Re: Closures clarification

If I'm not mistaken, neither of your examples are closures. According to Intermediate Perl, a closure is "just a subroutine that references a lexical variable that has gone out of scope".

In your first example, while there is an anonymous subroutine reference passed to the find() function, it doesn't reference any lexical variables. In your second example, 1) there is no subroutine, and 2) the $a enclosed in braces is a different variable than the one outside of them.

Note also that your first example was incorrect. It should have been:

use File::Find;

my $total_size = 0;
find(sub {$total_size += -s if -f}, '.');
print $total_size, "\n";
[download]

You were missing the "use" statement, missing a "(" in the find function, and the "{" in the sub definition was misplaced.

An example of a closure from Intermediate Perl) is as follows:

use File::Find;
my $callback;
{
  my $count = 0;
  $callback = sub { print ++$count, ":$File::Find::name\n" };
}
find($callback, '.');
[download]

So, here the subroutine is a closure because it refers to the lexical variable $count.

Hope this helps.

memnoch

Gloria in Excelsis Deo!

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Re^2: Closures clarification by lodin (Hermit) on Dec 04, 2007 at 14:52 UTC
If I'm not mistaken, neither of your examples are closures. According to Intermediate Perl, a closure is "just a subroutine that references a lexical variable that has gone out of scope". The anonymous subroutine passed by reference to `find` does bind a lexical variable (`$total_size`). By most definitions (e.g wikipedia's), that subroutine is then a closure. The variable doesn't have to have gone out of lexical scope. The important part is that the subroutine deeply binds the variable, and the variable may go out of scope. lodin PS. The code should read `sub {` instead of `{ sub`, but that's not important for the question at hand.	[reply] [d/l] [select]
Re^3: Closures clarification by memnoch (Scribe) on Dec 04, 2007 at 15:52 UTC
Thanks lodin...I missed that other typo! I have addressed it in my previous posting. But as far as whether it was a closure or not, according to Intermediate Perl, the lexical variable needs to have gone out of scope for the subroutine to be a closure....that's what I was going off of. memnoch *Gloria in Excelsis Deo!*	[reply]
Re^2: Closures clarification by fenLisesi (Priest) on Dec 04, 2007 at 14:11 UTC
And what else is he missing? `use File::Find; my $total_size = 0; find({sub $total_size += -s if -f}, '.'); print $total_size, "\n";` [download] You were missing the "use" statement and a "(" in the find function.	[reply] [d/l]
Re^3: Closures clarification by memnoch (Scribe) on Dec 04, 2007 at 16:35 UTC
Thanks fenLisesi....I missed that other typo...I have fixed it in my original posting as well. memnoch *Gloria in Excelsis Deo!*	[reply] [d/l]