in reply to if(my) scope

if is implemented in terms of and, and neither creates a scope at run-time (i.e. they don't call ENTER+LEAVE). That means they don't affect the life (refcount) of variables.

if only affects the visibility of the variable, a compile-time effect.

yuck!

Update: Just to be clear, I'm talking specifically about the condition expression, not the body of the if.

Replies are listed 'Best First'.
Re^2: if(my) scope
by cdarke (Prior) on Apr 16, 2009 at 15:44 UTC
    Although I am sure you are right, how come:
    use strict;
use warnings;
use Devel::Peek;

my $true = 1;
my $ref;

if ($true)
{
    my $fred = 42;
    $ref = \$fred;
}

print Dump($$ref);

    [download]
    Gives:
    SV = IV(0x3b2e0) at 0x3b2e4
  REFCNT = 1
  FLAGS = (PADMY,IOK,pIOK)
  IV = 42

    [download]
    A reference count of 1, not 2?
[reply]
[d/l]
[select]
      You changed
      if (my $var) { ... }
      to
      if (...) { my $var; ... } 
      use strict;
use warnings;
use Devel::Peek;

my $ref;

if ((my $fred = 42), 1)
{
    $ref = \$fred;
    Dump($$ref);
}

Dump($$ref);

      [download]
      SV = IV(0x816a5cc) at 0x814f684
  REFCNT = 2
  FLAGS = (PADBUSY,PADMY,IOK,pIOK)
  IV = 42
SV = IV(0x816a5cc) at 0x814f684
  REFCNT = 2
  FLAGS = (PADBUSY,PADMY,IOK,pIOK)
  IV = 42

      [download]

      A scope is created for if's curlies, but only a compile-time scope is created for the condition expression.

      Btw, note the proper usage of Dump.

[reply]
[d/l]
[select]
        Doh!
[reply]
Re^2: if(my) scope
by oha (Friar) on Oct 12, 2009 at 08:53 UTC
    i just realized that: 
    open my $fh, '<', $file or die;

    [download]
    so i'm asking myself if the possibility to setup a scope variable inside the argument of a function call is extended to _if_ statements too?
[reply]
[d/l]

      This is fine: 

      if (open(my $fh, '<', $qfn)) {
    ...read from $fh...
}

# $fh is out of reach here

      [download]

      Perl doesn't care where the my is to the point that it allows the following (even though the behaviour is officially undefined): 

      my $fh if ...;

      [download]
[reply]
[d/l]
[select]
        that's another thing: 
        if(my $x = expr) { ... } # my always executed
my $x if expr;           # my is conditional
if(expr) { my $x }       # as above

        [download]
        what i was saying is that if i can my on a arg of a function, maybe i can do the same in the "argument" of a if

        Oha

[reply]
[d/l]

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