Re: How to access a variable inside subroutine?

As an alternative to the state keyword for turning your subroutine into a coroutine (a function that maintains state between calls), here is how you use a closure to effectively maintain a state variable declared outside of the counter subroutine and provides access to the current value of $add via subroutine "getter". In this way, $add is read only and only affected via counter. The ADD_COUNTER_CLOSURE: is simply a label handy in this case for self documenting the existence of the closure itself.

ADD_COUNTER_CLOSURE:
{
  # $add is not accessible outside of closure, but
  # you do the 'getter', "add" which has access to $add
  my $add = 0;
  sub counter {
    my @nums = (1..500); 
    for my $num(@nums) { $add += $num }
  }
  
  # getter
  sub add {
    return $add;
  }
}

# $add is not accessible directly here, must use add subroutine

my $add = add;
print qq{$add\n};

# increment $add via closure()
counter();
$add = add;
print qq{$add\n};
[download]

Output:

0
125250
[download]

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Re^2: How to access a variable inside subroutine? by pryrt (Abbot) on Sep 05, 2020 at 20:43 UTC
I had an idea when you used the pre-state closure idea: put your getter inside the context of `counter`, so it that `$add` is in scope: `use 5.030; use strict; use warnings; sub counter { my @nums = (1..500); state $add = 0; for my $num (@nums) { $add += $num; } sub getter { $add } # because this sub is inside the scope of coun +ter(), it has visibility on $add! } counter(); say "getter => ", getter();` [download]	[reply] [d/l] [select]
Re^3: How to access a variable inside subroutine? by Fletch (Bishop) on Sep 06, 2020 at 05:10 UTC
Side note: be careful doing this with a `my` variable because some weird things can happen with nested subs referencing lexicals from the enclosing scope. Look for `Variable "%s" will not stay shared` in perldiag. The cake is a lie. The cake is a lie. The cake is a lie.	[reply] [d/l] [select]
Re^4: How to access a variable inside subroutine? by LanX (Saint) on Sep 06, 2020 at 05:55 UTC
I wanted to give the same warning and I'm not sure this is less of a problem with `state` Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply]
Re^5: How to access a variable inside subroutine? by tobyink (Canon) on Sep 06, 2020 at 09:04 UTC
Re^6: How to access a variable inside subroutine? by LanX (Saint) on Sep 06, 2020 at 09:42 UTC
Some notes below your chosen depth have not been shown here
Re^3: How to access a variable inside subroutine? by pritesh_ugrankar (Monk) on Sep 05, 2020 at 21:08 UTC
Hi, Thank you!! It worked!!....I have always been baffled by the "getter/setter" stuff...I still don't understand it, but still was able to run the code you wrote.	[reply] [d/l] [select]
Re^4: How to access a variable inside subroutine? by Anonymous Monk on Sep 06, 2020 at 22:37 UTC
Generically speaking, "getters and setters" are any routine that you can (must ...) call to affect a value that you can't access directly – because it is inside of a closure or an object. In the general sense, they often have "side effects." For instance, calling a "color setter" actually causes the color of something to change, and also completely conceals the mechanics of how that actually happens.	[reply]
Re^3: How to access a variable inside subroutine? by perlfan (Parson) on Sep 05, 2020 at 20:51 UTC
Very nice, thank you. I was going old school but now this is a lot cleaner and more concise.	[reply]
Re^4: How to access a variable inside subroutine? by perlfan (Parson) on Sep 05, 2020 at 21:20 UTC
Read the link pointed out by LanX. Best way to learn it is to play around with it. Oops replied to the wrong thing. pritesh_ugrankar this message applies to your comment about it now working but you not understanding.	[reply]