Re: unpack() behaviour not as documented

["Thomas Harning Jr." <harningt@...>]

On Wed, Jun 10, 2009 at 4:48 PM, Sam Roberts<vieuxtech@gmail.com> wrote:
> function get_stuff(...)
>    local r = {}
>    for i,k in ipairs{...} do
>        r[i] = stuff[k]
>    end
>    return unpack(r, 1, #...) -- #... is 3 when there are 3 args to
> this function
> end
>
> red, magenta, green = get_stuff("red", "magenta", "green")
>
> print(stuff.red, " should eql ", red)
> print(stuff.magenta, " should eql ", magenta)
> print(stuff.blue, " should eql ", blue) -- but the [3] was not returned
One useful thing to note is that if you want to pack variable
arguments into a table and not lose track of the end, you can do the
following:

local packed = {n = select('#', ...), ...}
That way you store the number of var-args (what select('#') does) and
keep all the values that were in there.
... now... if you don't need to persist the var-arg, it might be best
to take the var-arg and iterate over it, either using select, or a
lisp-like handling.

Ex:

local function for_each_vararg(fn, value, ...)
  fn(value)
  if select('#', ...) > 0 then
    return for_each_vararg(fn, ...)
  end
end

... or if you don't care about nils
local function for_each_vararg(fn, value, ...)
  if not value then return end
  fn(value)
  return for_each_vararg(fn, ...)
end




-- 
Thomas Harning Jr.