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

Examine the following code: 
package Foo_parent;

sub new { print "@_\n"; }

package Foo_child;

@{'Foo_child::ISA'} = 'Foo_parent';

package Bar;

my @args = 1 .. 3;

*{'Foo_child::new'} = sub {
    my $self = shift;
    $self->SUPER::new( @args );
};

package main;

my $foo = Foo_child->new;

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Now, without running it, what do you think it should do? My thoughts were: 

Foo_child 1 2 3

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In fact, what happens is: 

Can't locate object method "new" via package "Bar" at ./foo.pl line 17
+.

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My question is why doesn't this DWIM? And, how can I make it DWIM? I'm using 5.8.x, if that matters ...

Being right, does not endow the right to be rude; politeness costs nothing.
Being unknowing, is not the same as being stupid.
Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence.
Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.

Replies are listed 'Best First'.
•Re: Auto-generated constructors not finding correct SUPER?
by merlyn (Sage) on Jan 09, 2005 at 19:36 UTC
    SUPER is relative to __PACKAGE__, and the __PACKAGE__ of your constructor is Bar, not Foo_child. Be sure you have "package Foo_child" before you use SUPER there.

    So, for example, your code doesn't work: 

    package Wrong; *{'Right::new'} = sub { ... SUPER ... };

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    nor does this: 
    package Wrong; sub Right::new { ... SUPER ... }

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    but this does: 
    package Right; sub new { ... SUPER ... }

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    as does this: 
    package Wrong; sub Right::new { package Right; ... SUPER ... }

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    -- Randal L. Schwartz, Perl hacker
    Be sure to read my standard disclaimer if this is a reply.

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      So, given that, how would I make the following code work in package Right? My problem is that I need to create constructors that are closures ... 
      package Wrong;

sub builder {
    my $pkg = shift;

    my @args = (
        # A bunch of random stuff here, including objects
    );

    {
        no strict 'refs';
        *{ $pkg . '::new' } = sub {
            (shift)->SUPER::new( @args );
        };
    }
}

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      Being right, does not endow the right to be rude; politeness costs nothing.
      Being unknowing, is not the same as being stupid.
      Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence.
      Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.

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[d/l]
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Re: Auto-generated constructors not finding correct SUPER?
by simonm (Vicar) on Jan 10, 2005 at 19:24 UTC
    I ran into a vaugely-related problem with SUPER last year. (1, 2, 3)

    If you want to avoid string evals, another approach might be to replace the use of SUPER with NEXT or Class::MixinFactory::NEXT. These perform a similar function, re-dispatching to superclass methods, but use other techniques to search the inheritance tree. As a result, they are slower than SUPER, but might work better in your situation.

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