Appending to variable with a switch statement?

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() }
    ...
}
[download]

...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

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Comment on Appending to variable with a switch statement? Download Code

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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.	[reply] [d/l]
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') ) : ( $_ eq ... ) ? ( ... ) : ( ... test ... ) ? ( ... then ... ) : ( final 'else' value )` [download] Without seeing more of what you're trying to do, I'd think you should probably look at using a lookup table. (see super search for more details on lookup tables, if you're not familiar with them)	[reply] [d/l]
Re: Appending to variable with a switch statement? by diotalevi (Canon) on Jan 06, 2007 at 21:26 UTC
There is no perlish switch statement. If you're using Switch then you're asking for a house to drop onto your head. ⠤⠤ ⠙⠊⠕⠞⠁⠇⠑⠧⠊	[reply]
Re: Appending to variable with a switch statement? by Joost (Canon) on Jan 06, 2007 at 21:26 UTC
Since you don't care about what's in %A, you don't really need a case statement. `$responseXML .= sloven('xml') for keys %A;` [download] or even `$responseXML .= ( sloven('xml') x scalar keys %A);` [download] if sloven('xml') has no side effects. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l] [select]


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