lua-users home
lua-l archive

[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index] [Thread Index]

> CarMetatable =
> {
> __newindex = function(table, key)
>    return rawget(Vehicle, key) or  -- "inherit from Vehicle"
>    return rawget(Engine, key) or   -- "inhereit from Engine"
>    return rawget(Wheels, key) end  -- "inherent from Wheels"
> }

Yup, it is easy enough. A couple of quibbles:

1) The use of rawget means that you will not be able to chain
inheritance. (i.e. if Vehicle inherits from something, then Car
won't acquire that.) I would just use an index:

  Vehicle[key] or Engine[key] or Wheels[key]

2) "return" doesn't actually have a value. I think you probably
didn't mean to type it three times.

3) You have to watch out for the false/nil dichotomy; the code
as presented will treat false as though it were nil, preventing
you from inheriting the value of a boolean member (if the 
member's value is false). If that is possible, you need to
write somewhat more elaborate tests, something like this:

  local rv = Vehicle[key]
  if rv == nil then rv == Engine[key] else return rv end
  if rv == nil then rv == Wheels[key] end
  return rv