Reducing the complexity of dispatch tables

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

With the help and patience of wfsp, Anno and others on the CB, I was able to trim out some fat in my existing dispatch tables for a site I'm rewriting.

What I'm currently left with (which works, so far), is this:

 my %dispatch = (
        home            => \&home,
        donate          => \&donate,
        news            => \&news,
        samp            => sub { \&samples($dbh) },
        ...
);

$action         = $apr->param('a') || 'home';
$dispatch{$action}->($action);

sub render_template {
        my ($action, $params) = @_; 
 
        my $template    = HTML::Template->new(
                                die_on_bad_params => '0',
                                filename => "$action");
        my $content     = $template->output;
        print $content;
}

sub home {
        my ($action, $params) = @_;
        return render_template($action, $params);
}

sub donate {
        my ($action, $params) = @_;
        return render_template($action, $params);
}

sub news {
        my ($action, $params) = @_;
        return render_template($action, $params);
}

sub samples {

        my ($dbh) = shift;
        ....
}
[download]

Note: There's one small bug I just found when composing this (if I pass an unknown param, it should default to 'home', but it doesn't, it just dies with Can't use string ("") as a subroutine ref while "strict refs" in use). I'll try to fix that shortly.

What I'm wondering now, is with these subs being identical now except for their sub name... can I make these into anonymous subs, and pass the $action down to them, reducing the 20+ identical subs down to 1?

Comment on Reducing the complexity of dispatch tables Select or Download Code

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Re: Reducing the complexity of dispatch tables by ikegami (Patriarch) on Aug 31, 2007 at 15:15 UTC
You could just refer to the same sub more than once: `my %dispatch = ( home => \&default, donate => \&default, news => \&default, samp => sub { \&samples($dbh) }, ... ); $action = $apr->param('a'); $action = 'home' if !exists $dispatch{$action}; $dispatch{$action}->($action); sub default { my ($action, $params) = @_; return render_template($action, $params); } sub samples { my ($action, $dbh) = shift; ... }` [download] Shortcut: `my %dispatch = ( (map { $_ => \&default } qw( home donate news )), samp => sub { \&samples($dbh) }, ... );` [download]	[reply] [d/l] [select]
Re: Reducing the complexity of dispatch tables by jdporter (Paladin) on Aug 31, 2007 at 16:43 UTC
I'd consider using a namespace (package) rather than a dispatch table (hash). The concept is the same, but you get name checking for free and it's probably faster. use strict; use warnings; { package Dispatch; sub render_template { my ($action, $params) = @_; print "render_template( action => $action, params => $params ) +\n"; } home = donate = news = sub { my $pkg = shift; my ($action, $params) = @_; return render_template($action, $params); }; sub samples { my ($dbh) = shift; print "samples( dbh = $dbh )\n"; } sub samp { my $pkg = shift; samples('$DBH'); } sub AUTOLOAD { my $pkg = shift; our $AUTOLOAD; print "Error: no such function $AUTOLOAD ( @_ )\n"; } } # test: for my $act ( qw( home donate news samp bogus )) { Dispatch->$act($act,"PARAMS"); } [download] Note - You'll get a "used only once" warning on the assignments to `home` etc. To squelch it, you can enclose those assignments in a block like so: `{ no warnings 'once'; . . . }` [download] A word spoken in Mind will reach its own level, in the objective world, by its own weight	[reply] [d/l] [select]
Re: Reducing the complexity of dispatch tables by BrowserUk (Patriarch) on Aug 31, 2007 at 17:15 UTC
Your entire dispatch table can be replaced by the following 2 lines: `$action = $apr->param('a') \|\| 'home'; render_template( $action, $action );` [download] Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l]
Re^2: Reducing the complexity of dispatch tables by moritz (Cardinal) on Aug 31, 2007 at 17:48 UTC
Not quite: in this version an invalid but defined `$action` will reach `render_template`.	[reply] [d/l] [select]
Re^3: Reducing the complexity of dispatch tables by BrowserUk (Patriarch) on Aug 31, 2007 at 18:15 UTC
True, but with the addition of a check for failure of HTML::Template to find an appropriate file... Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply]
Re^2: Reducing the complexity of dispatch tables by jdporter (Paladin) on Aug 31, 2007 at 19:12 UTC
Um... What about the `samp` entry, which runs the `sample` subroutine?	[reply] [d/l] [select]
Re^3: Reducing the complexity of dispatch tables by BrowserUk (Patriarch) on Aug 31, 2007 at 19:22 UTC
Oh gosh. You got me? .oO(rename the template...or `$action =~ s[samp][sample]`...or use a hash to tranform short names to long ones...or) Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l]


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