in reply to Re: Overloading without infinite descent
in thread Overloading without infinite descent (fixed by time: see Perl 5.10.1)

This gives the advertised output, and certainly avoids the infinite descent, but it seems only to do what I want for the empty sub (or any other side-effect-free sub, I suppose)—if I execute ( bless sub { print "I am a side effect\n" } => 'Before' )->(), then I am a side effect is never printed.

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Re^3: Overloading without infinite descent
by Anonymous Monk on Aug 03, 2009 at 07:10 UTC
    Probably because that sub is never executed
[reply]
      Right, but my hope was that it would be—that is, that, upon de-referencing, the ‘pre-code’ would be executed first, then the code to which the reference actually points. Thus, I'd like to see: 
      ( bless sub { print "I am a side effect\n" } => 'Before' )->()

      [download]
      print 
      Stuff before
I am a side effect

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[select]
        BEGIN {

    package Before;
    my (%looper);
    use overload '&{}' => sub {
        my ($f) = @_;
        print "Stuff before \n";
        return $looper{ overload::StrVal($f) };
    };

    sub new {
        my ( $package, $sub ) = @_;
        my $self = bless sub { }, $package;
        my $fs = overload::StrVal($self);
        $looper{$fs} = $sub;
        use Scalar::Util();
        Scalar::Util::weaken( $looper{$fs} );
        return $self;
    }
}

package main;
{
    my $fx = sub { print "I am a side effect\n" };
    my $now = Before->new($fx);
    $now->();
    warn "fx => $fx ";
    warn "now => ", overload::StrVal $now ;
    bless $fx, 'Before';
    warn "fx => ", overload::StrVal $fx;
    $fx->();
}
__END__
Stuff before
I am a side effect
fx => CODE(0x18513ac)  at - line 27.
now => Before=CODE(0x18304d0) at - line 28.
fx => Before=CODE(0x18513ac) at - line 30.
Stuff before
Overloaded dereference did not return a reference at - line 31.

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