in reply to Lexicals in if() scope gotcha!

  1. This is not just an issue with "if" it also happens with "for" (but not foreach, or while)... 
    #!/usr/bin/perl

print "foreach...\n";
foreach (Foo->new) {}
print "after foreach\n";
print "while...\n";
while (my $object = Foo->new && 0) {}
print "after while\n";
print "for...\n";
for (my $object = Foo->new; 1 < 0; ) {}
print "after for\n";

package Foo;
sub new { my $self = bless {},shift; print "CREATED $self\n"; $self }
sub DESTROY { print "DESTROYED $_[0]\n" }

__END__

bester:~/tmp> monk.pl
foreach...
CREATED Foo=HASH(0x22494)
DESTROYED Foo=HASH(0x22494)
after foreach
while...
CREATED Foo=HASH(0x305f0)
DESTROYED Foo=HASH(0x305f0)
after while
for...
CREATED Foo=HASH(0x22494)
after for
DESTROYED Foo=HASH(0x22494)

    [download]
  2. This is why you should allways head the immortal words of perltoot...
    Perl's notion of the right time to call a destructor is not well-defined currently, which is why your destructors should not rely on when they are called.

Replies are listed 'Best First'.
Re: Re: Lexicals in if() scope gotcha!
by Mr. Muskrat (Canon) on Mar 31, 2004 at 02:51 UTC

    I got slightly different results but I also changed the foreach a bit...

    #!/usr/bin/perl

print "foreach...\n";
foreach (my $object = Foo->new) {}
print "after foreach\n";
print "while...\n";
while (my $object = Foo->new && 0) {}
print "after while\n";
print "for...\n";
for (my $object = Foo->new; 1 < 0; ) {}
print "after for\n";

package Foo;
sub new { my $self = bless {},shift; print "CREATED $self\n"; $self }
sub DESTROY { print "DESTROYED $_[0]\n" }

__END__
foreach...
CREATED Foo=HASH(0x813361c)
after foreach
while...
CREATED Foo=HASH(0x8133700)
DESTROYED Foo=HASH(0x8133700)
after while
for...
CREATED Foo=HASH(0x813cfcc)
after for
DESTROYED Foo=HASH(0x813cfcc)
DESTROYED Foo=HASH(0x813361c)

    [download]

[reply]
[d/l]
Re: Re: Lexicals in if() scope gotcha!
by QM (Parson) on Mar 31, 2004 at 02:31 UTC
    So for and foreach are not just aliases for each other, as I've seen elsewhere.

    Update: So they are aliases, but there are still 2 entities, and the entity chosen depends on context.

    -QM
    --
    Quantum Mechanics: The dreams stuff is made of

[reply]
[d/l]
[select]
      There's a for-loop, with three expressions (sometimes called "C-style for").

      There's a foreach-loop, with single scalar (sometimes implied with $_) and a list of values to be walked (sometimes called a "csh-style foreach").

      They're definitely two different kinds of loops. However the text for and foreach may be used to introduce either one. The actual loop-style is determined by what follows.

      -- Randal L. Schwartz, Perl hacker
      Be sure to read my standard disclaimer if this is a reply.

[reply]

      They are aliases. If you look, you see that for and foreach have been used differently. This should clarify that.

      #!/usr/local/bin/perl5.9.1
print "foreach1...\n";
foreach (Foo->new) {}
print "after foreach\n";                                              
+                                  

print "for...\n";
for (my $object = Foo->new; 1 < 0; ) {}
print "after for\n";                                                  
+                              

print "foreach2...\n";
foreach (my $object = Foo->new; 1 < 0; ) {}
print "after foreach\n";                                              
+                                  
package Foo;
sub new { my $self = bless {},shift; print "CREATED $self\n"; $self }
sub DESTROY { print "DESTROYED $_[0]\n" }

__END__
foreach1...
CREATED Foo=HASH(0x81249dc)
DESTROYED Foo=HASH(0x81249dc)
after foreach
for...
CREATED Foo=HASH(0x8124ac0)
after for
foreach2...
CREATED Foo=HASH(0x81249dc)
after foreach
DESTROYED Foo=HASH(0x81249dc)
DESTROYED Foo=HASH(0x8124ac0)

      [download]

      Cheers,
      Ovid

      New address of my CGI Course.

[reply]
[d/l]

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