increasing value every time sub routine called

bigmoose has asked for the wisdom of the Perl Monks concerning the following question:

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Re: increasing value every time sub routine called by BrowserUk (Patriarch) on Dec 09, 2011 at 12:39 UTC
`sub increaseNumber { my $value = 001 return $value + 1 };` [download] Every time you call that sub, you (re)set `$value` to one. If you did it this way: `my $value = 1; sub increaseNumber { return ++$value; };` [download] It would work as you want. Why post pseudo-code rather than proper Perl? With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. The start of some sanity?	[reply] [d/l] [select]
Re^2: increasing value every time sub routine called by bigmoose (Acolyte) on Dec 09, 2011 at 12:49 UTC
I worked it out :) `increase(); increase(); increase(); sub increase { $n += 1; # Global variable $n print "$n\n"; }` [download]	[reply] [d/l]
Re: increasing value every time sub routine called by Fox (Pilgrim) on Dec 09, 2011 at 12:48 UTC
well, if you really want to do this: `use feature "state"; sub a { state $i++; print $i; } a(); a(); a();` [download] prints 123	[reply] [d/l]
Re: increasing value every time sub routine called by johngg (Canon) on Dec 09, 2011 at 16:22 UTC
Have a look at sprintf for your leading zeros. Others have mentioned closures or subroutines incrementing a global variable. IMHO a closure is tidier, obviating the need for a global that might accidentally get tinkered with elsewhere in the code. `knoppix@Microknoppix:~$ perl -Mstrict -wE ' > my $rcIncrement = do { > my $value = 0; > sub { return sprintf q{%03d}, ++ $value }; > }; > > say $rcIncrement->() for 1 .. 3; > say q{-} x 10; > say $rcIncrement->() for 1 .. 3;' 001 002 003 ---------- 004 005 006 knoppix@Microknoppix:~$` [download] I hope this is helpful. Cheers, JohnGG	[reply] [d/l]
Re: increasing value every time sub routine called by jethro (Monsignor) on Dec 09, 2011 at 12:56 UTC
the concept you are looking for is called a closure	[reply]
Re^2: increasing value every time sub routine called by JavaFan (Canon) on Dec 09, 2011 at 14:07 UTC
No, he doesn't. He isn't asking for multiple instances of counters. A single subroutine with an external variable (or an internal state variable) will do. `sub next_number {no warnings;++$::N} say next_number; say next_number; say next_number; __END__ 1 2 3` [download]	[reply] [d/l]
Re^3: increasing value every time sub routine called by dave_the_m (Monsignor) on Dec 09, 2011 at 15:33 UTC
Well in perl land, a single (named) subroutine with a (lexical) external variable is still classed as a closure. Dave.	[reply]
Re^4: increasing value every time sub routine called by JavaFan (Canon) on Dec 09, 2011 at 21:50 UTC
Re: increasing value every time sub routine called by TJPride (Pilgrim) on Dec 09, 2011 at 19:16 UTC
Just keep in mind that the variable declaration only happens if you call the sub after it's been declared, so you either need to "use" the function or call it from below, like in my example: `use strict; use warnings; { my $persistent = 0; sub increment { print ++$persistent; }} increment(); increment(); increment();` [download]	[reply] [d/l]