hook

hookable.lua

function Hookable(f)
    local ret = {}
    ret.hook = {}
    setmetatable(ret, {
        __add = function(a, b)
            table.insert(ret.hook, b)
            return ret
        end,
        __call = function(...)
            f()
            for i, v in ipairs(ret.hook) do
                v()
            end
        end
    })
    return ret
end

f = function()
    print("f")
end

g = function()
    print("g")
end

ff = Hookable(f)
ff()

ff = ff + g
ff()