opus/sys/apis/class.lua

-- From http://lua-users.org/wiki/SimpleLuaClasses
-- (with some modifications)

-- class.lua
-- Compatible with Lua 5.1 (not 5.0).
return function(base)
  local c = { }    -- a new class instance
  if type(base) == 'table' then
    -- our new class is a shallow copy of the base class!
    for i,v in pairs(base) do
      c[i] = v
    end
    c._base = base
  end
  -- the class will be the metatable for all its objects,
  -- and they will look up their methods in it.
  c.__index = c

  -- expose a constructor which can be called by <classname>(<args>)
  setmetatable(c, {
    __call = function(class_tbl, ...)
      local obj = { }
      setmetatable(obj,c)
      if class_tbl.init then
        class_tbl.init(obj, ...)
      else
        -- make sure that any stuff from the base class is initialized!
        if base and base.init then
          base.init(obj, ...)
        end
      end
      return obj
    end
  })

  c.is_a =
    function(self, klass)
      local m = getmetatable(self)
      while m do
        if m == klass then return true end
        m = m._base
      end
      return false
    end
  return c
end