Iterating over objects

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

Greetings, O wise ones.

I am working on a Tk interface for my very first Useful Program^[1]. The main window contains several frames which contain very similar widgets. I want to be able to pack/packForget the frames dynamically, so to improve readibility I would like each frame to have a descriptive name. I.e. not the frames should be elements of an array or something similar.

On the other hand, since the widgets inside each frame are so similar, I thought it would make sense to pack the widgets in a loop, packing one frame per cycle. I basically have a list of elements I wanted to iterate over, so a foreach loop seemed ideal. My first (and so far only) idea was to do something like this:

use strict;
use Tk;

my $mw = MainWindow->new;

my $hello_string = "Hello";
my $silly_string = "Very Silly!!!";


my $frame1 = $mw->Frame();    
my $frame2 = $mw->Frame();     
my $frame3 = $mw->Frame();
my $frame4 = $mw->Frame();   

my %frame_var_hash = 
          ($frame1 => {-text => $hello_string, width => 7}, 
           $frame2 => {-text => $silly_string, width => 9}, 
           $frame3 => {-text => "XXXXX",       width => 35},
           $frame4 => {-text => $silly_string, width => 7});

 
foreach my $cur_frame (keys %frame_var_hash){
    
    $cur_frame->Label(
              $frame_var_hash{$cur_frame},
              -expand => 1,
              )->pack();
}
[...]
MainLoop;
[download]

I thought this was fairly clever (I impress myself easily) but Perl disagreed:

Can't locate object method label via package
"Tk::Frme=HASH(0x286D960)" (perhaps you forgot to load
"Tk::Frme=HASH(0x286D960)"? at test line 27.
[download]

My reading of the camel book suggests that the loop variable takes on the identity of whatever list element is assigned to it. For example,

foreach $element (@some_array){$element++}

actually increments the values in $some_array. Apparently this doesn't hold in a straightforward way for objects. I tried de-referencing $cur_frame, I tried using references to the frame objects as the keys in %frame_var_hash and then de-referencing $cur_frame, and I think I tried some other things but it was late and I forget.

Is there a way to make a loop like this work? Is there a better way to solve the problem? I am seated at you feet, listening.

-- Fuzzy Frog

^[1] The guts have been working for almost two years. I just want to give it a pretty face. The person who will be taking over my job has never heard of a command line.

Edited by Chady -- escaped barackets and made them into a nice footnote link.

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Re: Iterating over objects by japhy (Canon) on May 18, 2004 at 23:03 UTC
As BUU said, hash keys are only strings; you can't get the reference back out of them. That said, why not use an array of the objects and their argument list? `my @data = ( [ $frame1 => {-text => $hello_string, width => 7} ], [ $frame2 => {-text => $silly_string, width => 9} ], [ $frame3 => {-text => "XXXXX", width => 35} ], [ $frame4 => {-text => $silly_string, width => 7} ], ); for my $set (@data) { my ($frame, $settings) = @$set; $frame->Label( %$settings, # I'm pretty sure you want %$settings -expand => 1, # not just $settings... )->pack();` [download] _____________________________________________________ Jeff`[japhy]`Pinyan: Perl, regex, and perl hacker, who'd like a job (NYC-area) `s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;`	[reply] [d/l]
Re: Re: Iterating over objects by Fuzzy Frog (Sexton) on May 19, 2004 at 03:10 UTC
Thank you. I started thinking along these lines when I read BUU's message. Once /s?he/ mentioned it I rembered reading about stringification of hash keys. The problem is that printing a variable that contains a stringified reference yeilds exactly the same thing as printing a variable that contains an actual reference. I'm actually leaving tomorrow for a short vacation, so I won't be able to try this out for a few days. I had to bet some feedback on my problem before I left, though. Ohterwise I wouldn't stop thinking about it. _______________________________________________________________________ Two messages found in the same fortune cookie: -Friends ask for your time, not your money. -Time is money	[reply]
Re: Iterating over objects by BUU (Prior) on May 18, 2004 at 22:12 UTC
It's fairly simple, and documented some where (probably in the docs for hashes), hash keys are stringified and you can not get the actual object back from a stringified reference.	[reply]
Re: Iterating over objects by dimar (Curate) on May 18, 2004 at 22:58 UTC
Hiya Frog, A Related Module For Ya This does not answer your question, but I have a module that works like a 'generic argument grabber' using Tk for exactly the kind of scenario you mentioned. Read further if you (or anyone else) are interested. The Scenario You already have a working perl script and you simply want a fast, easy, and flexible way to supply arguments to that script in a 'novice-user-friendly' 'point-and-click' kinda way. The Background If you are familiar with VBScript or JavaScript, you probably have heard of the input box function, which simply pops up a quick-and-dirty text box for user input. This is useful, but it suffers many limitations: It only allows a 'textbox' input control It only allows a single input control It offers no flexibility for 'morphing' the input dialog My Module: Synopsis Suppose you have a script 'CreateNewEmployee.pl' that requires some input arguments, and you want an input dialog to let the novice user supply the arguments. Here is some sample code ... `### Example 000 my $get_args = {}; $get_args->{fname} = ''; $get_args->{lname} = ''; $get_args->{title} = ''; $get_args->{dept } = ''; my $usr_input = &TkDataDialog($get_args,'data_rec'); &DoCreateTheEmployeeFunction( $usr_input->{fname}, $usr_input->{lname}, $usr_input->{title}, $usr_input->{dept }, );` [download] This example pops up a dialog that lets the user supply the specified values in a predictable looking input form. You can also use compact syntax to accomplish the same thing. `### Example 001 (compact syntax) my $usr_input = &TkDataDialog( 'fname lname title dept', 'fld_list',); &DoCreateTheEmployeeFunction( $usr_input->{fname}, $usr_input->{lname}, $usr_input->{title}, $usr_input->{dept }, );` [download] My Module: Motivation I wrote this to solve exactly the kind of problem you are talking about, and because I couldn't find anything on CPAN that matched my requirements closely enough. Feature Highlights Ability to specify Input Dialog using alternate syntax styles (eg XML, 'CSS-similar', quote words, perl hashref) Ability to specify any number of input fields Ability to specify different types of input controls (default is the plain-vanilla input box, but you can also use 'select list' or 'textarea') Ability to specify Caption (aka Field label, aka 'friendly name'), Default Value, and Preset Option List for each input field Ability to specify the order in which the input fields should appear on the input form Ability to do all this stuff in a single function call without having to learn Tk Feature Lowlights No ability to control the placement of widgets within the frame No ability to add 'tooltips' or help that show the user the semantics behind each input field. (although if I knew enough Tk I'd put this in) This code is just for those cases where you want a quick and dirty way to get input of a simple data record (aka name value pairs) and you dont really care about the exact appearance of the Tk window. My Module: Dependencies `use Tk; use Tk::BrowseEntry; use Tk::DialogBox; use XML::Twig; ## to support xml-dialog syntax format use CSS::Tiny; ## to support css-like dialog syntax use Data::Dumper; ## only used for debugging and tests` [download]	[reply] [d/l] [select]
Re: Iterating over objects by Fuzzy Frog (Sexton) on May 18, 2004 at 21:55 UTC
I am (was?) the OP. I think I switched browser windows without logging back in. Grrrrrrr^. -- Fuzzy Frog ^Yes, frogs can growl.	[reply]

A Related Module For Ya

The Scenario

The Background

My Module: Synopsis

My Module: Motivation

My Module: Dependencies