POV-Ray : Newsgroups : povray.newusers : Ignorance rules! : Re: Ignorance rules! Server Time
23 Jun 2021 03:38:15 EDT (-0400)
  Re: Ignorance rules!  
From: Alain Martel
Date: 23 Jun 2020 12:13:57
Message: <5ef22a45$1@news.povray.org>
Le 2020-06-23 à 04:42, jr a écrit :
> hi,
> 
> Cousin Ricky <ric### [at] yahoocom> wrote:
>> Warning: non-newbies will face palm.  Three times.
> 
> :-)
> 
>> ...  One just has to keep in mind POV-Ray's scope leakage
>> problems[2] when choosing names:
>> ...
>>     - Once *any* identifier is declared, it cannot be reused as a macro
>>       name.
> 
> maybe I misunderstand.  the following works on alpha.10064268.unofficial
> 
> -----<snip>-----
> #version 3.8;
> 
> global_settings {assumed_gamma 1}
> 
> #declare A = 0;
> 
> #undef A
> 
> #macro A(b_)
>    b_
> #end
> 
> #declare B = A(1);
> 
> #debug concat("B = ",str(B,0,0),"\n")
> -----<snip>-----
> 
> (if you remove the '#undef', ie try to create macro with same name while the
> identifier still _is_in_use_, error "expected undeclared identifier" occurs.
> which is as it should be, aiui)
> 
> regards, jr.
> 
> 

Well, that's precisely the purpose of #undef.
After the #undef statement, you are in a state similar to that of that 
identifier never having even existed.


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