Re^2: How do closures and variable scope (my,our,local) interact in perl?

Could you please give an example? IMHO closures mean exactly the contrary of what I understand you saying.

The problem here is that ELISHEVA is adding to the very different concepts of package vs lexical variables the dark forces of for-loops creating local aliases interfering differently with compile-time and run-time behavior of local variables.

Cheers Rolf

UPDATE: OK, I think the source of misunderstandings is what people mean when they say "closure". Do you mean the outer or the inner sub/block ?

Comment on Re^2: How do closures and variable scope (my,our,local) interact in perl?

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Re^3: How do closures and variable scope (my,our,local) interact in perl? by Zarchne (Novice) on Jun 19, 2009 at 21:47 UTC
Perhaps I'm being too simple-minded, but please consider this variant: `use strict qw(vars subs); my $name; { my $name = 'red'; $name = sub { "<FONT COLOR='$name'>@_</FONT>" }; } { my $name = 'blue'; $name = sub { "<FONT COLOR='$name'>@_</FONT>" }; } $name = '<none>'; print red(), "\n"; print blue(), "\n"; __END__ <FONT COLOR='red'></FONT> <FONT COLOR='blue'></FONT>` [download] Without the additional block delimiters (`{}`) and `my` declarations, the variable `$name` indeed always refers to the same storage (which, I admit, was not clear in my own mind when I wrote the above comment). Closures (`red()` and `blue()` here) only get a copy of a portion of their lexical environment (that is, become "closures", properly so-called) when they escape a region where that portion is (lexically, of course) in scope. Without a block that the thread of execution leaves, no closure is created and the code is indistinguishable from a regular sub. Note that `red()` and `blue()` (i.e. `&red` and `&blue`) exist outside the blocks because they are created in the package's (here, main) symbol table -- as using a type glob (``) always implies. Here's the code with another wrinkle to illustrate: `use strict qw(vars subs); { my $name; { my $name = 'red'; $name = sub { "<FONT COLOR='$name'>@_</FONT>" }; } { my $name = 'blue'; $name = sub { "<FONT COLOR='$name'>@_</FONT>" }; } foo = sub { print red($name), "\n"; print blue($name), "\n"; }; $name = 'another wrinkle'; } foo(); print red('hi mom'); __END__ <FONT COLOR='red'>another wrinkle</FONT> <FONT COLOR='blue'>another wrinkle</FONT> <FONT COLOR='red'>hi mom</FONT>` [download]	[reply] [d/l] [select]

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Re^3: How do closures and variable scope (my,our,local) interact in perl?
by Zarchne (Novice) on Jun 19, 2009 at 21:47 UTC

use strict qw(vars subs);
my $name;

{
    my $name = 'red';
    *$name = sub { "<FONT COLOR='$name'>@_</FONT>" };
}

{
    my $name = 'blue';
    *$name = sub { "<FONT COLOR='$name'>@_</FONT>" };
}

$name = '<none>';

print red(), "\n";
print blue(), "\n";
__END__
<FONT COLOR='red'></FONT>
<FONT COLOR='blue'></FONT>
[download]

{}

my

$name

red()

blue()

become

closure

red()

blue()

&red

&blue

*

 use strict qw(vars subs);

{
    my $name;

    {   my $name = 'red';
        *$name = sub { "<FONT COLOR='$name'>@_</FONT>" }; }
    {   my $name = 'blue';
        *$name = sub { "<FONT COLOR='$name'>@_</FONT>" }; }

    *foo = sub {
        print red($name), "\n";
        print blue($name), "\n";
    };

    $name = 'another wrinkle';
}

foo();
print red('hi mom');

__END__
<FONT COLOR='red'>another wrinkle</FONT>
<FONT COLOR='blue'>another wrinkle</FONT>
<FONT COLOR='red'>hi mom</FONT>
[download]

[reply]
[d/l]
[select]