Lua properties, Lua

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--N1ghtSiren
--
local function MakeProxy(object, getters, setters)
    local proxy = {}
    
    proxy.__index = function(self, key)
        
        --debug message to indicate its work
        print("\tgetter: " .. tostring(self) .. "["..tostring(key).."]")
        
        --try to get getter on same key
        local func = getters and getters[key]
        
        if func then
            print("custom getter found on key " .. tostring(key))
            
            --calling getter (so we can just self.x = 0 later)
            return func(getmetatable(self))
        else
            
            --try to return new proxy value |or| old object value
            return rawget(getmetatable(self), key) or object[key]
        end
    end
    
    proxy.__newindex = function(self, key, value)
        
        --debug message to indicate its work
        print("\tsetter: " .. tostring(self) .. "[" .. tostring(key) .. "] = " .. tostring(value))
        
        --try to get setter on same key
        local func = setters and setters[key]
        
        if func then
            print("custom setter found on key " .. tostring(key))
            
            --call setter (so we can just self.x = 0 later)
            func(getmetatable(self), value)
        else
            
            --if setter not exists, just set directly to object
            rawset(getmetatable(self), key, value)
        end
    end
    
    return setmetatable({}, proxy)
end

--some constants
local KEY_X = "x"
local KEY_ID = "unitid"

--some constructor
function NewUnit(unitid)
    local obj = {}
    obj[KEY_ID] = unitid
    
    local proxy = MakeProxy(
        --object
        obj, 
        --getters
        {
            [KEY_X] = function(self)
                --print("getter")
                return self[KEY_X]
            end,
        },
        --setters
        {
            [KEY_X] = function(self, value)
                
                --basically you can limit types there, so it can be only number
                if(type(value) == "number")then
                    self[KEY_X] = value
                else
                    print("error: x must be 'number' type ")
                end
            end 
        }
    )
    return proxy
end

local u = NewUnit("Hpal")
u.x = 22
u.y = -10
print(u.x) -- 22

--value without defined setter - works as usual
print(u.y) -- -10

--old values before setting up proxy
print(u[KEY_ID]) -- Hpal

--changing old values
u[KEY_ID] = "HvsH"
print(u[KEY_ID]) -- HvsH

--some weird interactions
u.x = function() end -- kinda ok, but value not updates
print(u.x)
print("")

u.x = nil --same
print(u.x)
print("")

--null values
print(u.posx) --nil

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