Lua multiple parameter into table depth

Question

I currently have this code, but I feel this can be optimized much better:

local config = {
    val = 1,
    background = {
        foo = 5,
        textures = {
            bar = 'okay',
            layers = {
                alpha = 1,
                color = {
                    red = 255,
                    blue = 0,
                    green = 100
                }
            }
        }
    },
    sub = {
        val = 5,
        foo = {
            val = true,
            bar = {
            }
        }
    }
}

local function set_config(...)
    local arg = {...}
    if type(arg[1]) == 'table' then
        table.extend(config, arg[1])
    elseif #arg == 2 then
        if type(arg[2]) == 'table' then
            table.extend(config[arg[1]], arg[2])
        else
            config[arg[1]] = arg[2]
        end
    elseif #arg == 3 then
        if type(arg[3]) == 'table' then
            table.extend(config[arg[1]][arg[2]], arg[3])
        else
            config[arg[1]][arg[2]] = arg[3]
        end
    -- And now for the 4th time. This is starting to get way to repetitive
    elseif #arg == 4 then
        if type(arg[4]) == 'table' then
            table.extend(config[arg[1]][arg[2]][arg[3]], arg[4])
        else
            config[arg[1]][arg[2]][arg[3]] = arg[4]
        end
    -- And for what I try to achieve, I should continue this elseif's until indefinite
    end
end
-- And this should go as deep into the table as I want to

Now I can do

set_config('val', 3)
set_config('sub', {
    foo = false
})

But I want to go as deep into the table without the limit I have now with the set_config

So I could do

set_config('background', 'textures', 'layers', 'medium', 'color', 'red', 255)

And for clarification, the table.extend

function table.extend(t1, t2)
    for k, v in pairs(t2) do
        if (type(v) == "table") and (type(t1[k] or false) == "table") then
            table.extend(t1[k], t2[k])
        else
            t1[k] = v
        end
    end
    return t1
end

I've tried out a few things, but my Lua knowledge is rather limited.

The answer by lhf was almost correct, here is the outcome that works as i wanted it:

local function set_config(...)
    local a={...}
    local n=#a
    local t=config
    if #a == 1 and type(a[1]) == 'table' then
        table.extend(config, a[1])
        return
    end
    for i=1,n-2 do
        local k=a[i]
        t[k]=t[k] or {}
        t=t[k]
    end
    if type(t[a[n-2]]) == 'table' then
        table.extend(t[a[n-1]], a[n])
    else
        t[a[n-1]] = a[n]
    end
end

It looks like config is acting like the 'root' of the table. What can config have as keys and values? Your example above is suggesting 2 but can it also have arbitrarily many keys? — greatwolf
– greatwolf, Commented Oct 29, 2013 at 2:48
config could be a table with an unlimited depth. So it might happen that config has a key like: config.backgrounds.overlay.color.r. Or even deeper. It's variable. What i want to achieve is that i can use the set_config function to set values in the config table as deep as i give the parameters. so set_config('background', 'overlay', 'color', 'r', 255) should be possible aswell — Robin Radic
– Robin Radic, Commented Oct 29, 2013 at 3:10
I have updated my original post which hopefully clarifies what i want — Robin Radic
– Robin Radic, Commented Oct 29, 2013 at 3:27
Leave the question as it was originally and move your edit to an answer. — lhf
– lhf, Commented Oct 29, 2013 at 9:34

lhf · Accepted Answer · 2013-10-29 03:43:53Z

3

Try this:

local config={}

function set_config(...)
    local a={...}
    local n=#a
    local t=config
    for i=1,n-2 do
        local k=a[i]
        t[k]=t[k] or {}
        t=t[k]
    end
    t[a[n-1]]=a[n]
end

set_config('background', 'textures', 'layers', 'medium', 'color', 'red', 255)

print(config.background.textures.layers.medium.color.red)

answered Oct 29, 2013 at 3:43

lhf

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1 Comment

Robin Radic Over a year ago

Nevermind the comment i posted here. This works but needed a slight alteration for my needs. Thanks a bunch

dualed · Accepted Answer · 2013-10-30 18:30:31Z

1

With some metatable magic, you can get rid of set_config altogether:

local config, config_mt
config_mt = {
    __index = function(t, k)
        t[k] = setmetatable({}, config_mt)
        return t[k]
    end,
}
config = setmetatable({}, config_mt)

config.background.textures.layers.medium.color.red = 255
print(config.background.textures.layers.medium.color.red)

Though there is one downside: After restoring your config from storage you would have to iterate through the structure once in order to apply the metatables again.

answered Oct 30, 2013 at 18:30

dualed

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