local raw = {}

local find = function(tbl, ind)
    for i, v in pairs(raw) do
        if v[1] == ind then
            return i,v
        end
    end
end



local mpairs = function(tbl)
    local raw = tbl.___getraw()
    return ipairs(raw)
end

local meta = setmetatable({___getraw = function() return raw end}, {
    __newindex = function(self, index, value)
        local i,v = find(raw, index)
        if v then
            if value == nil then
                table.remove(raw, i)
            else
                raw[i][2] = value
            end
        else
            table.insert(raw, {index, value})
        end
    end,
    __index = function(self, index)
        local i, v = find(raw, index)
        return v
    end,
})


meta.a = 1
meta.b = 2
meta.c = 3
meta.d = 4

for _,vals in mpairs(meta) do
    local i, v  = unpack(vals)
    print(i,v)
end