tlm wrote:

Ultimately, my preferred code for this would be something like 

my $self = bless deep_copy( \%default_values ), $class;

[download]

where deep_copy takes a reference as argument and returns a reference to a deep copy of it.

I struggled with this some more but, as long as my default values were stored in a hash referenced by the testing subroutine, kept coming up with the same problem. Here's a little program I wrote which takes all the OO stuff out and demonstrates that, contrary to my hope/expectation, %default_values does indeed get transformed over a series of code blocks. 

#!/usr/local/bin/perl
use strict;
use warnings;
use Data::Dumper;

my $count = 0;

my %default_values = (
    SUBJECT  => 'Subject (<= 44 characters) goes here',
    AUTHOR   => {
        NAME         => 'A. U. Thor',
        CPANID       => 'AUTHOR',
        WEBSITE      => 'http://a.galaxy.far.far.away/modules',
        EMAIL        => 'a.u.thor@a.galaxy.far.far.away',
    },
);

compare( { %default_values }, 
  {
    'NAME'     => 'ABC::Alpha',
    'AUTHOR'   => { 
                    NAME   => 'James E Keenan',
                    EMAIL  => 'jkeenancpan.org',
    },
  }
);

compare( { %default_values }, 
  {
    'NAME'     => 'ABC::Alpha',
    'AUTHOR'   => { 
                    NAME   => 'James E Keenan',
                    CPANID => 'JKEENAN',
    },
  }
);

print "\nFinished\n";

sub compare {
    print "\nStart TEST ", ++$count, "----------\n\n";
    my ($dvref, $paramsref) = @_;
    print Dumper ($dvref, $paramsref);
    my %dv = %{ $dvref };
    my %parameters = %$paramsref; 
    foreach my $param ( keys %parameters ) {
        if ( ref( $parameters{$param} ) eq 'HASH' ) {
            foreach ( keys( %{ $parameters{$param} } ) ) {
                $dv{$param}{$_} = $parameters{$param}{$_};
            }
        }
        else {
            $dv{$param} = $parameters{$param};
        }
    }
    print Dumper (\%dv);
}

[download]

Note that what is dumped for $dvref the second time around differs from what the first time.

I have, however, found a solution: Localize %default_values within a subroutine and have that sub return a reference to that hash. The above program gets transformed into: 

compare( default_values(), 
  {
    'NAME'     => 'ABC::Alpha',
    'AUTHOR'   => { 
                    NAME   => 'James E Keenan',
                    EMAIL  => 'jkeenancpan.org',
    },
  }
);

compare( default_values(), 
  {
    'NAME'     => 'ABC::Alpha',
    'AUTHOR'   => { 
                    NAME   => 'James E Keenan',
                    CPANID => 'JKEENAN',
    },
  }
);

sub default_values {
    my %default_values = (
            SUBJECT  => 'Subject (<= 44 characters) goes here',
            AUTHOR   => {
                NAME         => 'A. U. Thor',
                CPANID       => 'AUTHOR',
                WEBSITE      => 'http://a.galaxy.far.far.away/modules'
+,
                EMAIL        => 'a.u.thor@a.galaxy.far.far.away',
            },
    );
    return { %default_values };
}
}

[download]

The constructor is transformed in this manner: 

    my $self = ref($class) ? bless( default_values(), ref($class) )
                           : bless( default_values(), $class );

[download]

So, instead of the constructor blessing a reference to a hash of default values, it blesses the return value of a subroutine where that value is in turn a reference to the hash of default values.

As I said at the outset, this example was a stripped-down version of a problem I was facing with the ongoing development of a module I maintain. Ironically, the solution above is the solution which the original module author (Geoff Avery) came up with in earlier versions of the module (ExtUtils::ModuleMaker). Plus ça change ....

Thanks again.

In reply to Re^4: Wrong Error Message When Testing for Failure of Constructor by jkeenan1
in thread Wrong Error Message When Testing for Failure of Constructor by jkeenan1

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.