Re^2: Lexical closures

[spurperl]

in reply to Re: Lexical closures
in thread Lexical closures

So let me see if I get this correctly... Perl's foreach creates a new lexical scope (i.e. a new binding a.k.a. stack frame) at each iteration.

Python's for loop doesn't do that, and hence the difference in behavior.

Does Perl's for (my $i = 0; $i < $N; ++$i) behave the same way?

I wonder about the tradeoffs here. It seems likely that foreach's creation of new scopes cost something. Does it make it inherenty slower than a for loop that would not create a scope ?

[GrandFather]

No. The confusion is that Perl effectively closes over the value of the variable, not a reference to the variable.

All languages that I know where you can declare a variable locally to the scope of a block (including a block for a loop) effectively set up a new stack frame on each entry to the block, but the loop variable is outside that block or it couldn't maintain its contents from one iteration to the next.

[JavaFan]

The confusion is that Perl effectively closes over the value of the variable, not a reference to the variable.

sub make_funcs {
    my $val = shift;
   (sub {$val * $val},
    sub {$val++})
}

my($f3, $i3) = make_funcs(3);  
my($f5, $i5) = make_funcs(5);  

say $f3->();  
say $f5->();  
$i3->();  
say $f3->();  
say $f5->();  

__END__
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I can't explain my results in combination with your claim.