Curious corner cases concerning closure cloning

[Luke Palmer]

What do these do?

 for 1,2 {
 my $code = {
 my $x;
 BEGIN { $x = 42 }
 $x;
 };
 say $code();
 }

 for 1,2 {
 my $code = {
 state $x;
 BEGIN { $x = 42 }  # mind you, not FIRST
 $x++;
 };
 say $code();
 say $code();
 }

 for 1,2 - $x {
 END { say $x }
 }

Thanks,
Luke

Re: Curious corner cases concerning closure cloning

[Yuval Kogman]

On Mon, Aug 14, 2006 at 16:01:47 +, Luke Palmer wrote:
 What do these do?

Intuition based answers:

  for 1,2 {
  my $code = {
  my $x;
  BEGIN { $x = 42 }
  $x;
  };
  say $code();
  }

I think the closure would be emitted equivalently to my $x = 42, or
perhaps $x is not in the BEGIN blocks scope at all.

  for 1,2 {
  my $code = {
  state $x;
  BEGIN { $x = 42 }  # mind you, not FIRST
  $x++;
  };
  say $code();
  say $code();
  }

Again, assuming the BEGIN { } body is not even compile but it's side
effect is meaningful, this is the same as 

state $x = 42;

but starting to get a little tougher to justify.

Perhaps it does that, but also emits a warning e.g. 'implicit
initial value for future-scoped lexical' or something like that.


  for 1,2 - $x {
  END { say $x }
  }

undef, because END is like a declaration putting the closure in some
global, and doesn't actually happen at runtime.

Otoh

for 1,2 - $x {
state $y = $x;
END { say $y }
}

Might work

-- 
  Yuval Kogman [EMAIL PROTECTED]
http://nothingmuch.woobling.org  0xEBD27418



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Re: Curious corner cases concerning closure cloning

[Jonathan Scott Duff]

On Mon, Aug 14, 2006 at 04:01:47PM +, Luke Palmer wrote:
 What do these do?
 
  for 1,2 {
  my $code = {
  my $x;
  BEGIN { $x = 42 }
  $x;
  };
  say $code();
  }

Assuming that variables are available immediately as
they are parsed and that BEGIN blocks disappear as soon as they
execute, I'd expect that the first $code would be equivalent to 

my $code = { my $x = 42; $x; };

and the second code would be equivalent to

my $code = { my $x ; $x; };

So, I guess the output would be 

42
# this line intentionally left blank  :-)


  for 1,2 {
  my $code = {
  state $x;
  BEGIN { $x = 42 }  # mind you, not FIRST
  $x++;
  };
  say $code();
  say $code();
  }

Same thing here, except because it's a state variable, it keeps it's
value between invocations, so the output would be:

42
43
# again, blank on purpose
1

  for 1,2 - $x {
  END { say $x }
  }

For this one I'd guess that a solitary 2 is output.  The END block
closed over the $x and the last value that $x obtained was 2.

my humble guesses,

-Scott
-- 
Jonathan Scott Duff
[EMAIL PROTECTED]