Re^2: Lost anonymous subs

[kappa]

I have written almost exactly the same piece of code in the reply to diotalevi up there because did not spot your comment. Yes, that helped me to understand things.

I somehow got thinking that closures copy referenced lexicals when created. That was my error.

This is the case when copying really takes place:

my $Big = 'X' x 1000000;
sub big {
    my $big = $Big;
    return sub { $big };
}
my @crefs;
push @crefs, big() for 1..10;

[diotalevi]

Well yes, that's because the = operator copies stuff. There's nothing special about that.

[kappa]

my @abc;
for my $m qw/a b c/ {
    push @abc, sub { $m };
}
print $_->() . "\n" for @abc;

No assignments and still, those subs each has its own $m. Or does the for my $m creates a new variable on each iteration?

[diotalevi]

The my() operator has a runtime effect of creating a new variable so each time you start that loop, you have a new variable to have potentially bound to. This also works if you write code like this.

my @abc;
for my $m ( qw/a b c/ ) {
    push @abc, \ $m;
}
print @abc

[ysth]

Not exactly copy, more just steal. Usually lexicals hang around for the next time they go into scope (though they get reset to be empty/undef, they still hold memory). If you take a reference to one (including the case of a closure) and hold the reference until the lexical goes out of scope, the lexical has to get reallocated, since the remaining reference keeps the original.