Re: Improved CGI Design

Strikes me that what you have at the moment is a combination of dispatch table and if/else tree. I have tended to go with pure if/else trees because I find them easy to get my head round. But this thread stimulated me to think through dispatch tables again. My suggestion wd be to fill out the hash with default values, so that for every possible combination of keys there is a value. I'd then make the variables you set up at the beginning return keys (in fact you could cut out that step altogether by making the form send the keys - but I agree it's a good idea to have that step in case someone changes the form). If you did that then I *think* you could cut out the if/else altogether (but I should add that I haven't tested the below code - it will in any event suffice to show what I'm talking about).

sub get_branch_function {
    my $query = shift;

# get all three levels of keys into variables,
# setting defaults as necessary:
    my $action  = $query->param('action') ? $query->param('action') : 
+'default';
    my $confirm = $query->param('confirm') ? 'confirm' : 'default';
    my $commit  = $query->param('commit')  ? 'commit' : 'default';

# set up the hash so that whatever combination of keys
# it gets, it will produce a value:
    my %dispatch = (
        add => {
            confirm => {
                commit  => \&commit_dialog,
                default => \&add_dialog,
            },
            default => {
                commit  => \&add_dialog,
                default => \&add_dialog,
            },
        },
        remove => {
            confirm => {
                commit  => \&commit_dialog,
                default => \&confirm_dialog,
            },
            default => {
                commit  => \&choose_dialog,
                default => \&choose_dialog,
            },
        },
        modify => {
            confirm => {
                commit  => \&commit_dialog,
                default => \&confirm_dialog,
            },
            default => {
                commit  => \&choose_dialog,
                default => \&choose_dialog,
            },
        },
        default => {
            confirm => {
                commit  => \&action_dialog,
                default => \&action_dialog,
            },
            default => {
                commit  => \&action_dialog,
                default => \&action_dialog,
            },
        },
    );

# now one step should return the right subroutine:
    return $dispatch{ $action }{ $confirm }{ $default };

}
[download]

I agree that this makes the hash bigger; but it should not be much of a resource drain since the extra values are references; and I find the regular structure of the hash makes it easier to see what goes on.

§ George Sherston

Comment on Re: Improved CGI Design Download Code

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Re: Re: Improved CGI Design by Dogma (Pilgrim) on Apr 09, 2002 at 21:30 UTC
That is another way of implimenting the dispatch table however that really doesn't help me in thie situation. I need to have one of the hash entries be "deeper" then the rest. Your example is basicly what I already have - a table that works if all entries have the same depth. Although it does help simplify the IF/THEN/ELSE that is remaing. Cheers, -Dogma	[reply]
Re: Re: Re: Improved CGI Design by George_Sherston (Vicar) on Apr 10, 2002 at 11:33 UTC
Yes, I see. I suppose the logic of my approach is to add another level throughout the hash. Then it does get quite big, though it also remains logical and regular in a slightly obsessive-compulsive way. Untested: sub get_branch_function { my $query = shift; my $action = $query->param('action') ? $query->param('action') : +'default'; my $update = $query->param('update') ? 'update' : 'default'; my $confirm = $query->param('confirm') ? 'confirm' : 'default'; my $commit = $query->param('commit') ? 'commit' : 'default'; my %dispatch = ( add => { update => { confirm => { commit => \&commit_dialog, default => \&add_dialog, }, default => { commit => \&add_dialog, default => \&add_dialog, }, }, default => { confirm => { commit => \&commit_dialog, default => \&add_dialog, }, default => { commit => \&add_dialog, default => \&add_dialog, }, }, }, remove => { update => { confirm => { commit => \&commit_dialog, default => \&confirm_dialog, }, default => { commit => \&choose_dialog, default => \&choose_dialog, }, }, default => { confirm => { commit => \&commit_dialog, default => \&confirm_dialog, }, default => { commit => \&choose_dialog, default => \&choose_dialog, }, }, }, modify => { update => { confirm => { commit => \&commit_dialog, default => \&confirm_dialog, }, default => { commit => \&choose_dialog, default => \&choose_dialog, }, }, default => { confirm => { commit => \&choose_dialog, default => \&choose_dialog, }, default => { commit => \&choose_dialog, default => \&choose_dialog, }, }, }, default => { update => { confirm => { commit => \&action_dialog, default => \&action_dialog, }, default => { commit => \&action_dialog, default => \&action_dialog, }, }, default => { confirm => { commit => \&action_dialog, default => \&action_dialog, }, default => { commit => \&action_dialog, default => \&action_dialog, }, }, }, ); return $dispatch{ $action }{ $update }{ $confirm }{ $commit }; } [download] § George Sherston	[reply] [d/l]