SPUG: It gaugtht bettuh...

[Dave Olszewski]

On Fri, 8 Jul 2016, Mark Hinds wrote:

> Dyck, David wrote:
> > It's been a while since I read
> >     http://perldoc.perl.org/perlref.html#Function-Templates
> > 
> > Did you see this note at the bottom:
> >     CAVEAT: Aliasing does not work correctly with closures. If you try to
> > alias lexical variables from an inner subroutine or eval, the aliasing will
> > only be visible within that inner sub, and will not affect the outer
> > subroutine where the variables are declared. This bizarre behavior is
> > subject to change.
> 
> Hi Dave,
> 
> Interesting, but I'd never even think use such a construct. Even if I did
> want to create a local function it could simply put it into a simple
> my variable and all would be well, no?
> 
> HandleEvent(SomeEvent, sub {
>     my $x = $_[0] + 23;
>     my $localFunc = sub { return $x *2 };
>     return $localFunc->();
> });

I haven't experienced this as it relates to a pretty new feature of Perl
(lvalue references), but it sounds more nuanced

  sub foo {
      my $x = 1;
      my $bar = sub {
          \(my $y) = \($x);
          $y = 3;
      }

      return $bar;
  }

so in that case, the $x in the returned closure would be aliased and
modified by the assignment to $y, but the outer closed-over $x is not
affected.

> 
> 
> 
> 
> 
> 
> > -----Original Message-----
> > From: spug-list [mailto:spug-list-bounces+david.dyck=fluke.com at pm.org] On
> > Behalf Of Mark Hinds
> > Sent: Thursday, July 7, 2016 7:06 AM
> > To: SPUG Members <spug-list at pm.org>
> > Subject: SPUG: It gaugtht bettuh...
> > 
> > 
> > OK, it looks like this list isn't quite dead yet... :-)
> > 
> > I've been using perl since sometime back in the 90's.
> > 
> > I ended up using it in an embedded linux system about 10 years ago
> > to replace a guile based scripting engine - That's one ugly M...
> > 
> > I used mod Event to create a pure event system to handle bunches of
> > serial IO and timer events. Worked/works great. Perl is a quite
> > a CPU big, but still compares well with other dynamic languages.
> > 
> > Seems that Python has taken over from Perl these days. I never liked
> > Python - using indention as fundamental element of syntax is obnoxious -
> > IMHO.
> > 
> > I suppose Perl's goofy syntax make people cringe - I find it a rather
> > charming idiosyncrasy myself :-)
> > 
> > Question - Perl's anonymous functions seem to operate perfectly well
> > as closures - they capture the referenced environment properly and
> > free it when they themselves are no longer referenced. The guile
> > folks disputed that me those many years ago. Thoughts?
> > 
> > 
> > 
> > 
> > 
> > 
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> > 
> 
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>