Re: string.gsub accepting a callable userdata

[Jerome Vuarand <jerome.vuarand@...>]

2012/12/13 David Favro <lua@meta-dynamic.com>:
>> local gsub,type = string.gsub,type
>> local ref = setmetatable({}, {__weak='v'})
>> local function unref(...) return ref[1](...) end
>>
>> function string.gsub(s,pat,repl)
>>     if type(repl) == 'userdata' then
>>        ref[1] = repl
>>        repl = unref
>>     end
>>     return gsub(s,pat,repl)
>> end
>
>
> Wouldn't this be non-reentrant should the called userdata itself call gsub()
> [or cause it to be called via loaded script]?  ref[1] would now be the inner
> gsub()'s repl, and when the outer gsub() finds another match it will call
> unref() again which will dereference to the wrong repl.

Yes, you are totally right, since there is only one ref and one unref,
if two gsub calls end up on the call stack, one will certainly have a
wrong reference. I guess the only (simple) solution to the problem
then is to create a closure for each gsub call.