Switch.pm makes code look elegant, but imposes significant performance penalty. I learnt this the hard way. Here is the lesson, hopefully it should help others.

Using Switch:

$ cat switch.pl
#!/usr/local/bin/perl

use Switch;

my $letter = "c";
switch($letter) {
        case "a" {print "1"}
        case "b" {print "2"}
        case "c" {print "3"}
}
[download]

Profiling this program with Devel::NYTProf, gave some valuable insight:

 ______Source_Code_Files_—_ordered_by_exclusive_time_then_name__
+_____
|Stmts|Exclusive|Reports           |Source File                       
+     |
|_____|Time_____|__________________|__________________________________
+_____|
|3508_|324ms____|line • block |Text/Balanced.pm_______________________
+|
|542__|147ms____|line • block |Switch.pm______________________________
+|
|77___|32.1ms___|line • block |Exporter/Heavy.pm______________________
+|
|52___|31.7ms___|line • block |Config_heavy.pl________________________
+|
|132__|30.9ms___|line • block |warnings/register.pm___________________
+|
|73___|22.2ms___|line • block |DynaLoader.pm__________________________
+|
|39___|29.2ms___|line • block |SelfLoader.pm_(including_1_string_eval)
+|
|27___|15.5ms___|line • block |AutoLoader.pm__________________________
+|
|184__|13.3ms___|line • block |overload.pm____________________________
+|
|83___|12.9ms___|line • block |vars.pm________________________________
+|
|170__|12.2ms___|line • block |Exporter.pm____________________________
+|
|40___|10.4ms___|line • block |Config.pm______________________________
+|
|12___|9.38ms___|line • block |Carp.pm________________________________
+|
|25___|7.80ms___|line • block |Filter/Util/Call.pm____________________
+|
|15___|7.77ms___|line • block |switch.pl______________________________
+|
|25___|6.78ms___|line • block |version.pm_____________________________
+|
|123__|4.36ms___|line • block |strict.pm______________________________
+|
|34___|2.22ms___|line • block |warnings.pm____________________________
+|
|26___|619µs___|line • block |feature.pm_____________________________|
|1____|8µs_____|line • block |Config_git.pl__________________________|
|5188_|720ms____|Total_(-4_statements_are_unaccounted_for)____________
+_____|
|259__|36.0ms___|Average______________________________________________
+_____|
|_____|12.9ms___|Median_______________________________________________
+_____|
|_____|0.00852__|Deviation____________________________________________
+_____|
Report produced by the NYTProf_4.04 Perl profiler, developed by Tim_Bu
+nce and
Adam_Kaplan.
[download]

Though my program had 8 lines, a total of 5188 statements were processed!

Using if-then-else:

$ cat if-then-else.pl
#!/usr/local/bin/perl

my $letter = "c";

if ($letter eq "a")     {print "1";
}elsif ($letter eq "b") {print "2";
}elsif ($letter eq "c") {print "3";
}
[download]

Profiler output is:

 ____________________then_name_____________________
|Stmts|Exclusive|Reports           |Source File    |
|_____|Time_____|__________________|_______________|
|3____|13.0ms___|line • block |if-then-else.pl|
[download]

Much better!

Using a dispatch-table:

#!/usr/local/bin/perl

my $letter = "c";

my %h = (
        "a" => sub{print "1"},
        "b" => sub{print "2"},
        "c" => sub{print "3"},
);

$h{$letter}->();
[download]

And the profiler output:

 Source Code Files — ordered by exclusive time
 _____________________then_name_____________________
|Stmts|Exclusive|Reports           |Source File     |
|_____|Time_____|__________________|________________|
|5____|4.10ms___|line • block |dispatch-hash.pl|
[download]

The best!!

Of course, plain if-then-else and dispatch-hash are comparable. Depending on the use case, either may be chosen. However, it is clear that both of them are way better than Switch. For an in-production CGI application that I was tasked to improve performance of, replacing Switch with if-then-else gave a 150% improvement in performance. Many thanks to Tim Bunce and Adam Kaplan for writing that very useful tool - Devel::NYTProf.