(jeffa) Re: Why are closures cool, continued?

If you wanted a 'real' constructor, just add bless:

sub new {
   my ($class, @stuff) = @_;
   return bless sub { doit(@stuff, @_) },$class;
}

Now, if you want what i consider to be a good, everyday, pratical solution that uses a closure (not just a crazy way to make eyes go cross-eyed), then check out (the recently renamed) (jeffa) Practical Use For What jeffa Thought A Closure Was (3Re: Style Question on Closures). There are, of course, many more practical uses for closures ... this one has served me well, and i really think that it is easy to understand.

UPDATE: nope - i am wrong again. Sorry mr.dunstan. Thanks for the catch perrin.

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

[perrin]

That's a good example of using code refs, but it's not a closure. There are no private variables (unless I missed something there).

[dws]

That's a good example of using code refs, but it's not a closure. There are no private variables (unless I missed something there).

The anonymous routine (blessed or not) refers to a lexically-scoped variable in its enclosing scope. That lexically-scoped variable is magically kept alive (in the anonymous subroutine) after that enclosing scope has been exited. That is what makes an anonymous subroutine a closure.

sub makeAnonymousSub {
    sub { print "I am not a closure\n" }
}

sub makeClosure {
    my $x = shift;
    sub { print "I keep $x alive, thus I'm a closure\n" }
}


Update: This is in agreement with perrin, btw. I'm just filling in some details...

[perrin]

Are we looking at the same thing? The example jeffa posted has this anonymous routine in it:

print $foo->print_me(sub {ucfirst shift}), "\n";

It's not a closure.

[mr.dunstan]

Hey! I was thinking something along those lines, just because the variables themselves are not declared -within- the closure ... only near it?

I am thinking this means:
1) There is no spoon, I mean closure.
2) That's a closure, but not an academic example of a closure.
3) Mr. Dunstan, you are mincing words to gain karma.

Zuh? -mr.dunstan

[perrin]

Sort of. To make a closure, you have to refer to lexical variables that are declared outside of the scope of the current sub. That's the definition of a closure.