in reply to Re: goto &sub and local question
in thread goto &sub and local question

That's what I thought too, but as it was pointed out above, it is not correct, and if I had read the docs instead of trusting my memory, I wouldn't have posted this question. After all, the docs clearly say that localization is undone.

Whether this is a nice concept or not, is another question. It seems that when you want to pass control to another sub without creating a new stack frame, the only possibility to pass additional information accross the goto &... boundary is by using global (non-localized) variables.

OTOH, I think the occasions to use such a construct are so rare that it's not so bad to use a non-localized global variable for this task. </c>

-- 
Ronald Fischer <ynnor@mm.st>

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Re^3: goto &sub and local question
by almut (Canon) on Nov 24, 2008 at 09:41 UTC
    the only possibility to pass additional information accross the goto &... boundary is by using global (non-localized) variables.

    Depending on the use case you might be able to pass the data via @_: 

    sub s1 {
    my $data = pop;
    print Dumper $data;
}

sub s0 {
    push @_, [45, 'D'];
    goto &s1;
}

s0;

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    The details of how to do it without interfering with any existing arguments largely depend on the specific use case.

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      Great idea, thanks a lot! In my case, it would be unshift instead of push, and it would do exactly what I wanted.

      -- 
      Ronald Fischer <ynnor@mm.st>
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Re^3: goto &sub and local question
by Bloodnok (Vicar) on Nov 24, 2008 at 09:46 UTC
    Mmm, I wasn't questioning the localisation per-se, but the fact that your use of local (pun unavoidable:-) doesn't localise a global variable - which the docs say it does/should - rather, it purports to declare a global variable, which AFAICT, you can't from within non-global scope.

    All that being said, it does rather assume that global is seen as a true global i.e. a package global variable c/w a variable declared to be accessible from the point of declaration down...

    There now, you should be as confused as I am ;-)

    A user level that continues to overstate my experience :-))
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Re^3: goto &sub and local question
by SuicideJunkie (Vicar) on Nov 24, 2008 at 17:39 UTC
    What about this: It definitely isn't global, although it is shared between the two functions. 
    {
  my %familySecrets;
  sub s1
  {
    # Read family secrets
  }

  sub s2
  {
    #write family secret
    #call s1
  }
}

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      If you plan on initializing %familySecrets, you need to use a BEGIN block if you are in main. In a module, this isn't necessary. Technically, you can use any one of the other special named blocks that run before your code: BEGIN, UNITCHECK, CHECK, or INIT. See perlmod for more details on these blocks. 

      {
    my %familySecrets;
    BEGIN { 
        %familySecrets = ( 
            closet           => 'skeleton', 
            herbs_and_spices => 11,
            coke_recipe      => 'sugar, water, shoe polish',
        ); 
    }
  sub s1
  {
    # Read family secrets
  }

  sub s2
  {
    #write family secret
    #call s1
  }
}

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      TGI says moo

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        No need to introduce a new block. You can just add BEGIN in front of the existing curlies. 

        BEGIN {
   my %familySecrets = ( 
      ...
   ); 

   sub s1 {
      ...
   }

   sub s2 {
      ...
    }
}

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        By the way, BEGIN is probably not needed in the main script either, but there's no harm in using it.

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