raii.lua

local function if_then(toclose)
    if not toclose then
        return function() end
    end
    return function (_, w)
        if not w then
            return toclose
        end
    end, nil, nil, toclose
end

local function Class(def)
    return function(...)
        local res = def.create(...)
        if not res then
            return
        end
        return setmetatable(res, { __close = def.remove })
    end
end

local human = Class {
    create = function(name)
        if #name > 4 then
            return
        end
        local w = {
            Name = name
        }
        print(w.Name, ": born")
        return w
    end,
    remove = function(w)
        print(w.Name, ": die")
    end,
}


for o in if_then(human "Alice") do
    print(o.Name, ": do")
end

for o in if_then(human "Bob") do
    print(o.Name, ": do")
end