVIEW manages it? He cast as a more generic class backstage? If so, how this work because it is generally dangerous to come back from a class derived from a base class because the data can or will be lost.

Furthermore, a standard molded type takes just a binary model and interperates as differently it based on the data type. So how is "of a more specific class" able to raise an error if a generic control reference cannot be transformed into a class more specific. For example, in the attached photo, a control string reference would be mistake out there, but how? They are all classes of generic control when they get out of the property node. Is there some type of indicator in the generic control reference indicating the type? Maybe I think about this fundemtally wrong. All I can think is that the more specific / are more generic vi no type casting (which I guess they are not because it has separate type cast feature).

Can someone explain how this all works. Inquiring minds want to know.

I don't know all the details, but I would say you got it mostly right - there is an implicit conversion to a more generic type.  You will see this in several places in LabVIEW, for example, you can wire references to different types of controls in "table to build" to get a picture of their more specific common parent.  Because you're only casting reference - not the data that it contains, there is no loss of data.  A LabVIEW reference is just an I32 is (I assume) an index into a lookup table somewhere.  The value of this I32 does not change when it is converted into a more generic reference.  When you do "to more specific Type", LabVIEW raises this reference in the table and uses the data it found to determine if she can make the cast.  Who help me?

Tags: NI Software

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