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Stripping bad entries from a constructor

by jynx (Priest)
on Jan 19, 2001 at 05:59 UTC ( #52909=snippet: print w/ replies, xml ) Need Help??

Description: One of the issues that Object-Oriented programming has blessed us with is data encapsulation. For the most part it's a boon. Unfortunately, If you look at some of the standard code out there that gets used in Objects in Perl, people have the ability to assign things to objects that have no business being there.

When i wrote this originally it was to make a fine distinction between calling an Object's accessor method and calling the item explicitly. What i did was set up the object so that all the items (in a hash) had a leading underscore; no big deal. My accessor methods have no leading underscore, thus the distinction.

But rather than force people to use a leading underscore, i wanted to make the underscore optional. So i came up with the following (both versions).

Later i realized this is a good practice (IMHO) just so that people don't add things to your object hil-nil. i've been using it ever since...

jynx


ps Please tell me of any errors or bugs or improvements you can think of for the code.

pps Sorry if there's bad formatting, there's no preview button in the Snippets Section!!!


# Both have the following pragmas in place:
#!/usr/bin/perl -w
use strict;
use Carp;

#=================================================
#Version 1: no extra variable (slightly confusing)
#=================================================

   # Get the keys of @_
   foreach (keys %{ +{ @_ } }) {
      # Check to see if a key has a leading underscore
      ($self->{"_$_"} = ${ +{@_} }{$_}),next if (exists $self->{"_$_"}
+);

      # Check to see if a key has no leading underscore
      (exists $self->{$_})          ?
       $self->{$_} = ${ +{@_} }{$_} :
      # Warn the user if the key isn't valid
       carp "The entry $_ is not a valid key.\n";
   }


#================================
# Version 2: a spare %tmp to help
#================================

   # Get the keys of @_
   my %tmp = ( @_ );
   foreach (keys %tmp) {
      # Check to see if a key has a leading underscore
      ($self->{"_$_"} = $tmp{$_}),next if exists $self->{"_$_"};

      # Check to see if a key has no leading underscore
      (exists $self->{$_})         ?
         $self->{$_} = $tmp{$_}    :
      # Warn the user if the key isn't valid
         carp "The entry $_ is not a valid key.\n";
   }

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