Re: Functions with individual metatables

[Richard Hundt <richardhundt@...>]

steve donovan wrote:
[...]
> > fmeta = {}
> > fmeta.__index = fmeta
> > fmeta.attrb = 'hello'
> > debug.setmetatable(math.sin,fmeta)
> > return  math.sin.attrb
> hello
> > return  math.cos.attrb
> hello
>
> They all have the same attribute, which is probably not useful. Hence
> the need for individual metatables.

No indeed, it doesn't do boxing. I stopped thinking at the "tag a 
function" part :)

To make your test work, we need to delegate:

local func_meta = { }
setmetatable(func_meta, { __mode = "k" })

debug.setmetatable(function() end, {
   __index = function(func, key)
      local meta = func_meta[func]
      if meta and meta.__index then
         if type(meta.__index) == "function" then
            return meta:__index(key)
         else
            return meta.__index[key]
         end
      end
   end;
   __newindex = function(func, key, val)
      local meta = func_meta[func]
      if meta and meta.__newindex then
         if type(meta.__newindex) == "function" then
            return meta:__newindex(key, val)
         else
            return meta.__newindex[key]
         end
      end
   end;
   -- the rest of the meta table events here...
})

function setfmeta(func, meta)
   func_meta[func] = meta
   return func
end

function getfmeta(func)
   return func_meta[func]
end

fmeta = {}
fmeta.__index = fmeta
fmeta.attrb = 'hello'

setfmeta(math.sin, fmeta)
print(math.sin.attrb)

This all is starting to look significantly more expensive, so I'll have 
to have a little think about how to optimise it.

Cheers,
Rich