When writing a complex application or network service in Perl, you might want to make a large number of commands available to your users. Such a program might have code like this to examine the user's selection and take appropriate action:
You can also store references to functions in your data structures, just as you can store references to arrays or hashes:if ($cmd =~ /^exit$/i) { exit } elsif ($cmd =~ /^help$/i) { show_help() } elsif ($cmd =~ /^watch$/i) { $watch = 1 } elsif ($cmd =~ /^mail$/i) { mail_msg($msg) } elsif ($cmd =~ /^edit$/i) { $edited++; editmsg($msg); } elsif ($cmd =~ /^delete$/i) { confirm_kill() } else { warn "Unknown command: `$cmd'; Try `help' next time\n"; }
In the second to last line, we check whether the specified command name (in lowercase) exists in our "dispatch table", %HoF. If so, we invoke the appropriate command by dereferencing the hash value as a function and pass that function an empty argument list. We could also have dereferenced it as &{ $HoF{lc $cmd} }(), or, as of the 5.6 release of Perl, simply $HoF{lc $cmd}().%HoF = ( # Compose a hash of functions exit => sub { exit }, help => \&show_help, watch => sub { $watch = 1 }, mail => sub { mail_msg($msg) }, edit => sub { $edited++; editmsg($msg); }, delete => \&confirm_kill, ); if ($HoF{lc $cmd}) { $HoF{lc $cmd}->() } # Call function else { warn "Unknown command: `$cmd'; Try `help' next time\n" }
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