Re: Iterator to parse multiline string with \\n terminator

[Laurent_R]

Hi,

as a side note, your anonymous function does not really act as a closure:

my $fh = IO::File->new($filename, 'r');

my $fh_iterator = sub {
    my $fh = shift;

    my $line = $fh->getline;
}

while (my $line = $fh_iterator->($fh)) {
    # do stuff to $line
}

because you are passing $fh each time to the sub (and you have to, you actually get a fresh copy of $fh each time the anonymous subroutine is called).

If you want it to act as a closure, you may do something like this (untested):

sub create_iterator{
   my $filename = shift;
   my $fh = IO::File->new($filename, 'r');
   return sub { 
      my $line = $fh->getline;
   }
}

my $fh_iterator = create_iterator($file_name);

while (my $line = $fh_iterator->()) {
    # do stuff to $line
}

Now, $fh is really a persistent variable within the sub scope, this is a real closure.

[three18ti]

What exactly makes it not a closure? Is it that I'm passing a variable each time? If it was a new copy of $fh, wouldn't $fh_iterator->($fh) always return the same line (since it's creating a copy of the $fh object, on next passing it would be a copy of the original)?

Thanks for setting me straight, I always like learning new things.

[Laurent_R]

$fh is a file handler, i.e. it is actually an iterator on a file, so that each time you read from $fh, you get the next line. In your sub, your my $fh = shift; actually creates a new copy of $fh each time the sub is called. It still works because $fh "knows" which is the next line to read from the file. But your anonymous sub is not a closure; the alternative code I wrote is actually keeping its own copy of $fh, my anonymous sub actually closes on $fh. Please note that an anonymous function is not necessarily a closure, and a closure does not necessarily have to be anonymous (although is is often the case).

You might want to have a look to this: Closure on Closures.

[three18ti]

Awesome! Thanks for the info and link.