Re^2: Passing anon sub as param

(1) To make traverse reusable. You can change the action taken for every node without editing traverse. You can make traverse do two different things without writing two different versions of it.

Hence, I could have done the following just as well --

sub traverse {
  # do yer stuff
  _print($_);
  traverse(..);
}

sub _print {
  my ($node) = @_;
  print ' ' x $node->{dept}, $node->{c_id}, ': ', $_->{comm}, "\n";
}
[download]

Which, I did, and it also works. Hence, passing an anon sub as a param seems to be just ~~a fancy way of doing what I already know~~ MTOWODI, no?

--

when small people start casting long shadows, it is time to go to bed

Comment on Re^2: Passing anon sub as param Download Code

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Re^3: Passing anon sub as param by fishbot_v2 (Chaplain) on Jul 28, 2005 at 20:54 UTC
I personally think that the anon-sub call back is just cleaner looking, but it has a number of other benefits. The biggest of those is that it doesn't break or force you to do ugly things if `traverse` is in another package. Other benefits: you don't clutter up your symbol table with global named functions that are only intended to be used in one place. Also: you can use `traverse` in different ways in the same application, rather than defining the callback globally. I also think that defining a fallback is cleaner in this case: you just check the `$code` arg for definedness, rather than probing the caller's package. Scope is nice and closed.	[reply] [d/l] [select]
Re^3: Passing anon sub as param by ikegami (Patriarch) on Jul 28, 2005 at 20:56 UTC
How about I explain by example: `traverse($in, 0, 0, sub {print ' ' x $_->{dept},'-',$_->{comm},"\n";}) +; ... later in the code... traverse($in, 0, 0, sub {$sth->execute($dept, $comm)});` [download] By the way, the sub doesn't have to be anon: `sub _print { print ' ' x $_->{dept},'-',$_->{comm},"\n"; } traverse($in, 0, 0, \&_print);` [download] It's a feature, it has no side effects, so there's no reason to get rid of it, and there's every reason to keep it. If you don't want to explicitely specify it, create a wrapper: `sub print_tree { push(@_, 0, 0, sub {print ' ' x $_->{dept},'-',$_->{comm},"\n";}); &traverse; } print_tree($in);` [download]	[reply] [d/l] [select]
Re^3: Passing anon sub as param by GrandFather (Saint) on Jul 28, 2005 at 20:52 UTC
Passing an action in allows the parent node to determine the action rather than the local node determining the action. Perl is Huffman encoded by design.	[reply]