Is there a select statement?

[manjh]

Hopefully there is a simple answer to this...

In other programming languages I can use the select statement to execute parts of code depending on content of a variable.

For instance:

Assume variable x has a numeric value.

Select (x)
when (1) do
...
end
when (2) do
...
end
otherwise
...
end
end

I know I could do this using if-then-elseif etcetera, but the select would be much cleaner....

Is there something like this?

[Kedi]

In https://www.lua.org/manual/5.1/manual.html you can see that the select statement is used for somewhat different.
What would be the benefit over "if then elseif end" method?

[lost]

The C-like switch/case is not present in Lua (was same for very long with Python as well), usual advice to avoid heavy if/elseif usage is to rework the logic using what is the basis of this language: Tables...
http://lua-users.org/wiki/SwitchStatement

That's one among C oldies I often miss using Lua or Python, others being static variables and ternary operator: There is always some tricks, but not being a language feature I always have to remember/search when needed.

[manjh]

Maybe I should explain the purpose I wanted this for.
I use a UserVariable to store a value, coming out of a number of NFC sources.
Each value represents a specific command: like "turn on lights", "turn off ventilation", "toggle driveway spotlight", etcetera.
My routine picks up that uservariable, and then executes a specific subroutine.

One way to do it would be to name the subroutine with the value and then call it using the variable.
For example: name the subroutine "1", and then find a way to call that directly using the uservariable.
Unfortunately I see no way to do this in LUA.

The article pointed at by "lost" in this thread, shows many interesting workarounds to do it.
But I guess for now I'll stick to the if-then-elseif list.

[jvdz]

Can't you simply store them in an array using the number as key? That way you should be able to get the command with array[key].

[manjh]

Can't you simply store them in an array using the number as key? That way you should be able to get the command with array[key].

Not sure what you mean. Store what in an array? Get what command?
Could you give a small example?

[FlyingDomotic]

Idea, for a switch number between 3 and 6, to use something like:

Code: Select all

array[3] = "AAAA"
array[4] = "BBBB"
array[5] = "CCCC"
array[6] = "DDDD"
if number >= 3 and number <=6 then
   print(array[number])
else
   print("Number out of 3-6 range")
end

[HvdW]

If - elseif:

Code: Select all

local x = 2  -- Example value

if x == 1 then
    -- Code to execute when x is 1
    print("x is 1")
elseif x == 2 then
    -- Code to execute when x is 2
    print("x is 2")
else
    -- Code to execute for all other cases
    print("x is something else")
end

or:

Code: Select all

local x = 2  -- Example value

local actions = {
    [1] = function()
        -- Code to execute when x is 1
        print("x is 1")
    end,
    [2] = function()
        -- Code to execute when x is 2
        print("x is 2")
    end
}

local action = actions[x] or function()
    -- Code to execute for all other cases
    print("x is something else")
end

action()  -- Execute the corresponding function

like:

Code: Select all

return {
    on = {
        devices = { 'MyDevice' }
    },
    execute = function(domoticz, device)
        local x = device.state  -- Assuming the device state is a numeric value

        local actions = {
            [1] = function()
                domoticz.log("x is 1", domoticz.LOG_INFO)
                -- Additional actions for x == 1
            end,
            [2] = function()
                domoticz.log("x is 2", domoticz.LOG_INFO)
                -- Additional actions for x == 2
            end
        }

        local action = actions[x] or function()
            domoticz.log("x is something else", domoticz.LOG_INFO)
            -- Additional actions for other cases
        end

        action()  -- Execute the corresponding function
    end
}

[manjh]

If - elseif:

Code: Select all

local x = 2  -- Example value

if x == 1 then
    -- Code to execute when x is 1
    print("x is 1")
elseif x == 2 then
    -- Code to execute when x is 2
    print("x is 2")
else
    -- Code to execute for all other cases
    print("x is something else")
end

or:

Code: Select all

local x = 2  -- Example value

local actions = {
    [1] = function()
        -- Code to execute when x is 1
        print("x is 1")
    end,
    [2] = function()
        -- Code to execute when x is 2
        print("x is 2")
    end
}

local action = actions[x] or function()
    -- Code to execute for all other cases
    print("x is something else")
end

action()  -- Execute the corresponding function

like:

Code: Select all

return {
    on = {
        devices = { 'MyDevice' }
    },
    execute = function(domoticz, device)
        local x = device.state  -- Assuming the device state is a numeric value

        local actions = {
            [1] = function()
                domoticz.log("x is 1", domoticz.LOG_INFO)
                -- Additional actions for x == 1
            end,
            [2] = function()
                domoticz.log("x is 2", domoticz.LOG_INFO)
                -- Additional actions for x == 2
            end
        }

        local action = actions[x] or function()
            domoticz.log("x is something else", domoticz.LOG_INFO)
            -- Additional actions for other cases
        end

        action()  -- Execute the corresponding function
    end
}

Thank you! This is EXACTLY what I was looking for!

[manjh]

For everyone that is interested, I found an elegant way to solve my coding problem.
It starts with a UserVariable that contains an integer value. For each unique value of that UserVariable, I create a function, called NFCn.
This is the code to call the right function, based on the uservariable:

Code: Select all

-- run through all changed variables
local myVariable = "NFC"
for variableName,variableValue in pairs(uservariablechanged) do
    -- check if NFC value was changed
    if (variableName == myVariable) then
        -- found it. Now compose function name
        local FunctionName = variableName..variableValue
        -- if function exists, call it. Else report.
        if (_G[FunctionName] ~= nil) then
            _G[FunctionName]()
        else 
            print(FunctionName.." does not exist")
        end        
    end
end

This shows a very compact and elegant way to do it, much smaller than the if-then-elseif-etcetera construct!
(The functions are not shown in this code snippet, but are not difficult)

[Kedi]

Why run through all changed variables, instead of

Code: Select all

return {
    on = {
        variables = { 'NFC' }
    },
    execute = function(dz, item)
        ... do stuff
    end
}

[manjh]

Why run through all changed variables, instead of

Code: Select all

return {
    on = {
        variables = { 'NFC' }
    },
    execute = function(dz, item)
        ... do stuff
    end
}

This is dzvents, I wanted to stick to pure LUA...
But you're right. Instead of looping through the whole list of uservariables, I could just check for uservariablechanged[myVariable].