Re^3: Lexical scoping like a fox

Excellent tutorial for me(newbie)
and yes Hugo, your example made it clear for me as I wrote out your example

use strict;

sub foo {
   print "\$a is ", defined($a) ? $a : 'undef', $/;
   print "\$b is ", defined($b) ? $b : 'undef', $/;
}


print "Just before start of scope\n";
{
  print "Just after start of scope\n";
  my $a = 1;
  local $b = 1;
  print "a=$a, b=$b\n";
  foo();
  print "Just before end of scope\n";
}
print "Just after end of scope\n";
print "\$a is ", defined($a) ? $a : 'undef', $/;
print "\$b is ", defined($b) ? $b : 'undef', $/;
[download]

Couple other questions/comments
1)using input record separator as newline indicator is very interesting. Never seen it before but works well. Any reason?
I am assuming it's just a style issue?
2)Below code from tutorial does not work when I insert my next to variable.. can someone explain this?

[root@myserver tmp]# cat -n !$
cat -n ./per_begin.pl1
     1  #!/usr/bin/perl -w
     2
     3  use strict;
     4
     5
     6  my $x = "original state";
     7
     8  sub foo {
     9      print " \$x is: $x\n";
    10  } 
    11
    12  { # beginning of lexical scope
    13
    14      local $x = "altered state";
    15      foo();
    16      
    17  } # end of lexical scope
    18  print "\$x is: $x\n";
[root@myserver tmp]# ./!$
././per_begin.pl1
Can't localize lexical variable $x at ././per_begin.pl1 line 14.
[download]

3)can someone explain further on "lexical variables are declared at compile-time, not initialised?
Is this because BEGIN runs during compile-time? I sneaked in a new my $foo = something inside of BEGIN
block and execution of the code came out w/ foo is something during BEGIN phase

Comment on Re^3: Lexical scoping like a fox Select or Download Code

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Re^4: Lexical scoping like a fox by shmem (Chancellor) on Jan 13, 2008 at 19:07 UTC
1)using input record separator as newline indicator is very interesting. Never seen it before but works well. Any reason? I am assuming it's just a style issue? I guess it's more along "a \n is a \n is a \n" - $/ is a global, and that could be changed far away without you knowing it; so it's more safety than style. 2)Below code from tutorial does not work when I insert my next to variable.. can someone explain this? You are allocating a lexical $x, not a package global (which would be either `use vars '$x'` or `our $x`), and local aliases only package globals. You can't (shouldn't) allocate globs and lexicals of the same name in the same scope: `our $x; my $x; # gives a warning` [download] `our $x; { my $x; # ok }` [download] 3)can someone explain further on "lexical variables are declared at compile-time, not initialised? Is this because BEGIN runs during compile-time? I sneaked in a new my $foo = something inside of BEGIN block and execution of the code came out w/ foo is something during BEGIN phase "lexical variables are declared at compile-time, not initialised" means "the container is created, but nothing is put into it". The initialization (= puting something into the bucket) happens at run time. BEGIN blocks are compiled and immediately run, that's why "code came out w/ foo is something during BEGIN phase". See also my/local, space/time (was: Re: The difference between my and local). --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l] [select]
Re^4: Lexical scoping like a fox by graff (Chancellor) on Jan 13, 2008 at 17:58 UTC
3)can someone explain further on "lexical variables are declared at compile-time, not initialised? It's the difference between "existing but having an undefined value (what you get when a variable is declared but not initialized -- ie. `defined($var)` returns false) vs. "existing with a defined value (what you get when you declare and initialize).	[reply] [d/l]


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