Re: Lua 5.1 varargs with nil question

[Adrian Sietsma <adrian_groups@...>]

Norman Ramsey wrote:
> I have some code that uses Lua 5.0 and has varargs functions
> in which some arguments may be nil.  Here is an example using Lua 5.0:
>
>   local output
>     --- function to output zero or more items, where an item is
>     ---    * a string
>     ---    * nil (ignored)
>     ---    * a function returning zero or more items
>     ---    * a list of items in a Lua table
>   do
>     local output_funs = { }
>     output_funs['string']   = output_one
>     output_funs['nil']      = function() end
>     output_funs['table']    = function(t) return output(unpack(t)) end
>     output_funs['function'] = function(f) return output(f()) end
>     function output(...)
>       for i = 1, table.getn(arg) do --- can't use ipairs b/c arg might be nil
>         local v = arg[i]
>         assert(output_funs[type(v)], "Bad value to output()") (v)
>       end
>     end
>   end
>
> I am struggling to figure out how to implement this function in Lua 5.1.
> How am I to make sure that I get all the arguments when the new #
> operator is not specified when some arguments are nil?  
AFAIK, #... will return the total number of items in the ... object, 
including nils.
The problems with nil args only apply to tables as arrays.


(untested)
function output(...)
   for i = 1, select('#',...) do
      local v = select(i,...)
      assert(output_funs[type(v)], "Bad value to output()") (v)
   end
end

Adrian