local mytable = {}

local mt = {}

function mt.__newindex(t,k,new_value)
    local previous_value = mt[k]
    rawset(mt,k,new_value)

    if previous_value and new_value == nil then
	    print "__remove() triggered"
    end
end
mt.__index = mt

setmetatable(mytable, mt)

mytable.key = 123
print(mytable.key)

mytable.key = nil
print(mytable.key)
-- your code goes here