Re: Metamethods and inheritance

[Dirk Laurie <dirk.laurie@...>]

2017-10-31 13:32 GMT+02:00 Ulrich Schmidt <u.sch.zw@gmx.de>:
> I suggest, you take a look into middleclass[1]
> how they do. But "__index"-ing from one table to the next to the next to the
> next .... is time consuming, so take care.
>
> [1]: https://github.com/kikito/middleclass

OK, I have looked, and unless I totally misunderstand the code, the
parent class knows which subclasses it has, and propagates missing
methods into them.

I've designed a different mechanism, but it also involves keeping a
table of subclass metatables.

local metamethod = function(name)
  return function(record,...)
    local mmt = meta[record.tag]
    local mm = assert(mmt and mmt[name],"No metamethod "..name..
      " defined for "..record.tag)
    return mm(record,...)
  end
end

-- metamethods for ~ + - to be supplied per tag
for mm in ("bnot,add,sub"):gmatch"%l+" do
  mm = '__'..mm
  RECORD[mm] = metamethod(mm)
end

`record.tag` is the name used as key in `meta` for the OBJ's.