I think ... it won't print ...

You think? What happens when you do it? 

c:\@Work\Perl\monks>perl -wMstrict -le
"my @ra;
 ;;
 sub Sa { @ra = (1,2,3); }
 ;;
 sub Sb { foreach my $n (@ra) { print $n; } }
 ;;
 Sa;
 Sb;
"
1
2
3

[download]
Note that the behavior of this code depends on execution order. The execution order  Sb; Sa; will have very different results, at least the first time. Try it!

Update: How could you make this code immune to execution order problems? One way might be: 

c:\@Work\Perl\monks>perl -wMstrict -le
"{ my @ra;
   ;;
   sub S_init { @ra = (1, 2, 3); }
   ;;
   sub S_doit {
     S_init() if @ra == 0;
     foreach my $n (@ra) { print $n; }
     }
 }
 ;;
 S_doit();
"
1
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3

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The  @ra array is defined within a lexical scope and is completely inaccessible to any code outside the scope (except by deep magick — but you didn't hear that from me). An initialization state exists for  @ra that is checked on every invocation of the  S_doit() subroutine; if the array isn't initialized, initialize it before doing anything else.

Unfortunately, this imposes the burden, which may not be small, of checking the state of  @ra (and who knows what else) on every  S_doit() invocation. Is there a way to avoid this overhead? This 

c:\@Work\Perl\monks>perl -wMstrict -le
"BEGIN {
   my @ra = (1, 2, 3);
   ;;
   sub S_doit { foreach my $n (@ra) { print $n; } }
   }
 ;;
 S_doit();
"
1
2
3

[download]
does lexical initialization at compile time and avoids the need for further thought about what happens at run time. (Update: See BEGIN, UNITCHECK, CHECK, INIT and END in perlmod for info on BEGIN (and the related INIT) blocks.)

Of course, with techniques like these, you're edging closer and closer to a full-on Object Oriented Programming approach, so why not just take the plunge?

Give a man a fish:  <%-{-{-{-<

In reply to Re^3: Accessing values outside subroutine by AnomalousMonk
in thread Accessing values outside subroutine by Anonymous Monk

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