return multiple values from function

[manjh]

According to

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https://stackoverflow.com/questions/63044739/functions-that-return-multiple-values-lua

I can return multiple values from a single function call.
But when I try, I get an error.
this is the skeleton for the function:

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function ExtractElectrics(dev_switch, dev_volt, dev_watt, dev_kwh)
    local switch, volt, watt, kwh = ".."
    return switch, volt, watt, kwh
end

this is the call, and print for the results:

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    a, b, c, d = ExtractElectrics(dev_name1, dev_name4, dev_name2, dev_name3)
    print ("@@@@@ switch :"..a)
    print ("@@@@@ volt   :"..b)
    print ("@@@@@ watt   :"..c)
    print ("@@@@@ kwh    :"..d)

The domoticz log throws an error on the second print line. FIrst print line comes out OK.
Does this suggest I can only return one value from a function?

[boum]

your skeleton function only initialize the first local variables, all other are nil.

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function ExtractElectrics(dev_switch, dev_volt, dev_watt, dev_kwh)
    local switch, volt, watt, kwh = "a", "b", "c", "d"
    return switch, volt, watt, kwh
end

[manjh]

OK, so this version of LUA does not follow the general rule that multiple return values are supported.
I guess I'll circumvent by putting the values into an array and return that.

[jvdz]

Multiple values are supported, but in the posted example the 2nd-4h variable will be "nil" since the right-hand side function of the "=" only has one value.
I think it always has worked like this in lua.

[manjh]

Multiple values are supported, but in the posted example the 2nd-4h variable will be "nil" since the right-hand side function of the "=" only has one value.
I think it always has worked like this in lua.

So how would the statement look according to you?

[jvdz]

This should work fine assuming the parameters are all given a value

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function ExtractElectrics(dev_switch, dev_volt, dev_watt, dev_kwh)
    return dev_switch, dev_volt, dev_watt, dev_kwh
end

if there is a change that one is nil you could set the default like this:

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function ExtractElectrics(dev_switch, dev_volt, dev_watt, dev_kwh)
    return (dev_switch or '') , (dev_volt or 0), (dev_watt or 0), (dev_kwh or 0)
end

.. but i guess i am missing the point of this extra function at this moment.

[habahabahaba]

your skeleton function only initialize the first local variables, all other are nil.

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function ExtractElectrics(dev_switch, dev_volt, dev_watt, dev_kwh)
    local switch, volt, watt, kwh = "a", "b", "c", "d"
    return switch, volt, watt, kwh
end

I agree with this. It works

[manjh]

This should work fine assuming the parameters are all given a value

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function ExtractElectrics(dev_switch, dev_volt, dev_watt, dev_kwh)
    return dev_switch, dev_volt, dev_watt, dev_kwh
end

if there is a change that one is nil you could set the default like this:

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function ExtractElectrics(dev_switch, dev_volt, dev_watt, dev_kwh)
    return (dev_switch or '') , (dev_volt or 0), (dev_watt or 0), (dev_kwh or 0)
end

.. but i guess i am missing the point of this extra function at this moment.

As said, it is a skeleton. Purpose of this function will be to extract four values from a Zigbee smart switch with energy measuring function, format the values in a standard way, and return.