Is it possible to make a collapsing variables without making individual functions?

Question

I have a code that starts as a small amount of variables and makes more elements using those initial variables.

function new( x, y, width, height )
    local obj         


        

Answer 1

I was bored and saw this question (again) along with a duplicate. I started writing some code for fun, leading to this:

local function getNeededVars(tab,func)
    local needed,this = {}
    this = setmetatable({},{
        __index = function(s,k)
            -- See if the requested variable exists.
            -- If it doesn't, we obviously complain.
            -- If it does, we log it and return the value.
            local var = tab.vars[k]
            if not var then
                error("Eh, "..k.." isn't registered (yet?)",5)
            end needed[k] = true return tab.vals[k]
        end;
    }) func(this) return needed
end

local function updateStuff(self,key,done)
    for k,v in pairs(self.levars) do
        if v.needed and v.needed[key] then
            if not done[v] then done[v] = true
                self.vals[v.name] = v.func(self)
                updateStuff(self,v.name,done)
            end
        end
    end
end

local function createSubTable(self,key,tab)
    return setmetatable({},{
        __newindex = function(s,k,v)
            tab[k] = v updateStuff(self,key,{})
        end; __index = tab;
    })
end

local dependenceMeta
dependenceMeta = {
    __index = function(self,k)
        -- Allow methods, because OOP
        local method = dependenceMeta[k]
        if method then return method end
        local variable = self.vars[k]
        if not variable then
            error("Variable "..k.." not found",2)
        end return self.vals[k]
    end;
    __newindex = function(self,k,v)
        local variable = self.vars[k]
        if not variable then
            error("Use :Register() to add stuff",2)
        elseif type(v) == "table" then
            self.vals[k] = createSubTable(self,k,v)
            return updateStuff(self,k,{})
        end self.vals[k] = v updateStuff(self,k,{})
    end
}
function dependenceMeta:Register(var,value)
    local varobject = {func=value,name=var}
    self.vars[var] = varobject
    table.insert(self.levars,varobject)
    if type(value) == "function" then
        varobject.needed = getNeededVars(self,value)
        self.vals[var] = value(self)
    elseif type(value) == "table" then
        self.vals[var] = createSubTable(self,var,value)
    elseif value then
        self.vals[var] = value
    end
end
function dependenceMeta:RegisterAll(tab)
    for k,v in pairs(tab) do
        self:Register(k,v)
    end
end

local function DependenceTable()
    return setmetatable({
        levars = {};
        vars = {};
        vals = {};
    },dependenceMeta)
end

local test = DependenceTable()
test:Register("border",{
    x=20; y=50;
    height=200;
    width=100;
})
test:Register("body",function(self)
    return {x=self.border.x+1,y=self.border.y+1,
        height=self.border.height-2,
        width=self.border.width-2}
end)
test:Register("font",function(self)
    local size = (self.body.height+2)-(math.floor((self.body.height+2)/4)+1);
    return { size = size; -- Since we use it in the table constructor...
        height = size-4; --love.graphics.setNewFont( self.font.size ):getHeight();
        -- I don't run this on love, so can't use the above line. Should work though.
    }
end)
test:Register("padding",function(self)
    local height = math.floor(self.border.height*(2/29))
    return { height = height; width = height*3 } -- again dependency
end)
test:Register("text",{input=""}) -- Need this initially to keep input
test:Register("text",function(self)
    return { input = self.text.input;
        centerHeight = math.ceil(self.body.y+((self.body.height-self.font.height)/2));
        left = self.body.x+self.padding.width+self.padding.height;
    }
end)
test:Register("backspace",{key = false, rate = 3, time = 0, pausetime = 20, pause = true})
-- Again, didn't use gui.id() on the line below because my lack of LÖVE
test:Register("config",{active=true,devmode=false,debug=false,id=123,type='textbox'})

print("border.x=20, test.text.left="..test.text.left)
test.border = {x=30; y=50; height=200; width=100;}
print("border.x=30, test.text.left="..test.text.left)
test.border.x = 40
print("border.x=40, test.text.left="..test.text.left)

It's a lot of code, but I liked writing it. It gives this nice output:

border.x=20, test.text.left=73
border.x=30, test.text.left=83
border.x=40, test.text.left=93

All properties only get recalculated when one of its dependencies is edited. I made it also work with subtables, which was a bit tricky, but at the end actually seems quite easy. You can edit (for example) the body field by setting it to a completely new table or by setting a field in the already existing table, as seen in the last few lines of the code snippet. When you assign it to a new table, it'll set a metatable on it. You can't use pairs (& co) neither, unless you use 5.2 and can use __pairs.

It might solve your problem. If not, I had fun writing it, so at least it'll always be something positive that I wrote this. (And you have to admit, that's some beautiful code. Well, the way it works, not the actual formatting)

Note: If you're gonna use it, uncomment the love.graphics and gui.id part, as I don't have LÖVE and I obviously had to test the code.

Here's a quick "summary" of my thing's API, as it might be confusing in the beginning:

local hmm = DependenceTable() -- Create a new one
print(hmm.field) -- Would error, "field" doesn't exist yet

-- Sets the property 'idk' to 123.
-- Everything except functions and tables are "primitive".
-- They're like constants, they never change unless you do it.
hmm:Register("idk",123)
-- If you want to actually set a regular table/function, you
-- can register a random value, then do hmm.idk = func/table
-- (the "constructor registering" only happens during :Register())

-- Sets the field to a constructor, which first gets validated.
-- During registering, the constructor is already called once.
-- Afterwards, it'll get called when it has to update.
-- (Whenever 'idk' changes, since 'field' depends on 'idk' here)
hmm:Register("field",function(self) return self.idk+1 end)
-- This errors because 'nonexistant' isn't reigstered yet
hmm:Register("error",function(self) return self.nonexistant end)
-- Basicly calls hmm:Register() twice with key/value as parameters
hmm:RegisterAll{
    lower = function(self) return self.field - 5 end;
    higher = function(self) return self.field + 5 end;
}
-- This sets the property 'idk' to 5.
-- Since 'field' depends on this property, it'll also update.
-- Since 'lower' and 'higher' depend on 'field', they too.
-- (It happens in order, so there should be no conflicts)
hmm.idk = 5
-- This prints 6 since 'idk' is 5 and 'field' is idk+1
print(hmm.field)

You could use setfenv (if Lua 5.1) to remove the need of 'self.FIELD'. With some environment magic you can have the constructor for 'field' (as an example) just be function() return idk+1 end.