RE: Parameter completition

["Eric Ries" <eries@...>]

I don't understand this example. What output do you desire? Would having
functions with "optional default" arguments (as in C++) solve your problem?
Something like:

NotGiven = -1
function foo( a, b = NotGiven )
  if b == NotGiven then
     -- b was not passed in
  else if b == nil then
     -- b was passed in as "nil"
  else
     -- b was passed in with a non-nil value
  end
end

Eric

> -----Original Message-----
> From: owner-lua-l@tecgraf.puc-rio.br
> [mailto:owner-lua-l@tecgraf.puc-rio.br]On Behalf Of Markus Huber
> Sent: Thursday, January 10, 2002 4:13 PM
> To: Multiple recipients of list
> Subject: Parameter completition
>
>
> The following example shows, why I need boolean:
>
>    false = 0
>     true = 1
>
>    function Complete(Parameter,Value)
>
>       if Parameter==nil then
>          Parameter=Value
>       end
>
>       return Parameter
>
>    end
>
>
>    function Test(Parameter1,Parameter2)
>
>       Parameter2=Complete(Parameter2,true)
>
>       print(Parameter1)
>       print(Parameter2)
>
>    end
>
>    Test(3)        -- prints 3 1
>    Test(3,nil)    -- prints 3 1
>
>    Test(3,false)  -- prints 3 0
>    Test(3,true)   -- prints 3 1
>
>
> In this example if Parameter2 not given then it should be used the
> default. Is it possible to give the parameter as a reference instead of
> a copy? Then I could write much shorter: Complete(Parameter2,true)
> instead of typing the variable name twice.
>
> Its impossible to use "nil" or "not nil" for Parameter2 as a flag.
> Because "nil" is interpreted as a non given parameter.
>
> Thanks for any comments.
>
> --
> Markus
>