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

Greetings, Fellow Monks.

I'm working on something that involves using a switch() statement to call different subroutines based on the values inside a hash. Here is what the code looks like: 

use Switch;
switch(%A) {
    case 'sloven' { $responseXML .= sloven('xml') }
    case 'leggert' { $responseXML .= wiggedy() }
    ...
}

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...And so on. This is all well and good, but in every single case, I'm appending to $responseXML. In keeping with the Perlish quality of laziness, is there a way to append to $responseXML in every case, without having to type it every time?

Thanks,
Spidy
My Website
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Replies are listed 'Best First'.
Re: Appending to variable with a switch statement?
by jbert (Priest) on Jan 06, 2007 at 21:39 UTC
    As noted elsewhere, there isn't really a switch statement in perl.

    You can get a nice effect though - and also answer your question about removing the repeated bit of code - by using a dispatch table. Perl has the nice feature of anonymous subroutines/closures, which allow you to write a snippet of code in the middle of another function. These snippets are scalars (since they are references) and so can be stored anywhere you can normally store a scalar, in particular as a hash value.

    So you can do things like: 

    my %dispatch_table = (
  sloven => sub { return sloven('xml'); },
  badger => sub { return badger2xml(); },
);


my $case = 'sloven';
my $subref = $dispatch_table{$case};
$responseXML .= $subref->();

    [download]
    Your code snippets can take arguments (which you'd put in place of the dots in the ->(...) call) and access them in the normal with via @_. They can also do anything code can do (including random sideeffects) rather than just returning a value as above.

    All in all, a cool and useful technique.

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Re: Appending to variable with a switch statement?
by jhourcle (Prior) on Jan 06, 2007 at 21:40 UTC
    is there a way to append to $responseXML in every case, without having to type it every time?

    You may wish to use a construct that's composed of '? :', which avoids the use of 'Switch', but I'm not sure if it's more lazy, as it requires some extra typing:

    $responseXML .= 
     ( $_ eq 'sloven' ) ? ( sloven('xml') )
   : ( $_ eq ... )      ? ( ... )
   : ( ... test ... )   ? ( ... then ... )
   :                      ( final 'else' value )

    [download]

    Without seeing more of what you're trying to do, I'd think you should probably look at using a lookup table. (see super search for more details on lookup tables, if you're not familiar with them)

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Re: Appending to variable with a switch statement?
by diotalevi (Canon) on Jan 06, 2007 at 21:26 UTC

    There is no perlish switch statement. If you're using Switch then you're asking for a house to drop onto your head.

    ⠤⠤ ⠙⠊⠕⠞⠁⠇⠑⠧⠊

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Re: Appending to variable with a switch statement?
by Joost (Canon) on Jan 06, 2007 at 21:26 UTC
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