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Re: Command line tool coding style?

by perrin (Chancellor)
on Jan 16, 2002 at 02:46 UTC ( #139070=note: print w/ replies, xml ) Need Help??


in reply to Command line tool coding style?

Why use OO for this?

if (defined &$action) { &$action; } else { die "Unknown action '$action'\n\nUsage here\n"; }


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Re^2: Command line tool coding style?
by Aristotle (Chancellor) on Jan 16, 2002 at 05:34 UTC
    Two reaons: strict and the GetOptions() hash. The latter was actually what gave me the idea in the first place. The script started out having a series of
    { do_this(\%options, $table), last if $action eq 'this'; do_that(\%options, $table), last if $action eq 'that'; # ... die "Usage here\n"; }
    Look a bit harder and you'll see method calls in disguise.. With this new approach, all I have to do is write sub _more {} and the script will automatically understand the "more" option - and it works with strict too. (Plus can $execute $_action looks much prettier than defined &$_action IMHO :-))
      You can easilly get by strict if you use this:
      eval('&' . $action . '()'); if( $@ ) { die "Usage\n"; }
      It might be good to check the text of the exception here to make sure it's from a missing sub. You might even be able to do this:
      my $subref = \&{$action}; die "Usage" unless defined &$subref();
      I haven't tried that last though.

      There's just no good reason to use OO here, and it makes the code more confusing and JAPH-ish. Maybe there's something else in your program that justifies OO, but this problem doesn't.

      Incidentally, a nicer way to write that dispatch table from your above comment would be something like this (untested):

      my %dispatch = ( 'this' => \&do_this, 'that' => \&do_that, ); if (defined $dispatch{$action}) { &$dispatch{$action}; } else { die "Usage\n"; }

        I actually agree it is sort of JAPHish - that's why I posted it as a question here. I went through thinking about a dispatch table exactly the way you proposed, as I already explained in my reply to chromatic, but it has the same problem as the switch-construct: adding an "action handler" requires maintaining the dispatch table. I could have put the handlers as anonymous subs right into the dispatch table, but then I have to define them before the body of the main program and they're very long. (The biggest one is 2.5 pages of straight-through code without any loops.)

        I sort of like your eval proposition, though the idea of circumventing strict in whichever fashion irks me. :-)

        Thinking about it some more I think the sole reason it turns JAPHish is the role I have given to new() - that's the single thing I would point out as contrived in retrospect. I wonder if it's possible (and what you'd think) of doing something along the following lines:

        #!/usr/bin/perl use warnings; use strict; print "\nfoo script\n\n"; my $action = shift(@ARGV); die "Usage here\n" unless $action; my $handler = can main "_$action"; die "Unknown action '$action'\n\nUsage here\n" unless ref $handler; my %params; GetOptions(\%params, qw(various options here)); # do more stuff with %params here $handler->(\%params); exit; ###################################################################### +## ###################################################################### +## use Getopt::Long; # use Other::Modules::Here; # .. etc ..

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