On Fri, Oct 15, 2010 at 11:40 PM, Owen Chavez <owen.chavez314...@gmail.com> wrote: > I've started experimenting with the use of subroutines in place of large, > repeating blocks of code in a few of my programs. Without exception, these > subroutines require variables defined outside of the subroutine. Unless I'm > mistaken, the only way to make these variables available within the > subroutine is to define them as global variables using "our."
You, good sir, are mistaken. :) Globals are very rarely /required/. Subroutines accept arguments for a reason. Not only does it make them reusable for different sources of data, but it also restricts their influence over the program. Global variables are accessible by the entire program. Even file scope[1] variables are accessible by an entire file! That means that you have a lot more chances to make a mistake that causes a bug that makes the code do the wrong thing. `my` is your friend in this regard. Basically no matter which programming language you are using you typically want to avoid global scope whenever you can. Take an hour out of your life to watch the following video (even if you don't understand it right away): http://www.youtube.com/watch?v=-FRm3VPhseI It's somewhat Java-centric, but it applies to basically all programming languages. The more code that is allowed to access a given piece of data the more likely that the program is to incorrectly manipulate that data. The code is written by people and people are fallible. In Perl, arguments can be passed to your own custom subroutines the same way that they are passed to built-in subroutines. As comma-separated lists, "optionally" enclosed in parenthesis. For example: #!/usr/bin/env perl use strict; use warnings; # Passes "foo", "bar", "baz", and "\n" to print. print "foo", "bar", "baz", "\n"; # Same as above. print("foo", "bar", "baz", "\n"); sub print_sum { my ($a, $b) = @_; print($a + $b, "\n"); } # Passes 5 and 10 to print_sum. print_sum 5, 10; # Same as above. print_sum(5, 10); my $lhs = 5; my $rhs = 10; # Passes the values of $lhs and $rhs to print_sum. # Effectively, the same as above. print_sum($lhs, $rhs); __END__ Argument passing allows you to limit /scope/, which is very important for reliable coding. It can be acceptable to use global variables for simple scripts, but if you're writing non-trivial programs then you should probably avoid global /state/ and try to limit scope as much as possible. [1] http://en.wikipedia.org/wiki/Scope_(programming) -- Brandon McCaig <bamcc...@gmail.com> V zrna gur orfg jvgu jung V fnl. Vg qbrfa'g nyjnlf fbhaq gung jnl. Castopulence Software <http://www.castopulence.org/> <bamcc...@castopulence.org> -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
