Use the set_up/tear_down functions themselves as keys

[katcipis]

Something like this:

function Signal:add_set_up(set_up_func)

    if (type(set_up_func) ~= "function") then 
        error("add_set_up: expected function...") 
    end

    if not self.set_up_funcs[set_up_func] then
        self.set_up_funcs[#self.set_up_funcs+1] = set_up_func
        self.set_up_funcs[set_up_func] = #self.set_up_funcs
    end
end

function Signal:remove_set_up(set_up_func)
    local pos = self.set_up_funcs[set_up_func]
    if pos then
        table.remove(self.set_up_funcs, pos)
        self.set_up_funcs[set_up_func] = nil
    end
end

The con is that we will have a larger table. The pro is faster lookup ( O(1) instead of O(n) ) of the position of the function (used to check if a function is already inserted and to remove it).

[katcipis]

This one seens to be neat to, lets implement it

[ppizarro]

lets do it

[katcipis]

-closed by d9d294228efde744dfefb37f57127147a558432b and extends the idea to connect too