problems with the "switch" module

mrguy123 has asked for the wisdom of the Perl Monks concerning the following question:

Hi monks
I have been using the switch module in several Perl programs without any trouble...until now.
One of my programs that wasn't working properly was fixed by changing the switch to if and elesif. Since the program is very long and consists of several files that inherit from each other, this is just the switch code:

switch($proxy_type){
        case 'SQUID' {
            $web_proxy = $proxy_address;
        }
        case 'EZPROXY' {
            if ($proxy_credentials){
                ($user_name, $password) =
                split /\//, $proxy_credentials;
                $prefix =
                $proxy_address."user=$user_name&pass=$password&url="
;   
            }
            else {
                $prefix = $proxy_address."url=";
            }
        }
    }
[download]

What the code does is not very important, but the fact is that when I change the switch to "if" and comment out the "use switch" line, the program works. I have used switches in other programs, and would like to know what is the cause of this problem, and where and when it might apear again? Any ideas?
Thanks, Guy Naamati (mrguy123)

A truth that's told in bad intent beats all the lies you can invent

Comment on problems with the "switch" module Download Code

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Re: problems with the "switch" module by Fletch (Bishop) on Jul 10, 2006 at 15:22 UTC
I believe the current wisdom regarding using Switch is "Don't". See Categorized Damian Modules for the warning straight from the horse's mouth.	[reply]
Re^2: problems with the "switch" module by mrguy123 (Hermit) on Jul 11, 2006 at 06:38 UTC
Thanks for the advice. I guess it would have been better if I had known about Categorized Damian Modules before I released programs with Switch to customers :( , but better late than never.	[reply]
Re: problems with the "switch" module by Zaxo (Archbishop) on Jul 10, 2006 at 17:07 UTC
Your use for Switch.pm could be done as well with a dispatch table. That is a hash of code references, like so, `my %dispatch = ( SQUID => sub { $web_proxy = $proxy_address; }, EZPROXY => sub { if ($proxy_credentials){ ($user_name, $password) = split /\//, $proxy_credentials; $prefix = $proxy_address."user=$user_name&pass=$password& +url="; } else { $prefix = $proxy_address."url="; } } ); $dispatch{$proxy_type}->();` [download] Your functions should take arguments and return values, rather than modifying global variables, but I didn't know enough about your app to change that. CountZero++ is right, repaired. Paste confusion. After Compline, Zaxo	[reply] [d/l]
Re^2: problems with the "switch" module by CountZero (Bishop) on Jul 10, 2006 at 18:20 UTC
I think the `$prefix = $proxy_address."url=";` is part of the `EZPROXY` case, so it should go into the `EZPROXY` sub. CountZero "If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law	[reply] [d/l] [select]
Re: problems with the "switch" module by planetscape (Chancellor) on Jul 10, 2006 at 17:34 UTC
Please see our Tutorials page, where you can find Implementing Dispatch Tables, if you desire more information on Zaxo's solution. HTH, planetscape	[reply]
Re: problems with the "switch" module by kwaping (Priest) on Jul 10, 2006 at 15:23 UTC
I recommend doing a SuperSearch on switch.pm. There are quite a few discussions about problems with this module. --- It's all fine and dandy until someone has to look at the code.	[reply]
Re: problems with the "switch" module by pjf (Curate) on Jul 11, 2006 at 00:29 UTC
G'day Guy, `Switch` uses source-filters in order to make your code do its job. Most of the time it gets it right, but sometimes it will twist the code that reaches the Perl in unexpected ways, and that can make debugging very challenging. If you're getting very strange errors due to using Switch, there's a good chance that the source-filter may have adjusted your code incorrectly. The good news is that Perl 5.10 (not yet released) has a Switch-style construct that's built into the language. It's called `given`, and looks very similar to its Perl 6 counterpart. You can find more information in one of the recent development deltas. Paul Fenwick Perl Training Australia	[reply]