Simple get/set proxy for a table on Lua

deep_proxy.lua

Document = {}

function Document.new (raw)
    local doc = {}
    Document.attach_deep_proxy(raw, doc)

    return doc
end

function Document.attach_deep_proxy (raw, doc, path)
    if path == nil then
        path = {}
    end

    for key, value in pairs(raw) do
        if type(value) == 'table' then
            local sub_path = table.icopy(path)
            push(sub_path, key)

            doc[key] = {}
            Document.attach_deep_proxy(value, doc[key], sub_path)
        end
    end

    setmetatable(doc, {
        __index = function (_, key)
            Document._get(raw, key, doc, path)
            return raw[key]
        end,
        __newindex = function (_, key, value)
            raw[key] = value
            if type(value) == 'table' then
                local sub_path = table.icopy(path)
                push(sub_path, key)

                rawset(doc, key, {})
                Document.attach_deep_proxy(value, rawget(doc, key), sub_path)
            end

            Document._set(raw, key, value, doc, path)
        end,
        __len = function ()
            return #raw
        end
    })
end

function Document._get (raw, key, doc, path)
    print(':get', key, 'at', table.concat(path, '->'))
end

function Document._set (raw, key, value, doc, path)
    print(':set', key, 'at', table.concat(path, '->'), 'to', value)
end