---Declare table as a base class
---@generic T
---@param cls T # class metatable
---@param o? table # initial parameters
---@return T # class instance
function Base(cls, o)
    o = o or {}
    cls.__index = cls
    setmetatable(o, cls)
    return o
end

local function search(key, bases)
    for _, base in ipairs(bases) do
        local v = base[key]     -- try `i'-th superclass
        if v then return v end
    end
end

---Declare table as a derived class
---@generic BaseT, T
---@param cls T # class metatable
---@param o? table # initial parameters
---@param ... BaseT # base class metatables
---@return T # derived class instance
function Inherit(cls, o, ...)
    o = o or {}
    local nargs = select("#", ...)
    local vargs = { select(1, ...) }
    cls.__index = cls
    if nargs > 1 then
        setmetatable(cls, {__index = function(t, k) return search(k, vargs) end})
        for _, base in ipairs(vargs) do
            o = base:new(o)
        end
    else
        local base = assert(vargs[1], "You must at least specify one class to inherit from.")
        setmetatable(cls, {__index = base})
        o = base:new(o)
    end
    setmetatable(o, cls)
    return o
end