Why does a Boolean Control property node input and output a Variant instead of a Boolean?

[RTSLVU]

Why does a Boolean Control Value and Value (signaling) property node input and output a Variant instead of a Boolean?

[altenbach · Accepted solution]

Latch action

[crossrulz · Accepted solution]

As Christian said, if your Boolean control is set to one of the Latch mechanical settings, the value property is a variant.

[RTSLVU]

Thanks, I see that now.

I don't use a lot of locals or property nodes and never noticed this before

[Intaris]

While I'm aware the mechanical action settings of a boolean lead to this, I feel like this is still weird behaviour.

Does anyone have a link to a discussion as to WHY it's neccessary at all to output a variant as opposed to a Boolean value? It seems like the datatype of the returned data is irrelevant in this regard.

[billko]

All right, I have to say it.  Google is your friend.  😄

I googled: "labview why latching boolean is variant" - first hit.

Spoiler

It's so you know you're doing something bad.

[RTSLVU]

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@billko wrote:

All right, I have to say it.  Google is your friend.  😄

I googled: "labview why latching boolean is variant" - first hit.

Spoiler

It's so you know you're doing something bad.

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Now that makes sense! 😛

[billko]

Older versions of LabVIEW will throw a runtime error if you insist on doing it, and it says so in the help.  But in newer versions, that tidbit is deleted from the help.  Does that mean it no longer throws an error?

[Ben]

"Why" questions are hard to answer unless we are in the room when the decision was made...

Could have to do with Latch Action terminals will change the state of the Boolean but a property node will not.

We also cannot use a local to write to a latch action Boolean.

That is all that comes to mind at the moment.

Ben

[altenbach]

Well, latch booleans reset when read by the code but it probably would be unpredictable if reading in multiple places via property nodes would each reset it. Locals aren't even allowed, while value property nodes will give you a runtime error, so the variant can never have inspectable data. So yes, seeing a variant as boolean value property means (Bad, not a boolean, don't use)

Same for writing to secondary terminal (local, value property). What should happen if you write if the button has already been pressed but not yet read? Many other scenarios. Can of worms!

Of course you might argue that writing a signaling property is more similar to actually pressing a button, so read this discussion for some perspectives.