Re: patching userdata metatable.... ouch!

[Edgar Toernig <froese@...>]

Just some style comments...

> SetInheritance = function(obj, parent)
>   local nmt = {}
>   local omt = getmetatable(obj)
> 
>   nmt.__index = function(object, key)
>     local omt = omt       -- Correct use of upvalues
>     local parent = parent -- to store the original
>                           -- metatable and parent?

These two locals are not necessary.  Simply use omt and
parent directly.  You only need to make local copies if
the function wants to change omt/parent and these changes
shouldn't be visible to the outer function (SetInheritance).

>     local result
> 
>     if (omt) then

The parentheses are not necessary.

>       -- There should be a simpler way to
>       -- express this lookup.
>       if (istable(omt.__index) then

Same as above.

>         result = omt.__index[key]
>       else
>         result = omt.__index(object, key)
>       end
>     end
> 
>     if result then return result end
> 
>     return parent[key]

The last 3 lines are often written as

    return result or parent[key]

>   end
> 
>   -- Presumably we need a C function to call
>   -- setmetatable for us because Lua code
>   -- isn't allowed to set metatables for
>   -- a userdata
>   application:SetObjectMetatable(obj, nmt)
> end

Ciao, ET.