It seems to me that "my $x" has gone out of scope by the time the anon sub runs...

It has.

is the value still around because there remains a ref to it?

Yes.

If so, what is doing the ref... the anon sub itself?

No, not in my book. The reference to the anonymous sub is a special type of "code ref" called a closure (yes, we all knew that by now). This closure (the code ref) is what holds a reference to the lexical (and not the anonymous sub which is separate from the reference in my book -- especially since the anonymous sub is not recompiled every time you take another reference to it).

So $h holds (something that contains) a reference to the $x that was set to "Howdy" while $g holds a reference to the $x that was set to "Greetings".

Make $x an object and you can see that destroying $h triggers a destructor, etc: 

#!/usr/bin/perl -w
use strict;

sub Obit::new {
    my( $this, $ref )= @_;
    my $desc= "$ref";
    $desc .= " (${$ref})"   if  UNIVERSAL::isa( $ref, "SCALAR" );
    warn "$desc is born.\n";
    return bless $ref, $this;
}
sub Obit::DESTROY {
    my $self= shift;
    my $desc= "$self";
    $desc .= " (${$self})"   if  $self->isa("SCALAR");
    warn "$desc has died.\n";
}

sub newprint {
  my $x= Obit->new( \shift );
  return sub { my $y= shift; print "${$x}, $y!\n"; };
}

$|= 1;
{
    my $h= Obit->new( newprint("Howdy") );
    warn "About to destroy \$h.\n";
}
warn "\$h is no more.\n";
{
    my $g= Obit->new( newprint("Greetings") );
    warn "About to destroy \$g.\n";
}
warn "\$g is no more.\n";
__END__
SCALAR(0x1bbefc0) (Howdy) is born.
CODE(0x1bbf074) is born.
About to destroy $h.
Obit=CODE(0x1bbf074) has died.
Obit=SCALAR(0x1bbefc0) (Howdy) has died.
$h is no more.
SCALAR(0x1bb50d4) (Greetings) is born.
CODE(0x1bbf074) is born.
About to destroy $g.
Obit=CODE(0x1bbf074) has died.
Obit=SCALAR(0x1bb50d4) (Greetings) has died.
$g is no more.

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        - tye (but my friends call me "Tye")

In reply to (tye)Re: Closures and scope by tye
in thread Closures and scope by nop

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